So my trusty scope is acting up.

At normal and low intensity, there is a chopped appearance to
the trace at a few hundred Hz. It's variable and at times,
increasing intensity also causes change in focus, and/or the
intensity doesn't go as high as it should.

I assume a problem in the HV.

Thanks for any info.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Sam Goldwasser wrote:
So my trusty scope is acting up.

At normal and low intensity, there is a chopped appearance to
the trace at a few hundred Hz. It's variable and at times,
increasing intensity also causes change in focus, and/or the
intensity doesn't go as high as it should.

I assume a problem in the HV.

Thanks for any info.


Maybe check the LV first. The bridges on this scope tend to go
half-bad, turning the bridges into half-wave rectifiers. Also the
filter caps can lose capacitance. Put the scope on a variac, turn the
variac down to 100 volts and put a scope on the PS test points. If you
see 60 Hz ripple, then it's the diodes, if it's 120Hz ripple, its the
capacitors.

The HV power supply has like a voltage quadrupler. Maybe a diode or
two has shorted there?

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.

"Ancient_Hacker" wrote in
ups.com:


Sam Goldwasser wrote:
So my trusty scope is acting up.

At normal and low intensity, there is a chopped appearance to
the trace at a few hundred Hz. It's variable and at times,
increasing intensity also causes change in focus, and/or the
intensity doesn't go as high as it should.

I assume a problem in the HV.

Thanks for any info.


Maybe check the LV first.

I agree;first,assume low voltage power supply problems.
EVERYTHING works off them.

(Sam,you oughta know this!)


The bridges on this scope tend to go
half-bad, turning the bridges into half-wave rectifiers. Also the
filter caps can lose capacitance. Put the scope on a variac, turn the
variac down to 100 volts and put a scope on the PS test points. If you
see 60 Hz ripple, then it's the diodes, if it's 120Hz ripple, its the
capacitors.

The HV power supply has like a voltage quadrupler. Maybe a diode or
two has shorted there?

Not likely,as reduced anode HV would result in a much dimmer and enlarged
displayed signal(in both dimensions),and the cal would be greatly affected.
Also,I don't think the HV would continue running with a shorted diode in
the multiplier. I believe the HV fuse would blow first.

BTW,at some point,increasing intensity will definitely affect focus.
The CRT cathode emits from a larger area,and gets worse as the CRT ages.

--
Jim Yanik
jyanik
at
kua.net

"Ancient_Hacker" wrote in
oups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either one
can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity modulation.

--
Jim Yanik
jyanik
at
kua.net

Jim Yanik writes:

"Ancient_Hacker" wrote in
oups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either one
can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity modulation.

Followup: The frequency of the chopped line does NOT correlate with
line frequency.

And I should note that at low intensity, it is worst going full off. With
the intensity turned up, it's not visible. There is minimal
if any geometric distortion of the trace (outside of the focus problem,
which doesn't always appear) so I doubt any LV power supplies
are involved that also feed the amps.

It's almost as if the Z input has some oscillation on it. When I first
noticed, I thought maybe the chopped blanking was misbehaving, but this
occurs on all vertical modes.

It's also related to warmup. At power-on, there is no problem. It takes
a of couple minutes to show up. The fan is running.

And even then, the severity varies randomly.

So, what could affect the Z modulation AND sometimes focus, but not geometry?

If it was the HV divider I guess a parts unit is the only source for a
replacement?

Thanks.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
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Sam Goldwasser wrote in message
...
So my trusty scope is acting up.

At normal and low intensity, there is a chopped appearance to
the trace at a few hundred Hz. It's variable and at times,
increasing intensity also causes change in focus, and/or the
intensity doesn't go as high as it should.

I assume a problem in the HV.

Thanks for any info.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above
is
ignored unless my full name AND either lasers or electronics is included
in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

I only have the manual for the 465 , not B variant.
But assuming ps similar I would suggest a problem leading to ripple on the
unreg 120V supply rail (bridge, caps )feeding the EHT oscillator/driver
circuitry or problem in that oscillator circuitry or of course, wallectomy
time, problem in the EHT step-up transformer


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Sam Goldwasser wrote in
:

Jim Yanik writes:

"Ancient_Hacker" wrote in
oups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either
one can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity
modulation.

Followup: The frequency of the chopped line does NOT correlate with
line frequency.

Perhaps HV oscillator freq?

