Author Topic: Very nice HP1745A with little problems.  (Read 18516 times)

0 Members and 1 Guest are viewing this topic.

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #50 on: October 15, 2014, 10:16:29 am »
Arrrgh.... Duh and so on!!!
I have all kind of resistors.
I was sure about it I have 39.2k.
And what do you think?
Yeah, you won!!!!
I don't have.

Sometimes I would like to kill Mr. Murphy with my own naked hands.
I just wish they had strangled him in the cradle.
« Last Edit: October 15, 2014, 10:22:14 am by TGyuri »
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 11263
  • Country: us
  • DavidH
Re: Very nice HP1745A with little problems.
« Reply #51 on: October 15, 2014, 03:18:27 pm »
I think I have found it!
Resistor R7 39.2K seems to be an open circuit.
So signal just going thru C3 which is parallel with it.
I'm going to solder.  :)

R7 should definitely not show open.

Arrrgh.... Duh and so on!!!
I have all kind of resistors.
I was sure about it I have 39.2k.
And what do you think?
Yeah, you won!!!!
I don't have.

I do not think the value of R7 is that critical.  The closest standard value within 5% should at least work until you can get an exact replacement.

Quote
Sometimes I would like to kill Mr. Murphy with my own naked hands.
I just wish they had strangled him in the cradle.

If you tried that, something would just go wrong and Mr. Murphy would live.
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #52 on: October 15, 2014, 03:59:45 pm »
You are a good man, David!
I'm just puts together things.
So we can see the result soon.
Regards,
Gyuri
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #53 on: October 15, 2014, 06:56:30 pm »
So, that resistor was the guilty!
It works now, despite I didn't make any setting regarding R12/C11.
Only I settled them about middle position.
On the attached you can see output of Jim Williams generator with 5ns/DIV and 0.2V/DIV settings.
Its voltage peak seems low to me, so there will be some work yet, I think.
The more so as now it can't be done turn off the scale illumination.
If you remember how this thing started it is frustrating me and very funny indeed at the same time.
In this regard I'm the guilty for sure.
Main rule was violated, by myself, don't try to change more thing at once, if you are repair something.
So I have killed something around Q11 Q12 VR3 etc. on LVPS, while I implemented a socket and a heat sink for Q12.
Never mind.
I will repair it certainly, and now it is easy to change Q12, at least. :)

Dear David!

I now drinks a beer for your health!
Many thanks again!
continuation follows

Cheers!
https://hbpeza-ch3301.files.1drv.com/y2pqM36ild0SoAx9L65s2Zw2kVe1PWbfkv_JMa90kGqxU6RIcJoqbPzI-vMO02IwsUEh9qu4Q7ZOLHQsiwAaFNl3sldgo_8lCN3OYfXGT393kg/Img00820001_1.JPG?psid=1

Those confluent mottlings on photo are only reflections captured by camera.
(and some particles of dust)

Gyuri
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #54 on: October 15, 2014, 08:39:11 pm »
I'm at 26.5 ns now with some settings on R12/C11.
So it is now, as you said.
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 11263
  • Country: us
  • DavidH
Re: Very nice HP1745A with little problems.
« Reply #55 on: October 16, 2014, 11:23:53 am »
I'm at 26.5 ns now with some settings on R12/C11.
So it is now, as you said.

Adjust R12 and C11 for best shape and declare victory!

On my Tektronix oscilloscopes, the equivalent adjustments make a noticeable difference in both the shape of the leading edge and visually on the CRT but it is not like anything will fail if they are adjusted wrong.

On the attached you can see output of Jim Williams generator with 5ns/DIV and 0.2V/DIV settings.
Its voltage peak seems low to me, so there will be some work yet, I think.

If you use a charge line on the pulse generator instead of the collector capacitor, then the pulse will have a flat or at least flatter top which will allow the height to be seen even if the oscilloscope is too slow which is the case here.  It is much easier to use an edge with a flat top than a pulse to measure oscilloscope bandwidth.
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #56 on: October 16, 2014, 07:07:15 pm »
Best shape and fastest rise time are antagonists of each other.
So you say, I must concentrate for best shape with no ringing, even if degraded risetime?
I will setting it according this.
I have repaired (again) screen illumination.
I was killed that I-dont-know-what-a-type power transistor on A16 board.
I'm just curious, is there anybody who know what type transistor is?
I know it is a NPN power darlington with about 70W TDP.
I have chosen something, let it be say TIP 142.
It works again now.
Altough probably I will never using it.  :)

Regards,

Gyuri
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 11263
  • Country: us
  • DavidH
Re: Very nice HP1745A with little problems.
« Reply #57 on: October 17, 2014, 02:09:25 am »
Best shape and fastest rise time are antagonists of each other.
So you say, I must concentrate for best shape with no ringing, even if degraded risetime?
I will setting it according this.

