Author Topic: Fixed HP1741A in a big shape but... I bet in a focus problem, and you? (Read 65694 times)

Alex Eisenhut · « **Reply #1 on:** February 05, 2016, 01:43:05 am »

You are in storage mode, you might have some trapped charge. Turn down the beam intensity to 0 and press erase a few times. If that doesn't work, there is a deep erase button on the back, follow the procedure in the manual.

SAUL BRITTO · « **Reply #2 on:** February 05, 2016, 01:56:54 am »

Thank you Alex Eisenhut. Actually this scope is still coming to me, this is a picture that the seller sent me.
I hope you are right.

edpalmer42 · « **Reply #3 on:** February 05, 2016, 02:59:33 am »

I have the 1744A - an enhanced version of the 1741A. I didn't look it up, but I think the writing speed on mine is much faster. I normally run with the Brightness control fully CCW, the intensity much lower than shown in the picture, and the focus at about 12:00. With the Brightness control turned up, blooming like in the picture is guaranteed to happen. You have to balance the Persistence, Brightness, and Intensity. They all have to change as you change the Horizontal speed. But when you get them right, it's glorious!

SAUL BRITTO · « **Reply #4 on:** February 05, 2016, 03:08:15 am »

Quote from: edpalmer42 on February 05, 2016, 02:59:33 am

I have the 1744A - an enhanced version of the 1741A. I didn't look it up, but I think the writing speed on mine is much faster. I normally run with the Brightness control fully CCW, the intensity much lower than shown in the picture, and the focus at about 12:00. With the Brightness control turned up, blooming like in the picture is guaranteed to happen. You have to balance the Persistence, Brightness, and Intensity. They all have to change as you change the Horizontal speed. But when you get them right, it's glorious!

What really does that deep erase? Of course I suppose, but I would like a clarification if possible.

SAUL BRITTO · « **Reply #5 on:** February 05, 2016, 03:36:03 am »

Deep erase on the manual looks like a dangerous process!!!

coppice · « **Reply #6 on:** February 05, 2016, 03:51:50 am »

Quote from: edpalmer42 on February 05, 2016, 02:59:33 am

I have the 1744A - an enhanced version of the 1741A.

In what way was the 1744A enhanced? I remember it as cost reduced model with a limited display area.

edpalmer42 · « **Reply #7 on:** February 05, 2016, 04:05:24 am »

Quote from: SAUL BRITTO on February 05, 2016, 03:36:03 am

Deep erase on the manual looks like a dangerous process!!!

I don't know. The 1744A doesn't have 'Deep Erase'. The manual only talks about B-scan for erasing deeply stored images, but I've never used it.

Ed

edpalmer42 · « **Reply #8 on:** February 05, 2016, 04:11:44 am »

Quote from: coppice on February 05, 2016, 03:51:50 am

Quote from: edpalmer42 on February 05, 2016, 02:59:33 am
I have the 1744A - an enhanced version of the 1741A.
In what way was the 1744A enhanced? I remember it as cost reduced model with a limited display area.

Oh, so now you're going to force me to look it up! Fine! Be like that!

Just kidding!

They're both 100 MHz, but the 1741A has a storage writing speed of > 100 cm/us. The 1744A has a storage writing speed of > 1800 cm/us.

SAUL BRITTO · « **Reply #9 on:** February 05, 2016, 04:21:52 am »

Look at this:

SAUL BRITTO · « **Reply #10 on:** February 05, 2016, 04:23:59 am »

But,guys: can't be a focus defect, anyway?

edpalmer42 · « **Reply #11 on:** February 05, 2016, 04:42:05 am »

Quote from: SAUL BRITTO on February 05, 2016, 04:23:59 am

But,guys: this can't be a focus deffect, anyway?

Yes, it could be defective. Until you get it on your bench you won't know for sure.

SAUL BRITTO · « **Reply #12 on:** February 05, 2016, 04:49:08 am »

Quote from: edpalmer42 on February 05, 2016, 04:42:05 am

Quote from: SAUL BRITTO on February 05, 2016, 04:23:59 am
But,guys: this can't be a focus deffect, anyway?

Yes, it could be defective. Until you get it on your bench you won't know for sure.

I think will measure this voltage very well, I do have a high V RCA probe that measures 58kv,maybe this focus V is around 2kv?

edpalmer42 · « **Reply #13 on:** February 05, 2016, 05:19:59 am »

Quote from: SAUL BRITTO on February 05, 2016, 04:49:08 am

Quote from: edpalmer42 on February 05, 2016, 04:42:05 am
Quote from: SAUL BRITTO on February 05, 2016, 04:23:59 am
But,guys: this can't be a focus deffect, anyway?

Yes, it could be defective. Until you get it on your bench you won't know for sure.
I think will measure this voltage very well, I do have a high V RCA probe that measures 58kv,maybe this focus V is around 2kv?

Okay Saul, I'm onto you now! You're just looking for an excuse to take it apart and poke at it. Haven't you learned yet? We don't need an excuse! We do it 'cause we want to!

Just follow the procedure in the manual to measure the HV. It tells you where, how, and what you should measure.

SAUL BRITTO · « **Reply #14 on:** February 05, 2016, 05:26:00 am »

Quote from: edpalmer42 on February 05, 2016, 05:19:59 am

Quote from: SAUL BRITTO on February 05, 2016, 04:49:08 am
Quote from: edpalmer42 on February 05, 2016, 04:42:05 am
Quote from: SAUL BRITTO on February 05, 2016, 04:23:59 am
But,guys: this can't be a focus deffect, anyway?

Yes, it could be defective. Until you get it on your bench you won't know for sure.
I think will measure this voltage very well, I do have a high V RCA probe that measures 58kv,maybe this focus V is around 2kv?

Okay Saul, I'm onto you now! You're just looking for an excuse to take it apart and poke at it. Haven't you learned yet? We don't need an excuse! We do it 'cause we want to!

Just follow the procedure in the manual to measure the HV. It tells you where, how, and what you should measure.

No I do not have it in my hands right now. I'm just trying to get an idea of what I purchased blindly. I have two HP1740A and already have a little experience with these scopes not so much with the hp1741a, for its storage resource

oldway · « **Reply #15 on:** February 05, 2016, 12:59:32 pm »

In my opinion, this scope has no fault, only wrong settings.
The guy who sell this scope does not know how to operate this scope.
See on brighter picture:
What's wrong ?
Delay time base selected instead of main time base.
Main time base not triggered because no input signal and automatic trigger is not selected.
Focus almost anticlockwise.

SAUL BRITTO · « **Reply #16 on:** February 05, 2016, 04:59:22 pm »

oldway> I do not know if the seller is a technician or has any knowledge in this area

oldway · « **Reply #17 on:** February 05, 2016, 07:00:56 pm »

Quote from: SAUL BRITTO on February 05, 2016, 04:59:22 pm

oldway> I do not know if the seller is a technician or have any knowledge in this area

Looking at the picture, he has not for sure

SAUL BRITTO · « **Reply #18 on:** February 05, 2016, 07:52:08 pm »

Quote from: oldway on February 05, 2016, 07:00:56 pm

Quote from: SAUL BRITTO on February 05, 2016, 04:59:22 pm
oldway> I do not know if the seller is a technician or have any knowledge in this area
Looking at the picture, he has not for sure

Good laughs here!

Alex Eisenhut · « **Reply #19 on:** February 06, 2016, 02:52:03 am »

I agree with oldway, I remember seeing that kind of bloom when the settings are wrong. I think leaving a bloom like that in the CRT while it's OFF is not a good idea.
But if it survives shipping, it means at least everything is working.
Deep erase can be dangerous, it's only a last resort.
I no longer have the 1741, I gave it away years ago. But I remember it had a burned-in image from the lab it came from, it took a lot of erasing and fiddling to get the image to disappear.

If you press erase a few times and it doesn't go away, run it in auto erase with no input signal, put it in auto mode with no beam intensity and it will store nothing and erase the screen continuously.

This is also in the manual IIRC.

SAUL BRITTO · « **Reply #20 on:** February 06, 2016, 05:13:16 am »

Quote from: Alex Eisenhut on February 06, 2016, 02:52:03 am

I agree with oldway, I remember seeing that kind of bloom when the settings are wrong. I think leaving a bloom like that in the CRT while it's OFF is not a good idea.
But if it survives shipping, it means at least everything is working.
Deep erase can be dangerous, it's only a last resort.
I no longer have the 1741, I gave it away years ago. But I remember it had a burned-in image from the lab it came from, it took a lot of erasing and fiddling to get the image to disappear.

If you press erase a few times and it doesn't go away, run it in auto erase with no input signal, put it in auto mode with no beam intensity and it will store nothing and erase the screen continuously.

This is also in the manual IIRC.

Thank you Alex.I believe now will look this scope with a bit more care

SAUL BRITTO · « **Reply #21 on:** February 06, 2016, 05:16:53 am »

Guys please, be pacient with my "english" because I speak portuguese and to me it's beeing hard.

SAUL BRITTO · « **Reply #22 on:** February 06, 2016, 05:20:58 am »

I already have some experience with this HP scopes because, I have a few more 1740A that was defective and repaired myself and I think they are excellent.

SAUL BRITTO · « **Reply #23 on:** February 06, 2016, 05:23:10 am »

It cost me about $ 40 with shipping fee. It was a good price?

SAUL BRITTO · « **Reply #24 on:** February 11, 2016, 11:52:54 pm »

Hi friends. When I worked with tube tv, seen many triplers causing a similar defect. As the anode lost the ability to attract the electron beam causing, this type of screen. Tomorrow the courier will deliver the scope in my home.