And I should note that at low intensity, it is worst going full off.
With the intensity turned up, it's not visible. There is minimal
if any geometric distortion of the trace (outside of the focus
problem, which doesn't always appear) so I doubt any LV power supplies
are involved that also feed the amps.

Then you're down to decoupling caps.

It's almost as if the Z input has some oscillation on it. When I
first noticed, I thought maybe the chopped blanking was misbehaving,
but this occurs on all vertical modes.

A thought occurs to me;there's a 1uf/150V(IIRC) electrolytic on the wiper
of the CRT grid bias pot,to ground;that could be going bad.

It's also related to warmup. At power-on, there is no problem. It
takes a of couple minutes to show up. The fan is running.

And even then, the severity varies randomly.

So, what could affect the Z modulation AND sometimes focus, but not
geometry?

If it was the HV divider I guess a parts unit is the only source for a
replacement?

Yes,it was a TEK-made part,from their defunct hybrid/ICO in-house plant.
Removing a good one from a motherboard without damaging it is not an easy
task

--
Jim Yanik
jyanik
at
kua.net

Jim Yanik writes:

Sam Goldwasser wrote in
:

Jim Yanik writes:

"Ancient_Hacker" wrote in
oups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either
one can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity
modulation.

Followup: The frequency of the chopped line does NOT correlate with
line frequency.

Perhaps HV oscillator freq?

I don't think so. It's order of a few hundred Hz and not constant.

And I should note that at low intensity, it is worst going full off.
With the intensity turned up, it's not visible. There is minimal
if any geometric distortion of the trace (outside of the focus
problem, which doesn't always appear) so I doubt any LV power supplies
are involved that also feed the amps.

Then you're down to decoupling caps.

It's almost as if the Z input has some oscillation on it. When I
first noticed, I thought maybe the chopped blanking was misbehaving,
but this occurs on all vertical modes.

A thought occurs to me;there's a 1uf/150V(IIRC) electrolytic on the wiper
of the CRT grid bias pot,to ground;that could be going bad.

I'll check that.

It's also related to warmup. At power-on, there is no problem. It
takes a of couple minutes to show up. The fan is running.

And even then, the severity varies randomly.

So, what could affect the Z modulation AND sometimes focus, but not
geometry?

If it was the HV divider I guess a parts unit is the only source for a
replacement?

Yes,it was a TEK-made part,from their defunct hybrid/ICO in-house plant.
Removing a good one from a motherboard without damaging it is not an easy
task

Now it really doesn't like even normal intensity.

But the geometry (beam stiffness, etc.) is not affected. So, I'm
leaning toward a problem in the grid circuit, not the HV itself.

Does anyone know of a free source for decent quality schematics? I have
several complete manuals downloaded from various places but the resolution
of the schematics tends to be terrible and only marginally useful.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

On 18 Mar 2006 12:40:11 -0500, Sam Goldwasser
wrote:

Jim Yanik writes:

Sam Goldwasser wrote in
:

Jim Yanik writes:

"Ancient_Hacker" wrote in
oups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either
one can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity
modulation.

Followup: The frequency of the chopped line does NOT correlate with
line frequency.

Perhaps HV oscillator freq?

I don't think so. It's order of a few hundred Hz and not constant.

And I should note that at low intensity, it is worst going full off.
With the intensity turned up, it's not visible. There is minimal
if any geometric distortion of the trace (outside of the focus
problem, which doesn't always appear) so I doubt any LV power supplies
are involved that also feed the amps.

Then you're down to decoupling caps.

It's almost as if the Z input has some oscillation on it. When I
first noticed, I thought maybe the chopped blanking was misbehaving,
but this occurs on all vertical modes.

A thought occurs to me;there's a 1uf/150V(IIRC) electrolytic on the wiper
of the CRT grid bias pot,to ground;that could be going bad.

I'll check that.

It's also related to warmup. At power-on, there is no problem. It
takes a of couple minutes to show up. The fan is running.

And even then, the severity varies randomly.

So, what could affect the Z modulation AND sometimes focus, but not
geometry?

If it was the HV divider I guess a parts unit is the only source for a
replacement?

Yes,it was a TEK-made part,from their defunct hybrid/ICO in-house plant.
Removing a good one from a motherboard without damaging it is not an easy
task

Now it really doesn't like even normal intensity.

But the geometry (beam stiffness, etc.) is not affected. So, I'm
leaning toward a problem in the grid circuit, not the HV itself.