It is true that you generally cannot have both at the same time but in this case, the rise time just has to be fast enough for unblanking to finish before the vertical signal reaches the CRT after traveling through the delay line.  The service manual says to adjust R12 and C11 for best shape.

Quote
I have repaired (again) screen illumination.
I was killed that I-dont-know-what-a-type power transistor on A16 board.
I'm just curious, is there anybody who know what type transistor is?
I know it is a NPN power darlington with about 70W TDP.
I have chosen something, let it be say TIP 142.
It works again now.
Altough probably I will never using it.  :)

I know there are indexes to convert HP part numbers to industry standard part numbers but I do not have one.  I would have to study the circuit and see the original transistor.
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #58 on: October 17, 2014, 06:42:29 am »
I know there are indexes to convert HP part numbers to industry standard part numbers but I do not have one.  I would have to study the circuit and see the original transistor.

It is not important, David.
It works excellently with TIP142 what I have choosed.
I only would like to know its type.
I have a HP parts number table, what I have found on net.
(I have attached it, thanks to Greg Davis who was the original uploader.)
But it doesn't helped.
I the SM its circuit number on A16 Service Sheet 3 is Q12, while in Replacable Parts list it is somehow confused, I suspect its number is Q14  HP P/N 1854-0553 or 0565
or something, not so readable, it is a TRANSISTOR NPN DAR. PO=70W FT=1MHz.
But it doesn't matter David, it is only an academic question.
I must have to lay back to bed now, with some ice.
(Without whiskey.)  ;)
« Last Edit: October 17, 2014, 06:56:03 am by TGyuri »
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #60 on: October 17, 2014, 07:19:00 am »
Yeah, and I have found a broken diode in this picture:
https://public.dm2301.livefilestore.com/y2p80Q22H6kCXXsfIP2rUYb2ENFlDDzDrnfz4mOGpnRjVkJAnL1gWcwoRlZxIgpF4OjwtaBjC4h95IsGqxp4cUyhPZrIdiwSOp9M2KDd27_MqY/Img00160001_1.JPG?psid=1
It is on the pic's left side, between that two spring steel sheet.
It is soldered on the pins of MAGx5 switch.
I'm don't know yet, what is it.
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #61 on: October 17, 2014, 10:17:06 am »
I think, I have found it:
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #62 on: October 17, 2014, 10:27:13 am »
And what does it do?
I suspect doing nothing, if we take into account the broken status..
Yes, I know it is a 2.37V zener.
But it causing what?
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #63 on: October 17, 2014, 12:05:33 pm »
My bad, again!
it is 5.1 V zener actually.
No, it is not.
« Last Edit: October 17, 2014, 12:43:43 pm by TGyuri »
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #64 on: October 17, 2014, 12:33:17 pm »
In this moment I really don't know. >:(
From that wrecked diode body, it is impossible to read its number.
But it was VR6 so it's a very special piece.
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 11263
  • Country: us
  • DavidH
Re: Very nice HP1745A with little problems.
« Reply #65 on: October 17, 2014, 01:01:00 pm »
The zener diode has something to do with the vertical positioning range and also controls the vertical shift used to align the traces when x5 vertical magnification is used.  A thorough checkout would have revealed a problem.

Quote
Something Motorola, I think.

It is definately a Motorola part but the number is an HP house number.  "House number" is the term I learned for OEMed parts with custom numbers.

Quote
It is not important, David.
It works excellently with TIP142 what I have choosed.
I only would like to know its type.
I have a HP parts number table, what I have found on net.
(I have attached it, thanks to Greg Davis who was the original uploader.)
But it doesn't helped.
I the SM its circuit number on A16 Service Sheet 3 is Q12, while in Replacable Parts list it is somehow confused, I suspect its number is Q14  HP P/N 1854-0553 or 0565
or something, not so readable, it is a TRANSISTOR NPN DAR. PO=70W FT=1MHz.

I found the same problems.  It is Q12 on the schematic but Q14 in the parts list and that is hard to read.  The part number shown in the photo is obviously wrong because the wrong part was used to replace it.

The number in the parts list might be 1854-0663 which is TIP140 making your TIP142 an ideal replacement.
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #66 on: October 17, 2014, 01:08:19 pm »
Well, it was VR6 actually, I think I will never get something similar like it was:

1902-3002 SZ10939-2 CD35526 DO7 2.37V 5% 400mW TC -0.074%

 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #67 on: October 17, 2014, 01:21:04 pm »
Thank you David,
It is good to me to know, that you are with me.

Yes, you absolutely right about Q12 part number, you have a good eye, I doesn't found it.
It is really that TIP140, so my more or less blind choice was absolutely good.
Well done, I like it!
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 11263
  • Country: us
  • DavidH
Re: Very nice HP1745A with little problems.
« Reply #68 on: October 17, 2014, 01:23:05 pm »
In this moment I really don't know. >:(
From that wrecked diode body, it is impossible to read its number.
But it was VR6 so it's a very special piece.