Alex Eisenhut · « **Reply #25 on:** February 12, 2016, 12:58:30 am »

Quote from: SAUL BRITTO on February 11, 2016, 11:52:54 pm

Hi friends. When I worked with tube tv, seen many triplers causing a similar defect. As the anode lost the ability to attract the electron beam causing, this type of screen. Tomorrow the courier will deliver the scope in my home.

Good luck! But before tearing everything apart, remember it's tricky to get working in storage mode; don't assume it's broken right away!

SAUL BRITTO · « **Reply #26 on:** February 12, 2016, 02:40:54 am »

Quote from: Alex Eisenhut on February 12, 2016, 12:58:30 am

Quote from: SAUL BRITTO on February 11, 2016, 11:52:54 pm
Hi friends. When I worked with tube tv, seen many triplers causing a similar defect. As the anode lost the ability to attract the electron beam causing, this type of screen. Tomorrow the courier will deliver the scope in my home.

Good luck! But before tearing everything apart, remember it's tricky to get working in storage mode; don't assume it's broken right away!

Hi Alex,how are you guy? Thank you for advise.

I'm not interested storage. I just want it running smoothly

SAUL BRITTO · « **Reply #27 on:** February 12, 2016, 02:43:28 am »

I do have a tektronix 2220 that have storage mode but ,I never used,my use of oscilloscope is very simple

SAUL BRITTO · « **Reply #28 on:** February 12, 2016, 10:20:32 pm »

Hi All. The scope finally is in my bench. I did a small video,look:
https://youtu.be/SpsUYWx4-_0

rf+tech · « **Reply #29 on:** February 13, 2016, 03:44:55 am »

Hello Saul,

First thing to try is turn OFF storage mode.

Turn the scope around, on the back panel is a pushbutton marked "Conv". This to the right of the black CRT cover.
Press this button to place the scope in Conventional mode.
The "Conv" light on the front panel should now be ON and the scope should display a trace that can be properly focused.

Here's the HP1741 manual: http://cp.literature.agilent.com/litweb/pdf/01741-90911.pdf.

Section 3 covers the operation of this analog storage scope, and Section 5-59 describes the storage adjustments procedures.

Without the knowledge necessary to use analog storage mode - and most importantly - how to properly adjust these "unconventional" scope controls, it is possible to end up looking for something that does not need to be repaired. The blooming present in the video appears "normal" to me for an old scope that has not had the storage adjustment procedure performed in many years.

I once owned an HP1727 275 MHz storage scope, getting the collimator and flood guns properly adjusted on these old HP analog storage scopes can be a challenge. Once adjusted, the illumination may still not be uniform across the screen. It all becomes a compromise.

RF+ Tech

SAUL BRITTO · « **Reply #30 on:** February 13, 2016, 04:20:59 am »

Wow! Thank you so mutch rf+tech.It was of a big help to me! I will do this and report what happened.

SAUL BRITTO · « **Reply #31 on:** February 13, 2016, 04:30:34 am »

rf+tech when I use conventional mode I get a black screen. No trace,no bright, nothing but,I found a transistor
Q17 on the vertical board that seems in short thre is a diode near to it that looks in short. There is a -12 Volts with -14,2V. You see a connection between these things?

SAUL BRITTO · « **Reply #32 on:** February 13, 2016, 04:57:39 am »

SAUL BRITTO · « **Reply #33 on:** February 13, 2016, 05:02:34 am »

At this place has a 2n4035

rf+tech · « **Reply #34 on:** February 13, 2016, 01:21:32 pm »

Saul,

Where is this diode that may be shorted? I see no diodes in the attached schematic.

Please provide the voltages measured on each lead of Q17. One measurement by itself is meaningless.
Since Q17 and Q18 comprise a differential amplifier, it is better to evaluate both sides together.
Let's see all six measurements.

And have all power supply voltages been checked, before jumping into the vertical amplifier?

RF+ Tech

SAUL BRITTO · « **Reply #35 on:** February 13, 2016, 03:54:48 pm »

Quote from: rf+tech on February 13, 2016, 01:21:32 pm

Saul,

Where is this diode that may be shorted? I see no diodes in the attached schematic.

Please provide the voltages measured on each lead of Q17. One measurement by itself is meaningless.
Since Q17 and Q18 comprise a differential amplifier, it is better to evaluate both sides together.
Let's see all six measurements.

And have all power supply voltages been checked, before jumping into the vertical amplifier?

RF+ Tech

Q17 is: base -12.17V, collector and emmiter -14.12V. Q18 is working very very hot! I will to see all the PS, despite I did a preview yesterday night and, just found the 120V rail with 124V and, on the vertical board a -12V with -14,2V,That diode is fisicly near to this transistor but on schematic no, it isn't in this image.

rf+tech · « **Reply #36 on:** February 13, 2016, 04:54:38 pm »

Saul,

Something to make note of: the A17 schematic shows +/- 12 Volts coming from A3. The A3 schematic does not show where +/- 12 Volts comes from.

Looking at the interconnecting diagrams, sheet 1 of 3 shows +/- 12 Volts at A3 block but *nowhere* can I find the source for +/- 12 Volts.

Since you measure 14.2 Volts where the schematic indicates 12 Volts, and there is no 12 Volt supply to be found, the conclusion is an error in the manual. HP was very good about releasing errata/change notices in paper form. Without access to these for the 1741, we have to conclude from the evidence of your observations that 12 Volts is really 15 Volts. 14.2 Volts is only 5.3% low from 15 Volts and does not present a problem.

Please report what the -12 Volt point measures to see if this theory is further supported.

This illustrates the importance of conveying as much information as possible. With minimal information, we can only waste time guessing at things. Even if you think the power supply voltages are good, post them for our benefit. Everyone sees things a little differently.

As for Q18 running hot, consider that the A17 is DC coupled from the A3 - specifically from A3A1. And the output balance of A3A1 depends on many more inputs. It is possible that Q18 is hot because the real problem is in the A3.

By providing the DC voltage measurements on both Q17 and Q18 emitter, base and collector, we can better evaluate and advise on the problem.

The 120 Volt supply measuring 124 Volts is of little concern as this is only 3.2% high.

RF+ Tech

SAUL BRITTO · « **Reply #37 on:** February 13, 2016, 05:07:21 pm »

That diode is connected to a -15V rail,but I can not find in the schematic,for now.

SAUL BRITTO · « **Reply #38 on:** February 13, 2016, 05:21:43 pm »

RF+ Tech >> I do have two more boards like this one (Two scopes) and those boards has different measures with the DMM in diode scale, the junction colletor emmiter of Q17 is 0.600v on the other boards and on the sick scope is full short 0.0V on diode scale. That one diode measures 0.2V and on the other board is 0.500V on diode scale.
Q17 and Q18 has each one a equal diode near it,they are connected to a -15V rail,but on the A3 vertical board I just found a transistor in this rail,at the eschematic. If you prefer I can make an image of exactly place on the board.

SAUL BRITTO · « **Reply #39 on:** February 13, 2016, 05:30:42 pm »

Here is the image.Sorry for this webcam.

SAUL BRITTO · « **Reply #40 on:** February 13, 2016, 05:41:59 pm »

The pins 5 and 6 of this connector are -12 and +12V rails.Near to Q17 has a test point connected to -12V that's measuring -14,2V.

SAUL BRITTO · « **Reply #41 on:** February 13, 2016, 06:20:25 pm »

If you see on the schematic Q17 is polarized with 12.6V on emmiter and 0.6 on collector but,here is measuring -14,2V base and emmiter and Q18 on the schema is PNP on the board is NPN wow!!

rf+tech · « **Reply #42 on:** February 13, 2016, 06:47:44 pm »

Very good information Saul.

The diodes are not likely to be VR2 and VR3, on the right side of the A17 schematic, based on their connection to -15 Volts. Do the other two boards look identical to this defective board, in this area? The fact that HP revised this differential amplifier and added these diodes, together with +/-14.2 Volts on the "+/-12" Volt rails adds confirmation that these are indeed +/- 15 Volt rails.

The diode test on Q17 certainly is conclusive. The diode test on this unknown diode may be influenced by the shorted Q17. Can you see if this diode connects in some way to Q17, perhaps through a low value resistor? It would be good to unsolder one leg of the suspect diode and try the diode test again.

I don't see the mystery Q13 (on the A3 parts layout page) on the A3 schematic, either. So far, this manual has not been very helpful. More searching has not turned up different scans of the manual.

Just now saw your new post - it would appear that someone has "repaired" this board. I "think" some people do this just to help us sharpen out troubleshooting skills.

For a quick fix, a 2N3906 should work. The bandwidth of the amplifier may suffer, but at least we will know more.

RF+ Tech

SAUL BRITTO · « **Reply #43 on:** February 13, 2016, 06:53:10 pm »

I removed the Q17 it's in full short and the short on the diode was your fault,diode is good.

SAUL BRITTO · « **Reply #44 on:** February 13, 2016, 06:59:11 pm »

That -12V seems to have origin in any way in Q17 because when I removed Q17 did a measure on that -12V and it is 0.2V now. On the others boards are absolutly equal all you find in one find on the other and,Q18 is a NPN transistor on all that.

SAUL BRITTO · « **Reply #45 on:** February 13, 2016, 07:14:24 pm »

I have an original one Q17 but, I think: what cold be te cause of this short in Q17? What do you think about?

SAUL BRITTO · « **Reply #46 on:** February 13, 2016, 08:08:28 pm »

Replaced the Q17 and some things changed your behavior,that big IC on the vertical board seems working normally,
Beause it was working cold and now is in a temperature as the other scopes. Just don't have a trace,maybe I have a tube polarization problem or in lacking of HV.