Does anyone know of a free source for decent quality schematics? I have
several complete manuals downloaded from various places but the resolution
of the schematics tends to be terrible and only marginally useful.

I think we have the 465b manual at work, I'll have to check on Mon.
If we do, I'll only be able to copy a couple of pages so I'll just be
able to get the power supply and maybe a few others, but I'll give it
a shot.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

sck0006 writes:

On 18 Mar 2006 12:40:11 -0500, Sam Goldwasser
wrote:

Does anyone know of a free source for decent quality schematics? I have
several complete manuals downloaded from various places but the resolution
of the schematics tends to be terrible and only marginally useful.

I think we have the 465b manual at work, I'll have to check on Mon.
If we do, I'll only be able to copy a couple of pages so I'll just be
able to get the power supply and maybe a few others, but I'll give it
a shot.

Thanks. That would probably be adequate. There's no problem with the text
of the manuals, just the schematics. And this problem would seem to be
associated either with the power supplies or the CRT bias/intensity/Z
input circuits.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Sam Goldwasser wrote:
sck0006 writes:

On 18 Mar 2006 12:40:11 -0500, Sam Goldwasser
wrote:

Does anyone know of a free source for decent quality schematics?
***

Thanks. That would probably be adequate. There's no problem with the text
of the manuals, just the schematics. And this problem would seem to be
associated either with the power supplies or the CRT bias/intensity/Z
input circuits.



I found the 465B manual from bama.sbc.edu is nice: I can read the
schematics easily, and quality is alright for my repair purposes. Sam,
did you try this free source? don't forget about bama mirror at
edebris, for faster download.

Only thing you have to do extra is that you have to install the free
reader, for .djvu format. Even if it is old, it still works adequate.


hth,
Andreas

"Andreas Tekman" writes:

Sam Goldwasser wrote:
sck0006 writes:

On 18 Mar 2006 12:40:11 -0500, Sam Goldwasser
wrote:

Does anyone know of a free source for decent quality schematics?
***

Thanks. That would probably be adequate. There's no problem with the text
of the manuals, just the schematics. And this problem would seem to be
associated either with the power supplies or the CRT bias/intensity/Z
input circuits.



I found the 465B manual from bama.sbc.edu is nice: I can read the
schematics easily, and quality is alright for my repair purposes. Sam,
did you try this free source? don't forget about bama mirror at
edebris, for faster download.

Only thing you have to do extra is that you have to install the free
reader, for .djvu format. Even if it is old, it still works adequate.

That looks much better than the ones I have. Thanks. I knew
about the bama Web site but never bothered to download the djvu reader
before.

Any hints on getting pages to print with reasonable quality?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

On 18 Mar 2006 19:54:37 -0500 Sam Goldwasser
wrote in Message id: :

Thanks. That would probably be adequate. There's no problem with the text
of the manuals, just the schematics. And this problem would seem to be
associated either with the power supplies or the CRT bias/intensity/Z
input circuits.

Check your mail.

On 20 Mar 2006 10:15:33 -0500, Sam Goldwasser
wrote:

"Andreas Tekman" writes:

Sam Goldwasser wrote:
sck0006 writes:

On 18 Mar 2006 12:40:11 -0500, Sam Goldwasser
wrote:

Does anyone know of a free source for decent quality schematics?
***

Thanks. That would probably be adequate. There's no problem with the text
of the manuals, just the schematics. And this problem would seem to be
associated either with the power supplies or the CRT bias/intensity/Z
input circuits.



I found the 465B manual from bama.sbc.edu is nice: I can read the
schematics easily, and quality is alright for my repair purposes. Sam,
did you try this free source? don't forget about bama mirror at
edebris, for faster download.

Only thing you have to do extra is that you have to install the free
reader, for .djvu format. Even if it is old, it still works adequate.

That looks much better than the ones I have. Thanks. I knew
about the bama Web site but never bothered to download the djvu reader
before.

Any hints on getting pages to print with reasonable quality?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

I've got the schematics if you still want them. I was only able to
get horizontal amplifier, crt circuit, power supply, and the power
supply troubleshooting sections. Let me know...

Steve

sck0006 writes:

On 20 Mar 2006 10:15:33 -0500, Sam Goldwasser
wrote:

"Andreas Tekman" writes:

Sam Goldwasser wrote:
sck0006 writes:

On 18 Mar 2006 12:40:11 -0500, Sam Goldwasser
wrote:

Does anyone know of a free source for decent quality schematics?
***

Thanks. That would probably be adequate. There's no problem with the text
of the manuals, just the schematics. And this problem would seem to be
associated either with the power supplies or the CRT bias/intensity/Z
input circuits.