The schematic and parts list say it is a 2.37 volt zener diode in a DO-7 (glass) package which is what your photo shows.  The DO-7 package means that its power rating is about 500 milliwatts.

A 2.4 volt zener diode like a 1N5221, BZX55B2V4, or ZX2V4A should work fine in its place.  Even 4 silicon diodes in series would work as a 2.4 volt diode.
 

Online PA0PBZ

  • Super Contributor
  • ***
  • Posts: 4346
  • Country: nl
Re: Very nice HP1745A with little problems.
« Reply #69 on: October 17, 2014, 01:29:11 pm »
Well, it was VR6 actually, I think I will never get something similar like it was

http://www.mival.ro/diode-znr-2-37v-1902-3002-18-en
Keyboard error: Press F1 to continue.
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #70 on: October 17, 2014, 01:47:39 pm »
Thanks for the reply guys!
That mival link is sensational, it is here in the neighborhood, I will contact to them!  :)
Till then will be four diodes.
But it will be perfect if I can get original part.
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 11263
  • Country: us
  • DavidH
Re: Very nice HP1745A with little problems.
« Reply #71 on: October 17, 2014, 02:08:33 pm »
Thanks for the reply guys!
That mival link is sensational, it is here in the neighborhood, I will contact to them!  :)
Till then will be four diodes.
But it will be perfect if I can get original part.

Remember to reverse the 4 diodes.  The zener diode operates in reverse breakdown to generate 2.4 volts but 4 silicon diodes in series will need to be forward biased to do the same job.

The 4 diodes in series will be less accurate and drift with temperature more but the oscilloscope should work fine.
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #72 on: October 17, 2014, 05:38:01 pm »
Thanks for your clarification, David!
Maybe I have recognised it from myself, maybe not.
It can't be know, because I'm Wacky.
For example, I realized TIP142 has reverse pin order compared to that don't-know-what-is-it-darlington.
I have used only my brain! :)
BTW, I have got some 2,4V zeners.
So I have looked at once again that little part of SS4.
I have surprised in some extent, because I have recognised that simple fact:
At MAGx5 there is nothing to do with that precious 2.37V zener with special thermal coefficients.
Because in this setting it is shunted by MAGx5 switch!
May be it is only news for me.  :)
It is certainly has there because of eliminate trace shifting.
I have observed some annoying trace shift on scope, soon as I have got it.
But I have thought, if it will be in a good shape, I will carry out some calibration, and it will be gone.
I have soldered a 2.4V zener to its place.
It certainly has some effect on trace shift.
But I haven't satisfied.
I have got about 2V through it in normal position.
And in the light of the exploring above, there is exactly 0V on it. (With MAGx5 pushed.)

It needs further examining.

I think, I drink now some further beers for health of David and myself and everbody else, and I will let it down a bit.
Now, I listen some music rather.
Happy weekend for all of us!
Kind regards,
Gyuri
« Last Edit: October 17, 2014, 05:48:14 pm by TGyuri »
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Some troubled thoughts.
« Reply #73 on: October 17, 2014, 07:33:58 pm »
As I getting more and more beer, I'm in a more and more in a philosophical mood.
I think, it is not news, most of us are a similar way.
I'm wondering, why David dealing with me?
Apart of that he is a very nice man, as I know him better and better.
(I think, at least.)
There are important things in the world.
One of them, the most important according to me, the knowledge.
(I don't know may be arts are more important, I'm hang in the balance, as always.)
And what about money and power, you may ask it?
My answer is, even a completely idiot can have money and power, while lacking any knowledge.
It is the worst and most hazardous combination I think.
These people worth nothing in my eyes, maybe double zero.
They even can share out all of the money they have.
They will be absolute nothing.
Nobody will remember of them.
BTW, you can not take money to the afterlife.
But what about knowledge?
If you have much knowledge, and you share it, you will have increasingly more and more knowledge hereby.
BTW, you can not take knowledge to the afterlife.
So if you share it, it will be remain with us, and you will be worth more and more.
And posterity will be grateful to you.
I know, all of above about me.
Perhaps not only about myself, I hope.
I don't know, people like Jim Williams, Nelson Pass, David William Hess etc., when dealing with people like me, Wacky Gyuri thinks things like above?
I do not think so, and that's the beauty of it.
Excuse me, if I seems to be muddling, please take account my crappy english.
And those beers also.

Kind regards,

Wacky Gyuri
« Last Edit: October 17, 2014, 07:35:32 pm by TGyuri »
 

Offline TGyuri

  • Regular Contributor
  • *
  • Posts: 57
  • Country: 00
Re: Very nice HP1745A with little problems.
« Reply #74 on: October 17, 2014, 08:02:37 pm »
I think I have got it!
What do you think, David?

Sorry for blurred picture.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf