Author Topic: Tektronix 7633 Scope, Can anyone please help Old64goat!!!  (Read 31133 times)

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Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #25 on: May 03, 2017, 12:59:06 am »
Can someone please provide screen shots or pdf scans of what the old64goat is asking for?

The link casinada gave is the scan I use for the 7633 and has all of the schematics toward the back.  They are even in color; Tektronix liked to use blue ink.

http://exodus.poly.edu/~kurt/manuals/manuals/Tektronix/TEK%207633%20%20Service.pdf

Quote
"Where is schematic 7?

PDF page 296.

Quote
I can't find schematic 8, ALL fuses test good.

PDF page 300.

Quote
What may help is a print out of all the schematics & voltage test points for this no HV problem.

I usually end up printing out selected schematics on 11x17 paper when working on a problem like this.
 
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Offline Electro Detective

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #26 on: May 03, 2017, 02:06:44 am »
I learn something every time I watch an Old64goat video, be it his tech tips or flap.  :-+

He checked the heat/age failed glue ends 0.15 amp glass fuse with a meter and got 20 ohms reading = not good

I 'may' have missed that with a hurried visual or simple buzz/fast continuity check, especially if I can't pull a fuse out to read values and do a physical inspection.

----------------------
 :popcorn:    F W I W:   :popcorn:

If it was me checking that 'please help   :'( I'm sick of auctions and want to work again'  Tek 7633, I would first do a basic visual on the unit, the front panel plugin connectors and lube them,
then do a turn on, turn up the Intensity, then start working ALL those buttons and knobs at random and in multiples, and see if anything appears briefly on the screen.

Working the lot BEFORE applying power first is recommended, especially the power switch and it's banged up dials etc, and then with power applied.

Better still, have a mounted video camera or phone running to see on replay what buttons and knob combo caused a brief flicker, trace, spot or no show etc

If no go, try removing and repositioning plugins, in any basic combo possible so the unit will function, till something appears or not.


If still no life, roll up the shirt sleeves and give the unit a peaved 'Clint squint'   >:(

Warm the entire unit up with a portable fan heater and / or use a hairdryer for tight spots, especially if in a cold location and try ALL the above again.


No good? Tip the unit on it's side and upside down (carefully) warm/heat up and try again in those positions.   


FYI to gigglers  :-DD  I fixed a few same vintage 'for parts or not working' 5000 and 4xx series Teks and Phillips exactly this way years ago, and after lubing up any offender dry sticky switches, knobs and connectors, and elbow grease, they worked perfectly and within spec   ..without even turning on the multimeter and untangling the leads.
 
If anything, the time spent/wasted? above (one hour at most) will at least confirm that the unit has issues that need thorough service manual based investigative diagnosis, which as you guessed by now, I prefer to AVOID like the plague if I can, lol   

and if you can't fix it or afford repairs, the next swap meet or Ebay will gladly sort it out for you, and get that valuable bench real estate  vacant again    8)

 
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #27 on: May 03, 2017, 02:58:32 am »
David,
Bill is having trouble reading his copy of the manual. This is what he just wrote me:
"I NEED a service manual I can read, I can't even read the the schematic part numbers and I can't find the HV board in the PDF.
I can NOT find schematic 7,  I can NOT find schematic 8, I hate this PDF, I have 4 of them and they are all no good, they are so bad I can't even read the parts numbers, voltages, etc..
Where is Q1195 on the HV board?
Where is C1198 on the Z-AXIS board?
What I need is for someone to take a clear photo of these parts OR a Tektronix 7633 service manual from Teltronix in PAPER form..
If I can't get a manual that I can't read I will give up."

Any ideas?

Thank you for helping!!!
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #28 on: May 03, 2017, 03:04:26 am »
I learn something every time I watch an Old64goat video, be it his tech tips or flap.  :-+

He checked the heat/age failed glue ends 0.15 amp glass fuse with a meter and got 20 ohms reading = not good

I 'may' have missed that with a hurried visual or simple buzz/fast continuity check, especially if I can't pull a fuse out to read values and do a physical inspection.

----------------------
 :popcorn:    F W I W:   :popcorn:

If it was me checking that 'please help   :'( I'm sick of auctions and want to work again'  Tek 7633, I would first do a basic visual on the unit, the front panel plugin connectors and lube them,
then do a turn on, turn up the Intensity, then start working ALL those buttons and knobs at random and in multiples, and see if anything appears briefly on the screen.