I found the 465B manual from bama.sbc.edu is nice: I can read the
schematics easily, and quality is alright for my repair purposes. Sam,
did you try this free source? don't forget about bama mirror at
edebris, for faster download.

Only thing you have to do extra is that you have to install the free
reader, for .djvu format. Even if it is old, it still works adequate.

That looks much better than the ones I have. Thanks. I knew
about the bama Web site but never bothered to download the djvu reader
before.

Any hints on getting pages to print with reasonable quality?

I've got the schematics if you still want them. I was only able to
get horizontal amplifier, crt circuit, power supply, and the power
supply troubleshooting sections. Let me know...

Thanks but I think what I was able to get from the bama Web site is
quite legible, if a pain to print. Printing from within the djvu reader
results in poor quality, at least with my printer. I now export the
page to a .bmp file and print it in sections. I think all I should need
is the CRT circuit and I've printed that.

I'm just surprised that with all the 465Bs out there, no one has come forward
to say they've seen this problem before.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

On 20 Mar 2006 21:52:38 -0500, Sam Goldwasser
wrote:

sck0006 writes:

On 20 Mar 2006 10:15:33 -0500, Sam Goldwasser
wrote:

"Andreas Tekman" writes:

Sam Goldwasser wrote:
sck0006 writes:

On 18 Mar 2006 12:40:11 -0500, Sam Goldwasser
wrote:

Does anyone know of a free source for decent quality schematics?
***

Thanks. That would probably be adequate. There's no problem with the text
of the manuals, just the schematics. And this problem would seem to be
associated either with the power supplies or the CRT bias/intensity/Z
input circuits.



I found the 465B manual from bama.sbc.edu is nice: I can read the
schematics easily, and quality is alright for my repair purposes. Sam,
did you try this free source? don't forget about bama mirror at
edebris, for faster download.

Only thing you have to do extra is that you have to install the free
reader, for .djvu format. Even if it is old, it still works adequate.

That looks much better than the ones I have. Thanks. I knew
about the bama Web site but never bothered to download the djvu reader
before.

Any hints on getting pages to print with reasonable quality?

I've got the schematics if you still want them. I was only able to
get horizontal amplifier, crt circuit, power supply, and the power
supply troubleshooting sections. Let me know...

Thanks but I think what I was able to get from the bama Web site is
quite legible, if a pain to print. Printing from within the djvu reader
results in poor quality, at least with my printer. I now export the
page to a .bmp file and print it in sections. I think all I should need
is the CRT circuit and I've printed that.

I'm just surprised that with all the 465Bs out there, no one has come forward
to say they've seen this problem before.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Glad you got what you needed. It is a strange problem that you have,
I hope you can track it down. My T-935A has a problem sort of similar
to what you're describing, but it is by no means periodic noise and
seems to be much more like a dirty intensity pot. It has a chopped
appearance, but just looks like dirty pot noise instead of what you're
describing. I haven't had any desire to take it back apart, too many
other things to do. Best of luck.

Steve

Jim Yanik writes:

Sam Goldwasser wrote in
:

Jim Yanik writes:

"Ancient_Hacker" wrote in
oups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either
one can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity
modulation.

It may be.

New followup: I've now got the thing open. Since it appeared heat dependent,
I used a rubber tube to blow on various components in the HV area.
Blowing on the thick film resistor network even immeidately after
power-on and the beam appeared (already messed up) seemed to make a
big difference causing the symptoms to disappear entirely for awhile.
This could not have been heat related because it was within 10 seconds of
powering up so nothing really could get hot. Then, after touching the
thick film assembly perhaps with a few wiggles thrown in, the problem
has disappeared entirely and has not reappeared. I've since cleaned
it with alcohol and I will be running the scope off and on for a few
hours over the next few days on the bench to see what happens.

Of course, the instant I put the cover back on and replace the scope in its
hard-to-reach spot, it will screw up again.

So the working hypothesis is that indeed either contamination or cracked
joints to this part.

If cracked joints turns out to be confirmed with the problem reappearing,
I would probably try conductive silver Epoxy first at each of the
connections to the thick film itself rather than solder. If that
didn't last, then what about fashioning a replacement from discrete parts?
It might be a bit of a challenge to get high voltage resistors to fit in
the space but seems like it could work. It's only 4 resistors, though
admittedly 3 of them are high resistance (6.57M, 25.6M, 24.5M, and 550K)
and at least 2 of them need to withstand almost 3 kV.