SAUL BRITTO · « **Reply #47 on:** February 13, 2016, 08:42:17 pm »

I found a tantalum cap in short on the vertical board,I will replace and see what happens

rf+tech · « **Reply #48 on:** February 13, 2016, 09:59:50 pm »

That is too strange to find NPN transistors in place of PNP, especially in a differential amplifier where both sides mirror each other. Have you compared the E-B and B-C diode drops to a known PNP or NPN to confirm this?

On another forum, I found a marked up A5 schematic for the HP1740 vertical amplifier. It is very similar to the A17 and someone has recorded many voltage measurements that may be of help:

HP 1740A Vertical Mod -0001: http://www.electro-tech-online.com/attachments/hp-1740a-vertical-mod-0001-pdf.44405/

Measuring the voltage on the vertical deflection plates will show if the amplifier can be balanced when turning the vertical position control, or if there is still another problem to locate. Knowing that the trace is not off the top or bottom is more important than jumping to the high voltage power supply.

You are making good progress.

RF+ Tech

SAUL BRITTO · « **Reply #49 on:** February 13, 2016, 10:06:28 pm »

rf+tech>> I am almost sure that the tripler is bad,Has a 58kv probe here and the way is to measure this.

I did measure the HV on the output of tripler and got about 2.8kV I think it'snt right...

SAUL BRITTO · « **Reply #50 on:** February 13, 2016, 10:11:04 pm »

Sure. I have a 1740A unit,do you know if the tripler of "40A" is the same as 41A?

SAUL BRITTO · « **Reply #51 on:** February 13, 2016, 10:26:37 pm »

On the schematic I see anything that looks like 5kV and, can't see very well because the copy is not so good.

SAUL BRITTO · « **Reply #52 on:** February 13, 2016, 10:41:52 pm »

Ok confirmed the HV is +5kV but just js generates 2.6 or 2.8 kV post tripler.

SAUL BRITTO · « **Reply #53 on:** February 13, 2016, 11:00:46 pm »

You are surely right about the transistors but, it's incredible,look http://alltransistors.com/transistor.php?transistor=2128 this is the transistor 2n2536 (Q18) how do you see it is a PNP Tr but when a measure it just seems a NPN Tr black probe on the base dont works, when I invert the probes RED on the base it works as a NPN Tr wow!
And this in two Boards There is a one I know: It works well.

SAUL BRITTO · « **Reply #54 on:** February 13, 2016, 11:48:13 pm »

Quote from: SAUL BRITTO on February 13, 2016, 10:06:28 pm

rf+tech>> I am almost shure that the tripler is bad,Has a 58kv probe here and the way is to measure this.

I did measure the HV on the output of tripler and got about 2.8kV I think it'snt right...

Ok.I measured the DC level in the plates and saw 70V and 36V on the channel that has 70V changing the potentiometer varies between 70 and 69V and 36V which has nothing happens

rf+tech · « **Reply #55 on:** February 14, 2016, 12:00:44 am »

Saul,

The HV adjustment procedure is in paragraph 5-15. This says the HV at A15TP4 is to be -2250 Volts, +/- 50 Volts.

The specifications given on page 1-5 indicate the CRT post accelerator voltage is approximately 7.5 kV.

Somehow I have missed the change notice section in the manual. There is a backdating schematic for the A15 HVPS on page 7-3 that shows approximately 5 kV from the tripler. I agree that 2.8 kVolts is not good.

If the horizontal and vertical plate voltages show the beam can be centered on-screen, I think there would be some sign of a dim trace.

A17 has many changes shown on page 7-2. There are new A17 schematics and parts placement drawings included in figures 7-6, 7-7 and 7-8. The photo you made with Q17 and Q18 circled does not match up with either parts placement. Note that the parts placement shows Q17 and Q18 are further in from the edge of the board and next to A1 which is square.

The transistors in your photo are from a different place, they are next to a 14 pin IC that is rectangular, and much closer to the edge of the board. The transistors you have marked as Q17 and Q18 are not correct. That would explain finding NPN where PNP is expected and explain the presence of the diodes, that are not shown in the schematic.

All of these differences are much too confusing. Every time I look closer at this manual, more differences are seen and this makes it more difficult to be of help.

2N2536 is a germanium transistor. The new question of the minute is why HP would use germanium at this late time in semiconductor history?

RF+ Tech

rf+tech · « **Reply #56 on:** February 14, 2016, 12:05:28 am »

Since we just cross-posted,

Quote

Ok.I measured the DC level in the plates and saw 70V and 36V on the channel that has 70V changing the potentiometer varies between 70 and 69V and 36V which has nothing happens

So the differential amplifier cannot be balanced. We would expect both plates to become equal voltage near the center of the potentiometer travel. And this tells us that the beam is deflected heavily off-screen.

RF+ Tech

SAUL BRITTO · « **Reply #57 on:** February 14, 2016, 12:09:49 am »

I just see any sgnal of trace on the non-conventional mode,on the conventional just a black screen.
To tell the truth is not a trace only a shadow of something moving on the screen.

SAUL BRITTO · « **Reply #58 on:** February 14, 2016, 12:15:04 am »

Quote from: SAUL BRITTO on February 14, 2016, 12:09:49 am

I just see any sgnal of trace on the non-conventional mode,on the conventional just a black screen.
To tell the truth is not a trace only a shadow of something moving on the screen.

Really a just see a shadow of a trace out of screen.

SAUL BRITTO · « **Reply #59 on:** February 14, 2016, 12:17:58 am »

But how can a PNP Tr acts like a NPN? sex change?

SAUL BRITTO · « **Reply #60 on:** February 14, 2016, 12:33:22 am »

I will remove it from the board to see what it is really

rf+tech · « **Reply #61 on:** February 14, 2016, 12:48:56 am »

Of course, the transistor will be an NPN transistor.

From everything I have seen in the parts placement drawings, compared to your photo, you are looking at the wrong transistors.

Whatever they are, they are not Q17 and Q18. They are some other transistors. Study the drawings and look carefully at the surrounding components. Can you now see what I see?

If you do not agree, then I must be looking at the wrong board. Is it not A17 we are discussing?

RF+ Tech

SAUL BRITTO · « **Reply #62 on:** February 14, 2016, 01:03:09 am »

Oh it is true in part, Q17 is really 17 in the drawings.
Q18 that I show in the photo (Sorry) is actually Q19, I apologize to my friend, my eyes already are giving signs of aging

SAUL BRITTO · « **Reply #63 on:** February 14, 2016, 01:11:38 am »

In the drawings I see Q19 but on the schematic no.

SAUL BRITTO · « **Reply #64 on:** February 14, 2016, 01:30:11 am »

Q17 was that metallic I replaced and Q18 is a small transistor as a BC548 in your way.

rf+tech · « **Reply #65 on:** February 14, 2016, 02:22:54 am »

Saul,

No problem, my eyes are likely much worse. Sometimes it is easy to get lost between schematics and boards. Some of what I work on has no schematics available and still I manage to repair everything.

An observation about Q19, it is shown in figure 7-8 "Schematic 16 Replacement." Look just to the right of U6.

You are making good progress.

RF+ Tech

SAUL BRITTO · « **Reply #66 on:** February 14, 2016, 02:38:43 am »

Thank you rf+tech for your help and your time and patience.I am back to electronic after a long time out.
I am a bit oxidized, rusty!

SAUL BRITTO · « **Reply #67 on:** February 14, 2016, 03:31:10 am »

Yes rf+tech I found Q19 on the page 117 near to U2 main trig amp.

SAUL BRITTO · « **Reply #68 on:** February 14, 2016, 05:29:03 am »

rf+tech I really think that the tripler is lowering the HV circuit, is there any danger if disconnect it's ground pin?

rf+tech · « **Reply #69 on:** February 14, 2016, 02:44:26 pm »

Saul,

Disconnecting the ground pin on a HV tripler sounds like a very good way to inflict more damage on this scope. What is your expectation in taking such a risk?

Even if you manage to get the HV up to spec, there will be nothing to see on the screen.

Why?

Because the vertical deflection amplifier is forcing the beam off screen. Fix this first.

Does the vertical imbalance exist at the output of A3A1?
If so, have you disconnected the A3 preamp output from the A17 input and checked the A3 output to see if the imbalance is still present?
If so, have you checked to see if some input to the A3A1 is forcing the output out of balance?
If the A3A1 is defective and a replacement is not economical, why bother fixing the HV?
What good is a scope with working HV if the vertical amp is beyond repair and cannot bring the beam on screen?

Jumping to conclusions, jumping from one problem to another is not only poor troubleshooting technique, it makes far greater difficulty for people to follow and be of assistance.

Good troubleshooting technique stays focused on one problem at a time, makes lots of measurements from which to draw logical conclusions, checks and double-checks anything that appears to defy expectations then splits circuits in half to further isolate individual stages.

RF+ Tech

SAUL BRITTO · « **Reply #70 on:** February 14, 2016, 04:43:20 pm »

I was thinking about short on the tripler. But I did it and have not changed anything, the voltage did not rise If there is a problem in tripler will be open diod.

SAUL BRITTO · « **Reply #71 on:** February 14, 2016, 04:55:47 pm »

Quote from: rf+tech on February 14, 2016, 02:44:26 pm

Saul,

Disconnecting the ground pin on a HV tripler sounds like a very good way to inflict more damage on this scope. What is your expectation in taking such a risk?

Even if you manage to get the HV up to spec, there will be nothing to see on the screen.

Why?

Because the vertical deflection amplifier is forcing the beam off screen. Fix this first.

Does the vertical imbalance exist at the output of A3A1?
If so, have you disconnected the A3 preamp output from the A17 input and checked the A3 output to see if the imbalance is still present?
If so, have you checked to see if some input to the A3A1 is forcing the output out of balance?
If the A3A1 is defective and a replacement is not economical, why bother fixing the HV?
What good is a scope with working HV if the vertical amp is beyond repair and cannot bring the beam on screen?