Working the lot BEFORE applying power first is recommended, especially the power switch and it's banged up dials etc, and then with power applied.

Better still, have a mounted video camera or phone running to see on replay what buttons and knob combo caused a brief flicker, trace, spot or no show etc

If no go, try removing and repositioning plugins, in any basic combo possible so the unit will function, till something appears or not.


If still no life, roll up the shirt sleeves and give the unit a peaved 'Clint squint'   >:(

Warm the entire unit up with a portable fan heater and / or use a hairdryer for tight spots, especially if in a cold location and try ALL the above again.


No good? Tip the unit on it's side and upside down (carefully) warm/heat up and try again in those positions.   


FYI to gigglers  :-DD  I fixed a few same vintage 'for parts or not working' 5000 and 4xx series Teks and Phillips exactly this way years ago, and after lubing up any offender dry sticky switches, knobs and connectors, and elbow grease, they worked perfectly and within spec   ..without even turning on the multimeter and untangling the leads.
 
If anything, the time spent/wasted? above (one hour at most) will at least confirm that the unit has issues that need thorough service manual based investigative diagnosis, which as you guessed by now, I prefer to AVOID like the plague if I can, lol   

and if you can't fix it or afford repairs, the next swap meet or Ebay will gladly sort it out for you, and get that valuable bench real estate  vacant again    8)

Thank you for all that detailed help!!!
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #29 on: May 03, 2017, 03:06:51 am »
Can someone please provide screen shots or pdf scans of what the old64goat is asking for?

The link casinada gave is the scan I use for the 7633 and has all of the schematics toward the back.  They are even in color; Tektronix liked to use blue ink.

http://exodus.poly.edu/~kurt/manuals/manuals/Tektronix/TEK%207633%20%20Service.pdf

Quote
"Where is schematic 7?

PDF page 296.

Quote
I can't find schematic 8, ALL fuses test good.

PDF page 300.

Quote
What may help is a print out of all the schematics & voltage test points for this no HV problem.

I usually end up printing out selected schematics on 11x17 paper when working on a problem like this.

Thank you David for telling him what pages to print!!!
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #30 on: May 03, 2017, 05:48:39 pm »
Hello,
Old64goat just sent this message:

"As I said I can not find Q1195.
I can not find C1198.
The way that PDF is set uo I have to scroll through all 320 pages to try to find anything, I hate it."

Does anyone know what page Q115 & C118 are located on?

Thank you for helping!!!
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #31 on: May 03, 2017, 06:03:24 pm »
I just got another update from Old4goat:
"This is getting OLD...LOL
I did find Q1185 & C1198 on the HV schematic which I did PRINT OUT, but when I look at the HV board "picture" they are NOT shown.
I spent two hours looking at the pictorials & schematics and printed them all out.
If Q1195 & C1198 are INSIDE the HV box they must be hidden and are not serviceable.
Another thing is how the heck am I going to see if I got +15 volts across C1198 if it is INSIDE the HV box?"

Can someone please advice on next steps to take?

Thank you for helping!!!
 

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #32 on: May 03, 2017, 06:23:00 pm »
I just got another update from Old4goat:
"This is getting OLD...LOL
I did find Q1185 & C1198 on the HV schematic which I did PRINT OUT, but when I look at the HV board "picture" they are NOT shown.
I spent two hours looking at the pictorials & schematics and printed them all out.
If Q1195 & C1198 are INSIDE the HV box they must be hidden and are not serviceable.
Another thing is how the heck am I going to see if I got +15 volts across C1198 if it is INSIDE the HV box?"

Can someone please advice on next steps to take?

Thank you for helping!!!

This is getting to be hard work with Old4goat. I suspect the transistor he seeks is the main switcher for the HV SMPS, they are normally a TO-220 or similar and bolted to the frame or some heatsink. When this is the case it is often identified in the schematic with a dotted line indicating the device is NOT on the PCB.

Service manuals are written for technicians and without knowledge of the conventions used some considerable time studying and comparing with the physical layout MUST be invested for it all to make sense.
There are NO shortcuts, he must spend the time to understand the schematics, principles of operation, physical layout and reasons for it all.
All we that are self taught have had to follow this path and it need be seen as an investment of time for your future.
Good luck.
Avid Rabid Hobbyist.
Some stuff seen @ Siglent HQ cannot be shared.
 
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Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #33 on: May 03, 2017, 06:48:43 pm »
Hello,
Old64goat just sent this message:

"As I said I can not find Q1195.
I can not find C1198.
The way that PDF is set uo I have to scroll through all 320 pages to try to find anything, I hate it."

Does anyone know what page Q115 & C118 are located on?

All of the high voltage inverter circuit including C1198 which decouples the unregulated +15 volt supply to the high voltage inverter and Q1195 which is the TO-3 power transistor for the inverter is shown in the upper left corner of schematic 7 which is PDF page 296.

The fuse for the unregulated +15 volt supply going to the high voltage inverter is shown on the left side of schematic 8 which is PDF page 300.

The 7633 is one of the increasingly few Tektronix oscilloscopes which I have *not* made a compilation of schematics for because the existing freely available service manual scan is pretty good.  I have actually done about half of the work to make a set of dedicated schematics for the 7633 so maybe I should complete that.  Do not count on anything quickly though as this takes time and the scans would not really look any better than the existing service manual.

Q1195 itself is a TO-3 packaged transistor and is exposed where it is mounted to the aluminum cover over the high voltage board.  Look under the high voltage test point toward the back of the oscilloscope.  (1) The case is the collector so it can be probed with a voltmeter to see if the +15 volt unregulated supply to the inverter is present.  Be careful of course not to short it out to the chassis because this will blow fuse F814.  When the inverter is operating, the exposed collector of Q1195 is where the primary side oscillating waveform of roughly 40kHz can be measured.

Usually the failure in this circuit is Q1195 drawing too much current because of some other failure which blows fuse F814.  For this reason if the fuse is blown or if Q1195 is bad, the cover should be removed to gain access to the high voltage circuit board and the parts in the high voltage inverter should be tested.  I am not sure how to get the cover off.

Sometimes Q1195 is blown and if that is the case, then it can be replaced with a modern On Semiconductor 2N3771G or 2N3772G.  The original 2N3055 is a 0.3 MHz part so modern 2N3055s with their 2.0MHz and higher Ft tend to spuriously oscillate but an old 2N3055 could work.

For testing purposes, I would remove fuse F814 and use a current limited power supply to power the high voltage inverter through the fuse connection.  Alternatively an LM317 configured as a current source with a single 2 watt 1.0 ohm resistor could replace the fuse temporarily.

(1) PDF pages 316 and 318 show the location of Q1195 as part number 110 toward the center top of the drawings but I agree with Old4goat, these drawings are difficult to read.
« Last Edit: May 03, 2017, 09:17:02 pm by David Hess »
 

Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #34 on: May 03, 2017, 07:07:09 pm »
This is getting to be hard work with Old4goat. I suspect the transistor he seeks is the main switcher for the HV SMPS, they are normally a TO-220 or similar and bolted to the frame or some heatsink. When this is the case it is often identified in the schematic with a dotted line indicating the device is NOT on the PCB.

In this case it is an old slow 0.3MHz 2N3055 operating in a power blocking oscillator.  The case (collector) is exposed and visible below the high voltage test point.  Earlier oscilloscopes in this series used a push-pull configuration with two 2N3055s and I do not know why Tektronix changed it, maybe the single transistor version was less expensive?
 
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #35 on: May 03, 2017, 07:53:23 pm »
I just got another update from Old4goat:
"This is getting OLD...LOL
I did find Q1185 & C1198 on the HV schematic which I did PRINT OUT, but when I look at the HV board "picture" they are NOT shown.
I spent two hours looking at the pictorials & schematics and printed them all out.
If Q1195 & C1198 are INSIDE the HV box they must be hidden and are not serviceable.
Another thing is how the heck am I going to see if I got +15 volts across C1198 if it is INSIDE the HV box?"

Can someone please advice on next steps to take?

Thank you for helping!!!

This is getting to be hard work with Old4goat. I suspect the transistor he seeks is the main switcher for the HV SMPS, they are normally a TO-220 or similar and bolted to the frame or some heatsink. When this is the case it is often identified in the schematic with a dotted line indicating the device is NOT on the PCB.