Jumping to conclusions, jumping from one problem to another is not only poor troubleshooting technique, it makes far greater difficulty for people to follow and be of assistance.

Good troubleshooting technique stays focused on one problem at a time, makes lots of measurements from which to draw logical conclusions, checks and double-checks anything that appears to defy expectations then splits circuits in half to further isolate individual stages.

RF+ Tech

Ok I will make these tests.

SAUL BRITTO · « **Reply #72 on:** February 14, 2016, 05:01:08 pm »

I bought this scope very cheap just for remove your vertical skills,I have an 1740A with a problem in vertical skill
And was this my intention.But, I thought it was worth trying to fix the 1741A,and in fact I did not even look right if it is fully compatible skills.

SAUL BRITTO · « **Reply #73 on:** February 14, 2016, 05:03:37 pm »

Really you're right about the sequence analysis

rf+tech · « **Reply #74 on:** February 14, 2016, 06:27:05 pm »

Sual,

Maybe what we learn about the 1741 vertical problem will help repair the 1740 vertical problem.

I have been scrolling around in the 1741 manual and see there is a second schematic for A3 located five pages past the first schematic. This is figure 8-21 on page 8-29 and shows where the +/- 12 Volt regulators are located.

Perhaps you have been referring to Q17 and Q18 on A3, while I have been referring to Q17 and Q18 on A17. This has added to the confusion of finding an NPN in place of a PNP. The physical placement of Q17 and Q18 on the A3, close to U2 seems to match your photo. So yes, we have not been talking about the same board.

On the principle that measurements made with incorrect supply voltages are themselves incorrect and lead to incorrect conclusions, let's see why there is +/- 14.2 Volts where there should be +/- 12 Volts.

Looking at the A3 schematic, R123 and R124 bias the base of Q20 at +12.1 Volts. Q20 emitter and Q19 base should be about 0.6 Volts higher, +12.7 Volts. The emitter of Q19 should be about 0.6 Volts lower than the base, +12.1 Volts.

The -12 Volt regulator is a mirror of the +12 Volt regulator.

Let's see why both of these are not working correctly, before going ahead with the vertical deflection problem.

RF+ Tech

SAUL BRITTO · « **Reply #75 on:** February 14, 2016, 08:30:12 pm »

Is about this your comment?When you say: Does the vertical imbalance exist at the output of A3A1?
If so, have you disconnected the A3 preamp output from the A17 input and checked the A3 output to see if the imbalance is still present?
If so, have you checked to see if some input to the A3A1 is forcing the output out of balance?
If the A3A1 is defective and a replacement is not economical, why bother fixing the HV?
What good is a scope with working HV if the vertical amp is beyond repair and cannot bring the beam on screen?

SAUL BRITTO · « **Reply #76 on:** February 14, 2016, 08:33:46 pm »

In CR29 and CR30 I found a low resistence,where is marked 12V I get a small variation changing Position.In one channel is around 0.3 V on the other almost nothing it's stoped in 12,1V

SAUL BRITTO · « **Reply #77 on:** February 14, 2016, 09:08:31 pm »

Yes on the anode of diode CR27 I get 14.97V and on the collector of Q19 14.2V. 14.97-0.7 of diode= 14.2 ok?
On the base 12.7 and emmiter 12.01. 12.7-0.6 (base emmiter)= 12.01. Correct?
This is that I get here.

SAUL BRITTO · « **Reply #78 on:** February 14, 2016, 09:10:25 pm »

If you are not so experienced I think it would here turn a Babylonian tower

SAUL BRITTO · « **Reply #79 on:** February 14, 2016, 09:19:22 pm »

You remember,that one in short? Was Q17, +12 -12 are ok.I replaced Q17 with an original one.

rf+tech · « **Reply #80 on:** February 14, 2016, 09:47:13 pm »

Quote

In CR29 and CR30 I found a low resistence,where is marked 12V I get a small variation changing Position.In one channel is around 0.3 V on the other almost nothing it's stoped in 12,1V

I don't understand about these voltage measurements - from where to where?

The back to back diodes prevent the *differential* voltage from exceeding about 1.2 Volts - as measured directly across the two outputs. When this preamp is working properly, with a meter connected across the two outputs, the vertical position control should swing this voltage from +0.6 Volts, through zero Volts and to -0.6 Volts. By adjusting the vertical position control for zero volts - balanced output - the beam will be almost exactly centered.

If the series combination of R64, R65 and R66 in parallel with the diodes is close only several hundred Ohms, the diode test reading will not be reliable.

Quote

You remeber,that one in short? Was Q17, +12 -12 are ok.I replaced Q17 for an original one.

This is where we were Babel-ing on about Q17 in two different places. I was looking at the A17 and you were looking at the A3.

Quote

If you are not so experienced I think it would here turn a Babylonian tower

I can Babel with the best, I do this professionally in my own business - and repair things too.

RF+ Tech

SAUL BRITTO · « **Reply #81 on:** February 14, 2016, 10:00:59 pm »

Measuring in CR 29 and CR30 Vertical output, I get a variation of -403mV to +500mV,in both channels.

rf+tech · « **Reply #82 on:** February 14, 2016, 11:47:30 pm »

Quote

Measuring in CR 29 and CR30 Vertical output, I get a variation of -403mV to +500mV,in both channels.

That is good to see. Set this to close to zero Volts, reconnect the A3 output to the A17 input and let's measure the voltage from the collector of Q17 to the collector of Q18 on the A17. It should be close to zero Volts here and move positive/negative with the vertical position control. Set the vertical position back to zero Volts.

Then proceed to measure from the cathode of VR2 to the cathode of VR3. The same positive/negative swing should be measured here, but with much greater voltage range. Again, set the vertical position control for zero Volts.

Each point where the voltage can be set to zero, the two halves of the differential amplifier will be balanced. When the output across the deflection plates can be set to zero Volts, we will know the beam will be very close to the center of the screen.

Let's see how this goes.

SAUL BRITTO · « **Reply #83 on:** February 15, 2016, 12:25:57 am »

rf+tech,when I put a probe in X1 to channel B Using CAL 1V at .1V scale I get around 0.6 Volts pp, in other scope, after delay line on the input of that power vertical circuit,when I put position full left it shows 0.2V at the other scope and when I put full right it goes to 0.2V too.

rf+tech · « **Reply #84 on:** February 15, 2016, 12:45:55 am »

Saul,

For now, it is not important about the difference between the two scopes. Our concern is only with no signal, will the difference adjust to zero?.

Set the input coupling to GND and continue with the procedure above.

Once we know that the differential output can be balanced to zero Volts all the way to the deflection plates, then we can evaluate this difference between the two scopes.

RF+ Tech

SAUL BRITTO · « **Reply #85 on:** February 15, 2016, 12:52:40 am »

Are that diodes a kind of 1n4148? it shows 13.8 to -36.4. I did all that tests and very near to 0V, i can but, it's very critical I just can 0.03V,ok?

SAUL BRITTO · « **Reply #86 on:** February 15, 2016, 12:56:44 am »

rf+tech> Ok, it was the same way with GND connected,I get 0V and the other voltages above.

SAUL BRITTO · « **Reply #87 on:** February 15, 2016, 01:10:57 am »

Guys please sorry for my crazy english!

rf+tech · « **Reply #88 on:** February 15, 2016, 01:45:40 am »

Saul, your English is not a problem. My problem is guessing about missing details to be certain we are talking about the same thing, the same place and the same type of measurement.

Quote

If that diodes are as 1n4148 it shows 13.8 to -36.4.

Guessing that 13.8 to -36.4 is from one diode to ground?

Quote

I did all that tests and very near to 0V,

So the difference across the deflection plates can be set to zero, then the entire vertical amplifier is working okay, except maybe the gain may be wrong.

Quote

it's very critical it was 0.03,ok?

0.03 Volts is close enough to zero and that is very good.

So you are ready for the next problem, yes?

SAUL BRITTO · « **Reply #89 on:** February 15, 2016, 01:50:13 am »

OH sorry it was to measure cathode to ground? I did it cathode to cathode,but I can do it to ground.Please confirm that I did it wrong.

SAUL BRITTO · « **Reply #90 on:** February 15, 2016, 01:56:36 am »

Measuring to ground it is 43.9 to 70 Volts in one diode. The other was 32.7 to 50.0 Volts

SAUL BRITTO · « **Reply #91 on:** February 15, 2016, 02:03:32 am »

If I made it wrong I interpreted you text in bad way,when you said: That is good to see. Set this to close to zero Volts, reconnect the A3 output to the A17 input and let's measure the voltage from the collector of Q17 to the collector of Q18 on the A17. It should be close to zero Volts here and move positive/negative with the vertical position control. Set the vertical position back to zero Volts.

Then proceed to measure from the cathode of VR2 to the cathode of VR3. The same positive/negative swing should be measured here, but with much greater voltage range. Again, set the vertical position control for zero Volts.

Each point where the voltage can be set to zero, the two halves of the differential amplifier will be balanced. When the output across the deflection plates can be set to zero Volts, we will know the beam will be very close to the center of the screen.

Let's see how this goes.

"let's measure the voltage from the collector of Q17 "to the collector of Q18 on the A17."

It was to measure the difference between the two collectors,the two probes on the collectors?

rf+tech · « **Reply #92 on:** February 15, 2016, 02:13:24 am »

Quote

OH sorry it was to measure cathode to ground? I did it cathode to cathode,but I can do it to ground.Please confirm that I did it wrong.

Thank you for clarifying. Both types of measurement are valid.

Maybe my use of the word differential is part of the problem. Push-pull may be easier understand. The deflection plates push and pull the beam, depending on the voltage across the deflection plates and the polarity of one plate to the other plate. The actual voltage from one plate to ground is of lesser importance.

Here is a thought experiment: with only one meter, measure the voltage from one deflection plate to ground. Next measure the other plate to ground. Then adjust the vertical center control, measure one plate voltage to ground, then the other, back and forth until both plates are at the same voltage. Now measure the voltage across the two plates and it should be close to zero Volts. This is the condition required for the beam to be in the middle of the screen.

See how much easier it is to simply place the meter across both sides of a push-pull amplifier and adjust the vertical center control for zero Volts? This is why I am saying the voltage to ground is not important. What is most important is the difference between the two sides.

--

Okay, I am very slow to write my thoughts.

Quote

It was to measure the difference between the two collectors,the two probes on the collectors?

Yes, this is the correct way. Please, if there is anything you do not understand, ask. I do not want you to feel frustrated.

SAUL BRITTO · « **Reply #93 on:** February 15, 2016, 02:23:45 am »

Thank you rf+tech! When you says: adjust de vertical center,you want to say that adjust ,on the board, not the position,right?

SAUL BRITTO · « **Reply #94 on:** February 15, 2016, 02:31:37 am »

I see on the board polarity balance... This is on the shield cover with drawings.

rf+tech · « **Reply #95 on:** February 15, 2016, 02:34:30 am »

Quote

When you say adjust de vertical center,you want to say that adjust on the board, not the position,right?

No, adjust the "vertical position" control on the front panel. Think of how the vertical position control works on a good scope. The beam moves up or down with the vertical position control.

The adjustments on the board should not be altered yet. This may add more confusion.

Please allow me more time to write.

SAUL BRITTO · « **Reply #96 on:** February 15, 2016, 02:36:29 am »

Oh my friend you have all the time of the word! Relax. Maybe I am the nervous here !

SAUL BRITTO · « **Reply #97 on:** February 15, 2016, 02:50:43 am »

rf+tech > near to zero I can, around 0.053mV.

SAUL BRITTO · « **Reply #98 on:** February 15, 2016, 02:53:27 am »

I am measuring with a keysight DMM but has a fluke 179 here...

SAUL BRITTO · « **Reply #99 on:** February 15, 2016, 02:58:30 am »

Ok I did the work. I can measure 0.0V on the two channels but with de position a bit to left, around 20%.

rf+tech · « **Reply #100 on:** February 15, 2016, 03:08:34 am »

Quote

I can measure 0.0V on the twa channels but with de poisition a bit to left around 20%.

Great!

No concern about the 20%. When the alignment procedure in the manual is performed, this error will be corrected.

Quote

near to zero I can, around 0.053mV.

If it will help to understand, the deflection plates have a sensitivity expressed in Volts per centimeter. A guess, maybe 10 Volts deflects the beam by 1 cm. One Volt will deflect the beam 1 mm. 0.1 Volt will deflect the beam 0.1 mm. 0.053 Volts will deflect the beam .053 mm. Can you see that small?

SAUL BRITTO · « **Reply #101 on:** February 15, 2016, 03:29:11 am »

Good! But I don't know if you remember: this scope don't have a visible trace.I said to you: it has just 2.8 kV when it was to have at least 5kV.

SAUL BRITTO · « **Reply #102 on:** February 15, 2016, 03:32:06 am »

I don't know right now who is the culprit, maybe fllyback or tripler ou another component in HV or LVPS.Despite I did measure all the voltages on the LVPS and all that was correct.unless a mistake my.

SAUL BRITTO · « **Reply #103 on:** February 15, 2016, 03:34:19 am »

I did see that some rectifier bridges,are very hot.I dont know the regimen of those rectfiers.

rf+tech · « **Reply #104 on:** February 15, 2016, 03:41:58 am »

Yes, I remember the tripler may be defective. The manual says the CRT cathode voltage should be -2295 Volts. Can you measure this safely?

If this voltage is correct, then the tripler is defective. But do not worry about it, I have an idea.

Quote

I did see that some rectifier bridges,are very hot.I dont know the regimen of those rectfiers.

What CR number on the power supply schematic?

SAUL BRITTO · « **Reply #105 on:** February 15, 2016, 04:03:57 am »

I measured The cathode V and,it was around -1850V.What is CR? Is the part number of CRT?

SAUL BRITTO · « **Reply #106 on:** February 15, 2016, 04:19:45 am »

I do have a RCA 56kV probe. I will measure the cathode again.

SAUL BRITTO · « **Reply #107 on:** February 15, 2016, 04:29:39 am »

rf+tech> It shows me exactly -1832V.

SAUL BRITTO · « **Reply #108 on:** February 15, 2016, 04:57:44 am »

Ah, ok! CR= rectifiers. I think most.

rf+tech · « **Reply #109 on:** February 15, 2016, 04:59:14 am »

Quote

What is CR? Is the part number of CRT?

CR1, CR2, CR3, CR4, CR5, CR6, CR7 are the bridge rectifiers on the power supply board schematic.

Quote

I did see that some rectifier bridges,are very hot.I dont know the regimen of those rectfiers.

What is the CR number of the hot rectifier bridges on the power supply board?

Quote

It shows me exactly -1832V

This cathode voltage is too low. Measure the +120 Volts on the HV power supply. And check that the "Deep Erase" switch on the rear panel is set to "Normal."

About the -1832 Volts, here is what I think. Look at the HV power supply schematic. See where the tap on the HV transformer secondary (pin 7) is less turns than the end of the secondary that becomes -2295 Volts with CR3?

If the +120 Volts is good, and the tripler is defective, the tripler may be loading the HV transformer and pulling the CRT cathode voltage down. Disconnect the lead to the tripler, from this pin 7 of the HV transformer. Measure the CRT cathode voltage again. Is it still -1832 Volts or is it now close to -2295 Volts?

SAUL BRITTO · « **Reply #110 on:** February 15, 2016, 05:42:28 am »

rf+tech is normal the UNG 15V with 24V? I know that is unregulated but...As I don't know very well this circuit...

SAUL BRITTO · « **Reply #111 on:** February 15, 2016, 05:49:35 am »

rf+tech the 120V measuring on the botton of board on the connector that goes to HV is with 123V the pin oh tripler I will do it later,because I'm almost dead tired!

SAUL BRITTO · « **Reply #112 on:** February 15, 2016, 05:51:12 am »

Here in Brazil: 2:50 until later. Thank you for all . have a good day.

SAUL BRITTO · « **Reply #113 on:** February 15, 2016, 04:42:10 pm »

rf+tech disconnecting the cable post-tripler and the GND will not be the same than disconnecting that one of pin 7?

rf+tech · « **Reply #114 on:** February 15, 2016, 05:58:12 pm »

Yes, it is the same. It is not safe. There may be an arc that damages other components or yourself.

Only if the wire to the tripler from the HV transformer is one piece without a solder or twist lock connection, should floating the tripler be attempted and only with great caution and very good insulation. In this case, be very very careful.

Here is a saying to think about:

There are old electricians, and there are bold electricians.
But there are no old, bold electricians.

SAUL BRITTO · « **Reply #115 on:** February 15, 2016, 09:45:55 pm »

Oh yes it's true!! But I wil do it as you said in another text,the correct way.I Preffer be an old not a bold.

SAUL BRITTO · « **Reply #116 on:** February 15, 2016, 10:43:10 pm »

rf+tech already managed to repair a tripler? It's possible to use another trilper as one tektronix in lacking of an original?

SAUL BRITTO · « **Reply #117 on:** February 15, 2016, 10:45:31 pm »

I know a guy here in my country that made it times ago. He fixed the tripler,was a philips one.

SAUL BRITTO · « **Reply #118 on:** February 15, 2016, 10:46:49 pm »

Look: http://www.py2bbs.qsl.br/pm3540.php

rf+tech · « **Reply #119 on:** February 15, 2016, 11:21:34 pm »

Saul,

Remember i said

Quote

But do not worry about it, I have an idea.

Yes, it is possible to build one yourself. Here is an application note by Vishay on just this subject:

http://www.vishay.com/docs/88842/anusingr.pdf

Yes, it should be possible use almost any other scope tripler and if you are careful, you may be able to excavate and repair the HP tripler.

There are many possibilities. First, tell me about the test results.

RF+ Tech

SAUL BRITTO · « **Reply #120 on:** February 15, 2016, 11:30:59 pm »

rf+tech I was seeing a french video abouT this scope (hp) and it was fenomenal for your time.
Ok, soon I tell you the result.

SAUL BRITTO · « **Reply #121 on:** February 15, 2016, 11:53:48 pm »

rf+tech beeing it a tripler, that multiplies x3 then, the flyback generates around 1600V?

Sorry for this idiot question but,is just to be sure about a small question: "sparks," in case of disconnection of pin 7.

rf+tech · « **Reply #122 on:** February 16, 2016, 12:21:07 am »

Yes, when the HV circuit is able to supply 2295 Volts to the CRT cathode.

Can the wire to the tripler be disconnected at the HV power supply board? Or must the wire be disconnected from the tripler?

SAUL BRITTO · « **Reply #123 on:** February 16, 2016, 01:04:57 am »

it must to be disconnected from the board,has a pin on the botton of the board connected to the flyback with a kind of thermo-retractil insulator.

SAUL BRITTO · « **Reply #124 on:** February 16, 2016, 01:15:34 am »

I just can disconnect the tripler on that connection of anode of tube and the ground pin as I said before.

SAUL BRITTO · « **Reply #125 on:** February 16, 2016, 01:43:10 am »

courageously I disconnected the cable from the anode and the earth and it continues measuring -1832V.

rf+tech · « **Reply #126 on:** February 16, 2016, 02:06:34 am »

This is interesting. My best guess is someone tried to "fix" the original problem shown in your video by adjusting the HV.

Always, always mark any control before turning, so it can be put back in the original place.

Now it is right to try HV ADJ R38, to see if the HV can be increased to -2295 Volts. If it only goes less, tell me what the measurement is.

Of course, reconnect the tripler first.

SAUL BRITTO · « **Reply #127 on:** February 16, 2016, 02:16:48 am »

Online rf+tech really,all the electrolityc capacitors was replaced in all the PS. Power oscillator is with strange behavior on DMM.
I will back with more.

SAUL BRITTO · « **Reply #128 on:** February 16, 2016, 02:37:30 am »

On the HV ADJ I can -1922 maximum on the cathode test point.

rf+tech · « **Reply #129 on:** February 16, 2016, 02:47:31 am »

Okay, I would put this back to -1832 Volts.

How dirty is the pc board around CR3, C6, R11, C7, R12 and all components that connect to the cathode circuit? Could there be leakage around these parts?

Look closely at R13, 30 MOhm resistor. If there is electrical leakage across R13, the HV will be low and not adjust. Better to remove R13 and measure it.

SAUL BRITTO · « **Reply #130 on:** February 16, 2016, 02:51:16 am »

I found a resistor of 560 Ohms measuring 598 Ohms,just need to know what is it's connection. I don't know ifit is R18 or R19 on the pin 6 of IC U1.Or that one connected to CR3 it seems R11.

SAUL BRITTO · « **Reply #131 on:** February 16, 2016, 03:06:44 am »

Quote from: rf+tech on February 16, 2016, 02:47:31 am

Okay, I would put this back to -1832 Volts.

How dirty is the pc board around CR3, C6, R11, C7, R12 and all components that connect to the cathode circuit? Could there be leakage around these parts?

Look closely at R13, 30 MOhm resistor. If there is electrical leakage across R13, the HV will be low and not adjust. Better to remove R13 and measure it.

The board is very clean in all areas.

SAUL BRITTO · « **Reply #132 on:** February 16, 2016, 03:15:16 am »

R13 is 29.99M

rf+tech · « **Reply #133 on:** February 16, 2016, 03:36:46 am »

Good information on R13 and very clean pc board.

The voltage on U1 pin 6 may tell something.

SAUL BRITTO · « **Reply #134 on:** February 16, 2016, 03:56:56 am »

Quote from: rf+tech on February 16, 2016, 03:36:46 am

Good information on R13 and very clean pc board.

The voltage on U1 pin 6 may tell something.

R21 1M on pin 6 is more than 20% altered,it measures 1.260M

SAUL BRITTO · « **Reply #135 on:** February 16, 2016, 04:24:23 am »

rf+tech at the pin 6 of U1 i have -2.6V.

rf+tech · « **Reply #136 on:** February 16, 2016, 02:46:59 pm »

Quote

rf+tech at the pin 6 of U1 i have -2.6V.

This is good and shows that the feedback loop is regulating properly.

But, this tells me the RCA HV probe calibration may be not be good.

Since U1 pin 2 voltage is zero (returned to ground via R24), the voltage at U1 pin 3 must also be zero.

Therefore, the two currents through the resistor dividers must also sum to zero.

-1832 Volts / 29.3 MOhms = -62.5 uA, derived from the -HV

If the curent through R13 is correct, then the current through R36, R38 and R37 must also be the same magnitude, but opposite polarity. So we solve to find the total resistance required for +62.5 uA from +15 Volts:

15 Volts / 62.5 uA = 240 kOhms

The total resistance of R36, R38 and R37:

182 kOhms + 10 kOhms + 9.09 kOhms = 201 kOhms, with R38 at maximum
201 kOhms - 5 kOhms = 196 kOhms R38 mid control

Now we calculate the current from +15 Volts:

+15 Volts / 196 kOhms = +76.5 uA

This must be balanced by the same current of the opposite polarity from -HV:

-76.5 uA * 29.3 MOhms = -2242 Volts

This shows that the -HV must really be -2242 Volts and shows that the RCA HV probe cannot be trusted.

SAUL BRITTO · « **Reply #137 on:** February 16, 2016, 04:37:46 pm »

rf+tech Ok. That probe is really bad then.Despite I've measured some other voltages with it and was ok,voltages of 220V or below. In this case what do you think that can be the defect?

SAUL BRITTO · « **Reply #138 on:** February 16, 2016, 04:49:16 pm »

I was thinking about an overload caused by any things as tube,can it be possible?

SAUL BRITTO · « **Reply #139 on:** February 16, 2016, 04:51:52 pm »

But with this news I am a bit confuse.If the cathode V is right maybe the anode V is right too.

SAUL BRITTO · « **Reply #140 on:** February 16, 2016, 04:59:19 pm »

rf+tech I do have here some VTVM in good condictions it can measure 1500V and it's input impedance is 11M in DC skill. Can I double or duplicate the impedance with another resistor of 11M in series? I think there is a way to resolve this.Of coarse: My hand the probe will not see

SAUL BRITTO · « **Reply #141 on:** February 16, 2016, 05:42:56 pm »

I did this question before I don't know if you remember: It's normal the 15V Unreg be 24V? It's 24V on the PS board and HV board.

rf+tech · « **Reply #142 on:** February 16, 2016, 11:20:33 pm »

Saul,

I'll try to answer some things.

Quote

It's normal the 15V Unreg be 24V? It's 24V on the PS board and HV board.

Depending on your mains voltage, if it is higher than normal, then yes, the unregulated 15 will be high. This really does not affect the HV output, U1 compensates for any deviation on the HV output, or the input, by adjusting the DC voltage to the base of the power oscillator transistor. Since U1 is the regulator, the 15 volts to the power oscillator does not need to be regulated.

Quote

But with this news I am a bit confuse.If the cathode V is right maybe the anode V is right too.

More math: The HV probe error is 2242 - 1832 = 410 Volts low.

410 / 2242 = 18.3%

2800 * 18.3% = 512 Volts

2800 + 512 = 3312 Volts from the tripler

3312 / 2 = 1656 Volts into the tripler

1656 * 3 = 4968 Volts out of the tripler.

4956 Volts is "close enough" to 5 kV, yes?

Looks like the tripler is only a doubler, it is defective.

Quote

That probe is really bad then.Despite I've measured some other voltages with it and was ok,voltages of 220V or below. In this case what do you think that can be the defect?

Defective may be a bit strong. 18.3% error is excessive. The probe reading ok at 220 V may indicate the high value resistor inside has some voltage-dependent non-linearity. If this is true then even the 18.3% figure may in fact need to be increased with higher voltages, such as at 2.8 kV. Post a photo of the probe and how it is connected to your meter. I am guessing this probe is a color TV HV probe and it is being used with a DVM? If this is true, the probe is intended to work into an 11 MOhm VTVM, Using this probe with a 10 MOhm DVM introduces an error immediately. But I am guessing because I do not know any of the important details to make a good conclusion.

I have experience working with feedback resistances from 2 GOhms (2*10^9) to 2 TOhms (2*10^12). This is an art all of its own, just as with RF and microwaves. There may be some hope for your probe, but I need to see it first and know the details about it.

RF+ Tech

SAUL BRITTO · « **Reply #143 on:** February 17, 2016, 01:28:54 am »

Hi rf+tech Good night. Thank you. Yes looks like the probe was not so good seems it was a bad contact and really I WAS USING A DMM! wow! But I has some VTVM like the heathkit IM-10 RCA-Voltohmyst etc. The probe is an old RCA WG-297

SAUL BRITTO · « **Reply #144 on:** February 17, 2016, 02:11:46 am »

rf+tech can I measure with a VTVM directly with the HV probe,without that 11M one?

SAUL BRITTO · « **Reply #145 on:** February 17, 2016, 02:40:31 am »

rf+tech Using a VTVM on the post tripler I can measure 5kV now

SAUL BRITTO · « **Reply #146 on:** February 17, 2016, 02:46:38 am »

Including I can hear a noise of HV coming from tripler when I touch with the HV probe inside the connector even when the scope is off.

SAUL BRITTO · « **Reply #147 on:** February 17, 2016, 03:12:53 am »

Where is marked I can measure exactly 5kV,can this be a gridd not polarized or tha HV post-tripler cable with some kind of problem? Did you see any thing like this? Times ago I remember not exactly if in same way a problem on HV connection of anode of a tv tube, the contact was oxidized.

rf+tech · « **Reply #148 on:** February 17, 2016, 03:30:34 am »

Saul,

Quote

rf+tech

My memory is fuzzy, the Heathkit and RCA VTVMs were 10 MOhm at the front panel connector and have an additional 1 MOhm resistor in the probe body. The over-all input resistance is 11 Megohms.

The RCA WV-98A manual states:

Quote

DC voltages as high as 50,000 Volts can be measured directly by the WV-98A when the WG-289 High-Voltage Probe is used. The probe uses the WG-206 Multiplier Resistor, having a value of 1090 megohms, to present an overall voltmeter input resistance of 1100 megohms.

Quote

Using a VTVM on the post tripler I can measure 5kV now

Well, this is good news, indeed.

And you have learned that improper results and incorrect conclusions occur when using HV probes with the wrong meters.
You may ask yourself "how did I know your mistake?"

Quote

I can hear a noise of HV coming from tripler when I touch with the HV probe inside the connector even when the scope is off.

There may not be a bleeder resistor present in the tripler to discharge the output filter capacitor. When the probe tip approaches the connector, the air will ionize and a small sizzle noise will be heard. Leaving the probe in contact should show the voltage falling, as the probe discharges the output capacitor. Perfectly normal.