Service manuals are written for technicians and without knowledge of the conventions used some considerable time studying and comparing with the physical layout MUST be invested for it all to make sense.
There are NO shortcuts, he must spend the time to understand the schematics, principles of operation, physical layout and reasons for it all.
All we that are self taught have had to follow this path and it need be seen as an investment of time for your future.
Good luck.
Good advice, thank you for sharing!!!
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #36 on: May 03, 2017, 09:14:52 pm »
Here is an update from the Old64goat:
"First here is a quote from David Hess:
"All of the high voltage inverter circuit including C1198 which decouples the unregulated +15 volt supply to the high voltage inverter and Q1195 which is the TO-3 power transistor for the inverter is shown in the upper left corner of schematic 7 which is PDF page 296.

The fuse for the unregulated +15 volt supply going to the high voltage inverter is shown on the left side of schematic 8 which is PDF page 300."
========================================================
On ALL my PDF manuals of which I have 4, all the same 320 page PDF files, there are no schematics on pages 296 or 300, so I had to search for them by scrolling through many pages.
With that said I found Q1195, THANKS David!
I measured the voltage on the collector, it reads +22.3 volts, I know David said +15 volts unregulated

So could that be normal as it is not regulated?

I do have some very old 2N3055 power transistors but I would hate to pull out the HV board and have it blow.

BTW I no longer have a transistor tester, years ago I had a Sencore Super Cricket but that got sold dirt cheap.

From what David said fuse F814 supply's the unregulated +15 volts to Q1195, but like I mentioned in this posting PDF Page 300 does not show a schematic, in fact there are NO schematic numbers shown in these PDF manuals I have but it does show what circuit they are.

This is one big reason I am having such a bad time with these PDF's
THANKS guys"

David, if you have time what do you think? 

Thank you for helping solve this problem!!!
 

Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #37 on: May 03, 2017, 09:38:01 pm »
I measured the voltage on the collector, it reads +22.3 volts, I know David said +15 volts unregulated

So could that be normal as it is not regulated?

That is the normal voltage.  The +15 volt unregulated supply is used to feed the +15 volt regulator and it also feeds the high voltage inverter.  Its minimum voltage has to be higher than the dropout voltage of the +15 volt regulator so +22.3 volts is about right.

Quote
From what David said fuse F814 supply's the unregulated +15 volts to Q1195, but like I mentioned in this posting PDF Page 300 does not show a schematic, in fact there are NO schematic numbers shown in these PDF manuals I have but it does show what circuit they are.

Our PDF files might have a different number of pages.

The schematic numbers are marked in a lower corner with the schematic number.

Artek Manuals has a complete scan of the 7633 manual and they includes indexes making it easy to find specific pages for about $7.  Their quality is usually pretty good.

http://artekmanuals.com/manuals/tektronix-manuals/

Quote
David, if you have time what do you think? 

If the inverter is operating, then there should be a high level of AC at the collector of the transistor so look for that using an AC voltmeter or another oscilloscope.

I think the only way the inverter could not be oscillating *and* fuse F814 not be blown is if Q1195 was open or if the transformer bias winding to the base of Q1195 was open.  If Q1195 and the transformer was good, then the high voltage regulator circuit would drive Q1195 hard blowing fuse F814 and that did not happen.

So the likely problem is Q1195 being open.  Unfortunately this leaves the question of why which is why I recommend gaining access to the high voltage board to test the transistors in the regulator circuit and measure the resistance of the transformer primary and bias winding.

Before taking anything apart, check for an AC voltage on the collector of Q1195.  It should be about 40kHz.
 
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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #38 on: May 03, 2017, 09:44:40 pm »
A quick test to see if these inverters are working is to look for the EMI they produce when running. David has mentioned 40 KHz and this can be identified with another scope without connecting but just using a probe close by, ahla near field probe style.
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #39 on: May 03, 2017, 10:33:25 pm »
I measured the voltage on the collector, it reads +22.3 volts, I know David said +15 volts unregulated

So could that be normal as it is not regulated?

That is the normal voltage.  The +15 volt unregulated supply is used to feed the +15 volt regulator and it also feeds the high voltage inverter.  Its minimum voltage has to be higher than the dropout voltage of the +15 volt regulator so +22.3 volts is about right.

Quote
From what David said fuse F814 supply's the unregulated +15 volts to Q1195, but like I mentioned in this posting PDF Page 300 does not show a schematic, in fact there are NO schematic numbers shown in these PDF manuals I have but it does show what circuit they are.

Our PDF files might have a different number of pages.

The schematic numbers are marked in a lower corner with the schematic number.

Artek Manuals has a complete scan of the 7633 manual and they includes indexes making it easy to find specific pages for about $7.  Their quality is usually pretty good.

http://artekmanuals.com/manuals/tektronix-manuals/

Quote
David, if you have time what do you think? 

If the inverter is operating, then there should be a high level of AC at the collector of the transistor so look for that using an AC voltmeter or another oscilloscope.

I think the only way the inverter could not be oscillating *and* fuse F814 not be blown is if Q1195 was open or if the transformer bias winding to the base of Q1195 was open.  If Q1195 and the transformer was good, then the high voltage regulator circuit would drive Q1195 hard blowing fuse F814 and that did not happen.

So the likely problem is Q1195 being open.  Unfortunately this leaves the question of why which is why I recommend gaining access to the high voltage board to test the transistors in the regulator circuit and measure the resistance of the transformer primary and bias winding.

Before taking anything apart, check for an AC voltage on the collector of Q1195.  It should be about 40kHz.

David, thank you for all the details!!!
 

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #40 on: May 03, 2017, 10:35:16 pm »
A quick test to see if these inverters are working is to look for the EMI they produce when running. David has mentioned 40 KHz and this can be identified with another scope without connecting but just using a probe close by, ahla near field probe style.

tautech, thank you for this information, Bill does have another scope to use to check it.

Thank you for helping!!!
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #41 on: May 03, 2017, 11:20:00 pm »
Here is another update from Bill:
"MORE INFORMATION:
I removed the fuse  F814 and inserted +15 volts, I did this on the end of the fuse holder that goes to the HV supply.

My power supply showed about 500ma draw at +15 volts.

Then I took my scope and I saw a nice clean sine wave but I could not read the frequency.

I then connected my frequency counter using my scope probe set on the RX1 setting because I could not get any reading on the RX 10 setting, it read 41KC

NOW hear is the "kicker", I replaced F814 and of course I got the +22.3 volts on the collector, the frequency counter was around 12KC and it fluctuated around that frequency.

Very strange it seemed to give me 41KC at +15 volts but not with +22.3 volts.

The AC on the collector is low voltage, I had to set my scope to almost the max sensitvity so that is why I set my scope probe to X1."

Any ideas on this new information?

 Thank you for helping out solving this problem!!!
 

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #42 on: May 03, 2017, 11:50:42 pm »
It appears Old64goat may be in the Tektronix tech trap merry go round I mentioned earlier,
working through test points and voltages whilst being hampered by dicky intermittent contact switches, dials, connectors,
all working together and at random to prevent triggering and displays on the screen, and come and go not HV readings, and so forth.  :-//

Assuming of course no half @ssed repairs were performed on this 7633, on a previous owner/s troubleshoot rodeo ride.

Too bad I haven't got that 7633 in front of me   :-BROKE

Mr. Carlsons Lab time, would make an awesome tear down and repair video!   :popcorn:   :popcorn:   :popcorn:

 

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #43 on: May 03, 2017, 11:53:26 pm »
Can anyone confirm whether the HV is directly generated or has a cockroft-walton multiplier? I ask because I've worked on HeNe laser power supplies where the capacitors in the multiplier looked fine at lower voltages but would arc internally at full voltage and short. It might be worth measuring the HT connection while ramping up the HV circuit on a variable bench supply and see if you get any HV up to a certain input voltage.
 
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Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #44 on: May 04, 2017, 12:22:44 am »
So with a higher supply voltage, the frequency was lower and the AC signal was smaller?  Here is what I think:

1. Aluminum electrolytic capacitor C1198 is worn out.  At higher frequencies, the reactance of L1198 will be higher so the AC voltage seen at the collector of Q1195 will be higher.  The high voltage inverter will not operate if decoupling capacitor C1198 is worn out.