Quote

can this be a gridd not polarized

I think what you are saying is that the grid may be in cutoff, so there is no beam from the cathode. This is what I believe to be the *next* problem. I do not think oxidation of the HV anode is the problem. Really, how can a little oxidation stop 5000 Volts?

Next, the cathode and grid voltages need to be measured, to see if the CRT is cutoff. This should be done with the HV probe and VTVM because both are at high voltages.

RF+ Tech

SAUL BRITTO · « **Reply #149 on:** February 17, 2016, 03:36:53 am »

rf+tech I can read -2450V on the TP5 of gridd,is it ok? I do not see at the schematic the indication of voltage for that.

SAUL BRITTO · « **Reply #150 on:** February 17, 2016, 04:04:57 am »

You may ask yourself "how did I know your mistake?" >> The masters are like poets, they know and can all the things.
rf+tech you are a big professional and I hope be a good disciple.

rf+tech · « **Reply #151 on:** February 17, 2016, 05:10:17 am »

Saul,

Quote

I can read -2450V on the TP5 of gridd,is it ok?

By itself, this measurement has little meaning. Both measurements must be considered together. What is the cathode voltage?

Thank you for the good compliments. I am glad to count you as a follower.

RF+ Tech

SAUL BRITTO · « **Reply #152 on:** February 17, 2016, 05:19:54 am »

rf+tech I can read 2.4kV on the cathode. Seems I have a difference of -50 Volts gridd to cathode.

rf+tech · « **Reply #153 on:** February 17, 2016, 09:06:07 pm »

Saul,

Quote

I can read 2.4kV on the cathode. Seems I have a difference of -50 Volts gridd to cathode.

The -50 Volts grid to the cathode appears to be normal cutoff. The next circuit to check is the gate amplifier, to see if the gate pulse is missing.

First, it is very important from now on to set front and rear panel controls exactly as specified in Section V, paragraph 5-12. Do not change any of these control settings, except as the manual instructs in a specific procedure.

Many measurements are affected by the front and rear panel controls. Any measurements made with controls not set as instructed can be considered invalid, cause confusion and waste time. Read paragraphs 8-71 through 8-76 carefully.

The Gate Amplifier circuit should be checked as described in paragraph 5-19. This requires another working oscilloscope and 10:1 probe. The 10:1 probe must be properly compensated using the built-in 1 kHz signal source.

Follow steps in 5-20a and 5-20b. At step 5-20c, do not make any adjustment at this time, only measure the peak amplitude of the gate signal. Tell me the measurement, or if the gate signal is not present. Continue with step 5-20f and 5-20g.

If the gate signal is missing, paragraph 8-86 offers some tips about failure.

RF+ Tech

SAUL BRITTO · « **Reply #154 on:** February 17, 2016, 09:26:10 pm »

rf+tech I was right now looking the gate circuit it has a signal that goes to HV board and seems that varies with the sweep frequency,when is low it is low too. Ok I know what is the procedure to accomplish the measures.

SAUL BRITTO · « **Reply #155 on:** February 17, 2016, 10:05:53 pm »

rf+tech CONV disengaged means convetional mode off?

SAUL BRITTO · « **Reply #156 on:** February 17, 2016, 10:14:01 pm »

rf+tech it's ready!

rf+tech · « **Reply #157 on:** February 17, 2016, 10:19:07 pm »

Saul,

You mean the scope is now working in conventional mode, with a trace?

I was about to post more troubleshooting steps...

RF+ Tech

SAUL BRITTO · « **Reply #158 on:** February 17, 2016, 10:45:18 pm »

No trace.I said ready for troubleshootings. I just need you explain a small thing to me: where or what is VOLTS/DIV vernier (Channel A and B) CAL detent (Fully Cw) I am with a small doubt about this. I just see one knob as vernier and don't understand where it is with Channel A and B. Vernier appears twice have to be adjusted to CALL, call detent (Fully cw) and CAL so I did CAL

SAUL BRITTO · « **Reply #159 on:** February 17, 2016, 11:08:49 pm »

I already has another scope on the hand.

rf+tech · « **Reply #160 on:** February 17, 2016, 11:23:44 pm »

Quote

No trace.

Aw, I was ready to post my beer icon!

Photo showing verniers (if I did this right):

Quote

I said ready for troubleshootings.

Okay, the manual describes:

Quote

A protection circuit consisting of A15Q4, A15U2, A15Q5 is incorporated in the cathode circuit to prevent accidental burning of the CRT during deep erase operations, while turning the instrument on and off, and during quick power dropouts.

Check that Q4 does not stay on continuously, by measuring pin 1 of U2. If the voltage is about -13 Volts, then the LED in U2 is turned on, the output of U2 will turn on Q5 and the CRT will be cutoff.

Be very careful identifiying pin 1 of U2, the other side of U2 is -HV cathode potential.

Capacitor C18 should be checked. What about the filament in the CRT? Does the neck feel warm?

RF+ Tech

SAUL BRITTO · « **Reply #161 on:** February 17, 2016, 11:38:37 pm »

Ok. I have to put the knobs CAL on,where that red led lights?

SAUL BRITTO · « **Reply #162 on:** February 17, 2016, 11:42:11 pm »

U2 is the 6 pins IC that seems a optocoupler or is that in gate board? That in gate board appear as U1,maybe it's second section be U2...

SAUL BRITTO · « **Reply #163 on:** February 17, 2016, 11:46:09 pm »

rf+tech if CAL detent has to be Fully CW then it has to be off,rigth?

Sorry for those small questions it's because I want to do it right.

rf+tech · « **Reply #164 on:** February 18, 2016, 12:00:20 am »

Quote

I have to put the knobs CAL on,where that red led lights?

Yes, the red lights should be off. When the CAL knobs are turned full CW, the Volts/Div is CALibrated.
When the CAL knob is turned CCW, the Volts/Div is uncalibrated and the red light is on to remind.

Quote

U2 is the 6 pins IC that seems a optocoupler?

Yes, this is correct.

Quote

U2 is the 6 pins IC that seems a optocoupler?

Quote

Sorry for those small questions it's because I want to do it right.

Ah, gafanhoto, você está se tornando sábio como eu.

(Do you know the movie 'Kung Fu"?)

SAUL BRITTO · « **Reply #165 on:** February 18, 2016, 12:03:45 am »

If U2 is that 6 pins,pin 1 is -10.2V

SAUL BRITTO · « **Reply #166 on:** February 18, 2016, 12:06:55 am »

Ah, gafanhoto, você está se tornando sábio como eu.
(Do you know the movie 'Kung Fu"?)

Hey man this about gafanhoto I did not see but,will tell you later about the cat and the jaguar.

SAUL BRITTO · « **Reply #167 on:** February 18, 2016, 12:25:25 am »

I already see the filament and it lights and feel a bit hot that shield over it.

rf+tech · « **Reply #168 on:** February 18, 2016, 01:01:45 am »

Quote

If U2 is that 6 pins,pin 1 is -10.2V

This says that the LED inside U2 may be turned on when it should be off. To verify another way, measure the voltage drop across R45, 270 Ohms. The current through R45 and the LED will be Volts divided by 270, maybe 10 mA. But there should not be any voltage drop, no current and the LED inside U2 should be off.

The voltage on C18 should be very close to -15 Volts. This will keep Q4 turned off. If C18 is leaky/shorted, Q4 may be turned on, then U2 will disable the trace. If Q4 is shorted, U2 will disable the trace.

SAUL BRITTO · « **Reply #169 on:** February 18, 2016, 01:16:10 am »

I am trying to find C18 but can't. I see it on the schematic but on the boar looks like it isn't there,do you know it's location?

SAUL BRITTO · « **Reply #170 on:** February 18, 2016, 01:24:02 am »

I found that 270 Ohms resistor altered to 320 ohms.

rf+tech · « **Reply #171 on:** February 18, 2016, 01:26:21 am »

Quote

I am trying to find C18 but can't. I see it on the schematic but on the boar looks like it isn't there,do you know it's location?

Figure 8-17, page 8-20 chart says C18 is at grid "E4"

Quote

I found that 270 Ohms resistor altered to 320 ohms.

That is a problem, but not *the* problem.

SAUL BRITTO · « **Reply #172 on:** February 18, 2016, 01:28:57 am »

Seems the resistor 2700 ohms on the normal position do not works, right? It is altered to 3.200 ohms too.

SAUL BRITTO · « **Reply #173 on:** February 18, 2016, 01:35:25 am »

At my mind C18 was a electrolityc CAP but, it is more smart than a gafanhoto,was under any cables and is another kind of cap seems a mica cap.

SAUL BRITTO · « **Reply #174 on:** February 18, 2016, 01:42:06 am »

Across R45 I read around 4.2 mV

SAUL BRITTO · « **Reply #175 on:** February 18, 2016, 01:53:30 am »

Wow measuring the R45 I see 6.2 mV one lead to the other.Is this you want?

SAUL BRITTO · « **Reply #176 on:** February 18, 2016, 02:01:17 am »

6.2mV/320 Ohms (270) will this led work with this current?

SAUL BRITTO · « **Reply #177 on:** February 18, 2016, 02:05:59 am »

Is it 19uA or, am I confused?

rf+tech · « **Reply #178 on:** February 18, 2016, 02:09:13 am »

Quote

Seems the resistor 2700 ohms on the normal position do not works, right? It is altered to 3.200 ohms too.

Is this really 3200 Ohms (3.2 kOhms)? Maybe it is time to check your meter with some 1% precision resistors?

Quote

C18 ... seems a mica cap.

22 uF in mica will be about as large as the entire HV board. The parts list has the letters "TA" which indicates this is a Tantalum capacitor.