2. Usually the control loop will drive Q1195 hard if the output voltage (-1475) is low blowing fuse F814.  In this case, I suspect the fuse was replaced later if it was blown and driver Q1190 transistor was damaged or the gradual degradation of C1198 allowed excess drive current to damage driver Q1190.  In that case, Q1187 could supply enough current through the 1k resistor and Q1190's shorted emitter-base junction to raise the current through output transistor Q1195 to the level you measured but not high enough to blow fuse F814 again.

3. There is no voltage on the output because of the low impedance of the heater winding, the high impedance of L1198 when C1198 is bad, and low drive current from Q1190.

4. Possibly there is a short on the output side like at the high voltage multiplier but that cannot be the only problem.  If the problem was only on the secondary side, then fuse F814 would blow.

The above is somewhere to start anyway but access to the high voltage board will be necessary to replace C1198 and test driver Q1190.  I would just replace C1198 and test the old capacitor.  You said that you lack a transistor tester but do you have an LCR meter or impedance bridge for testing capacitors?  Just measuring the capacitance should be sufficient.
 
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #45 on: May 04, 2017, 12:31:05 am »
Can anyone confirm whether the HV is directly generated or has a cockroft-walton multiplier? I ask because I've worked on HeNe laser power supplies where the capacitors in the multiplier looked fine at lower voltages but would arc internally at full voltage and short. It might be worth measuring the HT connection while ramping up the HV circuit on a variable bench supply and see if you get any HV up to a certain input voltage.

Thank you for helping out!!!
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #46 on: May 04, 2017, 12:32:44 am »
So with a higher supply voltage, the frequency was lower and the AC signal was smaller?  Here is what I think:

1. Aluminum electrolytic capacitor C1198 is worn out.  At higher frequencies, the reactance of L1198 will be higher so the AC voltage seen at the collector of Q1195 will be higher.  The high voltage inverter will not operate if decoupling capacitor C1198 is worn out.

2. Usually the control loop will drive Q1195 hard if the output voltage (-1475) is low blowing fuse F814.  In this case, I suspect the fuse was replaced later if it was blown and driver Q1190 transistor was damaged or the gradual degradation of C1198 allowed excess drive current to damage driver Q1190.  In that case, Q1187 could supply enough current through the 1k resistor and Q1190's shorted emitter-base junction to raise the current through output transistor Q1195 to the level you measured but not high enough to blow fuse F814 again.

3. There is no voltage on the output because of the low impedance of the heater winding, the high impedance of L1198 when C1198 is bad, and low drive current from Q1190.

4. Possibly there is a short on the output side like at the high voltage multiplier but that cannot be the only problem.  If the problem was only on the secondary side, then fuse F814 would blow.

The above is somewhere to start anyway but access to the high voltage board will be necessary to replace C1198 and test driver Q1190.  I would just replace C1198 and test the old capacitor.  You said that you lack a transistor tester but do you have an LCR meter or impedance bridge for testing capacitors?  Just measuring the capacitance should be sufficient.

David, thank you for this valuable information and sharing your wisdom with us!!!
 

Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #47 on: May 04, 2017, 02:26:09 am »
Can anyone confirm whether the HV is directly generated or has a cockroft-walton multiplier? I ask because I've worked on HeNe laser power supplies where the capacitors in the multiplier looked fine at lower voltages but would arc internally at full voltage and short. It might be worth measuring the HT connection while ramping up the HV circuit on a variable bench supply and see if you get any HV up to a certain input voltage.

-1475 volts for the cathode is generated by a half wave rectifier (CR1215) which has a relay which cleverly converts it into a half wave voltage doubler (CR1215 and CR1210) to produce -3000 volts for reduced scan mode.

The +7000 volt PDA (post deflection acceleration) is produced by a half wave voltage doubler (one stage of a Cockcroft–Walton multiplier, CR1202 and CR1205) from a higher voltage extended winding on the transformer.

It is difficult to control the output because there is closed loop feedback from the -1475 or -3000 volt cathode supply which controls the inverter drive.  Just messing with the power to the primary side of the inverter will not control the output well and can damage the oscillator do to excessive current and heat if the input voltage is low.

The 7623A is a 7633 without reduced scan mode.  The 7623B is effectively a renamed 7633 and replaced both.
 
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #48 on: May 04, 2017, 11:33:02 am »
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #49 on: May 04, 2017, 08:06:25 pm »
David,
Bill just sent me this message for you:
"old64goat
I am printing all this information out, David has been a great help to me, please thank him for me!"
 


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