Quote

Across R45 I read around 4.2 mV

Okay, there is no current flowing through the LED in U2.
.0042 Volts / 270 Ohms = 15.5 uA. The LED should be off.
.0062 Volts / 320 Ohms = 19.3 uA.
The LED would need maybe 10 mA to turn on U2.

Move the Normal/Deep Erase to Deep Erase. This will turn on Q4 and the LED in U2. Now measure the voltage across R45.

With the scope turned off, some tests on the HV side of U2. Check zener diode VR3 (zener diodes like to fail shorted), diode-test Q5 for shorted and diode test U2 pins 5 to 6 for shorted.

Oh, yes, verify sweep at the deflection plates. Using another scope, check both horizontal deflection plates for the sweep ramp.

SAUL BRITTO · « **Reply #179 on:** February 18, 2016, 02:18:52 am »

The voltage over C18 is -11.2 V

SAUL BRITTO · « **Reply #180 on:** February 18, 2016, 02:20:47 am »

Is this really 3200 Ohms (3.2 kOhms)? Maybe it is time to check your meter with some 1% precision resistors?

no I said 320 Ohms (270).

SAUL BRITTO · « **Reply #181 on:** February 18, 2016, 02:28:48 am »

With deep erase on I read 0.2mV.

rf+tech · « **Reply #182 on:** February 18, 2016, 03:06:09 am »

Quote

The voltage over C18 is -11.2 V

This looks okay. With very low current, VR4 will be less than 11 Volts. 11.2 Volts minus 0.6 Volts for Q4 base-emitter = 10.6 Volts across VR4. I did not look closely at this.

Quote

no I said 320 Ohms (270).

Yes, but read again what you wrote earlier:

Quote

Seems the resistor 2700 ohms on the normal position do not works, right? It is altered to 3.200 ohms too.

2700 Ohms implies R43
270 Ohms implies R45.
Who is

So please explain "3.200 Ohms."
3.2 Ohms is 2696.8 Ohms less than 2700 Ohms.
I have to guess is this really Ohms or kOhms? I think this is 3200 Ohms (3.2 kOhms).

If your meter measures 270 Ohms as 320 Ohms, 15.6% higher, and measures 2700 Ohms as 3200 Ohms, also 15.6% higher --- then your meter may not be accurate. The meter needs to be checked with known good 1% resistors. It would be very unusual for all resistors in this HP scope to be 15.6% high.

Quote

With deep erase on I read 0.2mV.

Hmm. This is only 625 uA, I don't think U2 can turn on with this low current.
What part number appears on U2? The parts list shows 1990-0607.
What are the emitter, base and collector voltages on Q4, in normal and deep erase?

SAUL BRITTO · « **Reply #183 on:** February 18, 2016, 03:19:07 am »

I measured with three meters and was all near basicly the same thing.The resitor of 2700 Omhs is 3.000 Right now
Maybe because I removed U2 and replaced it the pins was very dirty,I don't know...
I did look if was a short in collector and emmiter of U2 but, no.

SAUL BRITTO · « **Reply #184 on:** February 18, 2016, 03:27:18 am »

The part number is 199006077812

SAUL BRITTO · « **Reply #185 on:** February 18, 2016, 03:34:45 am »

Normal

Base= -11.23V
Emmiter= -10.63V
Collector= -10.64V

Deep erase

Base= -0.6
Collector= -13.37
Emitter= -3.7

SAUL BRITTO · « **Reply #186 on:** February 18, 2016, 03:52:34 am »

Man! I think this resistor of 68K don't smell good...

SAUL BRITTO · « **Reply #187 on:** February 18, 2016, 04:07:24 am »

The 68k is 76.6k Omhs

rf+tech · « **Reply #188 on:** February 18, 2016, 04:49:19 am »

The voltages on Q4 show that my interpretation of Q4 on/off is reversed.

These old HP schematics where transistors are drawn both "right side up" and "up side down" always make my head hurt.

The most common convention is to place the transistor terminal, emitter of PNP and collector of NPN at the top where positive voltage is also at the top. Negative voltages and transistor terminals connected to negative voltages are drawn lower. Here is an example where PNP transistors are drawn two different ways in the same schematic. Crazy. This just makes it harder to understand the circuit.

After drawing this circuit on paper the "proper" way, it is obvious at a glance how Q4 works. When the scope is off, the -15 Volt supply is at zero. C18 discharges through R44. When switch S1 is in "normal" and the scope is first turned on, C18 looks like a short and holds Q4 off. R44 charges C18 with current toward -15 Volts. When the voltage on C18 exceeds VR4 plus the base-emitter drop of Q4, about -11.2 Volts, Q4 turns on.

When "deep erase" connects R45 to ground through switch S1, C18 is discharged and Q4 is turned off.

In "normal" with Q4 turned on, current through R45 turns on the LED in U2 and the output transistor of U2 also turns on. This action turns on Q5 and shorts VR3.

VR3 causes the CRT cathode to be 100 Volts more positive than the grid, the CRT is more deeply cutoff. This protects the CRT from burning when the scope is turned on and turned off, or when electric power is lost momentarily and comes back in very quickly.

After a short delay by C18 and R44, the protection is released.

Based on all the voltage measurements, I think the problem is the LED inside U2 has failed open circuit. The output transistor inside U2 cannot turn on and the extra 100 Volts keeps the CRT deeply cutoff.

The single most valuable measurement is the voltage drop across R45 (270 Ohms). Using a 4N25 datasheet as a reference, 10 mA of LED forward current is used to describe the transfer characteristics. Data found for U2 part number 1990-0607 is too minimal to be 100% conclusive, but 625 uA seems not sufficient to turn on U2.

4N25 is not suitable for replacing U2. A good parametric search is necessary to ensure a replacement capable of withstanding 120 volts across the emitter-collector of the output and 4 kV across the input side to the output side.

You indicated that U2 is in a socket, do you know how to test U2 out of the circuit?

SAUL BRITTO · « **Reply #189 on:** February 18, 2016, 04:51:07 am »

rf+tech I measured some resistors of 1% 1M,100K,10K and the fluke is ok.

SAUL BRITTO · « **Reply #190 on:** February 18, 2016, 05:01:40 am »

This troubleshooting is better than fix the scope

. Yes I know how to test this LED.
Despite I have another CI of a HP1740A just don't know if it's the same.

SAUL BRITTO · « **Reply #191 on:** February 18, 2016, 05:10:59 am »

OOps the 1740A do not have this CI. Fail.

SAUL BRITTO · « **Reply #192 on:** February 18, 2016, 05:15:15 am »

I have a PS of a tektronix TDS320 tha has two CI Like this one,just don't know the electric feature.

SAUL BRITTO · « **Reply #193 on:** February 18, 2016, 06:11:30 am »

rf+tech how many volts I can use in this IC?i see -15V on the cathode,can I use +15 on the anode, on inverted situation? i jusT did put 0.6 V.Looks like it is with inttermitent work but,I am not sure.What is the right way to test that IC?

rf+tech · « **Reply #194 on:** February 18, 2016, 06:36:33 am »

Saul,

Quote

I have a PS of a tektronix TDS320 tha has two CI Like this one,just don't know the electric feature.

Use the IC part number and search for a datasheet and post the link here.

Quote

how many volts I can use in this IC?i see -15V on the cathode,can I use +15 on the anode, on inverted situation? i jusT did put 0.6 V.Looks like it is with inttermitent work but,I am not sure.What is the right way to test that IC?

Yes, inverted is okay, but the LED does not see 15 Volts in the circuit. The voltage is 15 - 11 = 4 Volts, with 270 Ohms in series. Measure the voltage drop across 270 Ohms, exactly as in the circuit.

A good test to show that Q4 is working correctly would be to carefully push the leads of red 20 mA LED into IC socket pins 1 and 2, with the proper polarity. The LED should turn on about 1.5 seconds after the scope is turned on. The actual current through R45 (270 Ohms) and the LED will be a function of Q4 gain and Q4 base current supplied by R44 (68 kOhms). Measure the voltage drop across R45 with the red LED for reference.

Continue tomorrow,

RF+ Tech

RF+ Tech

SAUL BRITTO · « **Reply #195 on:** February 18, 2016, 06:40:56 am »

I used breadboard

SAUL BRITTO · « **Reply #196 on:** February 18, 2016, 07:24:07 am »

re+tec here is the datasheet http://www.vishay.com/docs/83660/moc8101.pdf

SAUL BRITTO · « **Reply #197 on:** February 18, 2016, 07:54:48 am »

Well, I tested this IC of datasheet and now I have 2.45V across R45 and maybe a current of 9mA.

rf+tech · « **Reply #198 on:** February 18, 2016, 03:03:28 pm »

Quote

I tested this IC of datasheet and now I have 2.45V across R45 and maybe a current of 9mA.

Very good Saul, this is the kind data needed.

The MOC8101 minimum breakdown voltage (BVceo) is only 30 Volts. U2 is expected to withstand 100 Volts, the MOC8101 output may have already failed.

Please put original U2 on a breadboard with 270 Ohms in series and supply 4 Volts.
What is the voltage across 270 Ohms?

Good engineering decisions depend on good data, not guesses.

SAUL BRITTO · « **Reply #199 on:** February 18, 2016, 06:15:59 pm »

Look: contrary to logic I put MOC81 on the oscilloscope and got 2.7V acros R45 and -14 on pin 1 of U1 but the picture remains the same (Just for quick test).

SAUL BRITTO · « **Reply #200 on:** February 18, 2016, 07:14:19 pm »

Replacing that R45 270 Ohms that was 320 in fact, I can measure across it 2.60V and 9.6mA almost that 10mA
You said before.

But no with the original U2,ok?


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