Any comments?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Sam Goldwasser wrote in message
...
Jim Yanik writes:

Sam Goldwasser wrote in
:

Jim Yanik writes:

"Ancient_Hacker" wrote in
oups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either
one can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity
modulation.

It may be.

New followup: I've now got the thing open. Since it appeared heat
dependent,
I used a rubber tube to blow on various components in the HV area.
Blowing on the thick film resistor network even immeidately after
power-on and the beam appeared (already messed up) seemed to make a
big difference causing the symptoms to disappear entirely for awhile.
This could not have been heat related because it was within 10 seconds of
powering up so nothing really could get hot. Then, after touching the
thick film assembly perhaps with a few wiggles thrown in, the problem
has disappeared entirely and has not reappeared. I've since cleaned
it with alcohol and I will be running the scope off and on for a few
hours over the next few days on the bench to see what happens.

Of course, the instant I put the cover back on and replace the scope in
its
hard-to-reach spot, it will screw up again.

So the working hypothesis is that indeed either contamination or cracked
joints to this part.

If cracked joints turns out to be confirmed with the problem reappearing,
I would probably try conductive silver Epoxy first at each of the
connections to the thick film itself rather than solder. If that
didn't last, then what about fashioning a replacement from discrete parts?
It might be a bit of a challenge to get high voltage resistors to fit in
the space but seems like it could work. It's only 4 resistors, though
admittedly 3 of them are high resistance (6.57M, 25.6M, 24.5M, and 550K)
and at least 2 of them need to withstand almost 3 kV.

Any comments?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

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Some woven glass sleeving , cut to required lengths and formed into a
compressable and insulated pad or more pads if you cannot localise better
and cautiosly compressed by cable tie/s around the thick film ?
I've only done similar on low V SM ICs that are covered in black epoxy ,
boards as well, so impossible to re-do the SM solder , to the ceramic
boards, and is a throw away job otherwise.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Sam Goldwasser wrote in
:

Jim Yanik writes:

Sam Goldwasser wrote in
:

Jim Yanik writes:

"Ancient_Hacker" wrote in
oups.com:

Oh, there's also a big voltage divider resistor (the white
ceramic thing) Any moisture, dust, or leakage there and you
tend to get unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback
for regulation on one side,and the CRT focus divider on the other.
Either one can go out-of-tolerance,and the metal pins can crack
and be intermittent.I've never been successful in resoldering
them,either.

I do not think this part would be the cause of his intensity
modulation.

It may be.

New followup: I've now got the thing open. Since it appeared heat
dependent, I used a rubber tube to blow on various components in the
HV area. Blowing on the thick film resistor network even immeidately
after power-on and the beam appeared (already messed up) seemed to
make a big difference causing the symptoms to disappear entirely for
awhile. This could not have been heat related because it was within 10
seconds of powering up so nothing really could get hot. Then, after
touching the thick film assembly perhaps with a few wiggles thrown in,
the problem has disappeared entirely and has not reappeared. I've
since cleaned it with alcohol and I will be running the scope off and
on for a few hours over the next few days on the bench to see what
happens.

Of course, the instant I put the cover back on and replace the scope
in its hard-to-reach spot, it will screw up again.

So the working hypothesis is that indeed either contamination or
cracked joints to this part.

If cracked joints turns out to be confirmed with the problem
reappearing, I would probably try conductive silver Epoxy first at
each of the connections to the thick film itself rather than solder.
If that didn't last, then what about fashioning a replacement from
discrete parts? It might be a bit of a challenge to get high voltage
resistors to fit in the space but seems like it could work. It's only
4 resistors, though admittedly 3 of them are high resistance (6.57M,
25.6M, 24.5M, and 550K) and at least 2 of them need to withstand
almost 3 kV.

Any comments?

I've wondered if low melting point solder like what comes in the ChipQuik
desoldering kit might work on thick-film connections.It wasn't available to
me at Tek.The conductive silver epoxy may be a better idea. Trouble if you
have to resolder the thick-film back into the motherboard.

Alternately,you could fashion a small PCB to fit where the thick film
goes,and solder your resistors to the PCB. I've not tried this,though.

--
Jim Yanik
jyanik
at
kua.net

On 26 Mar 2006 12:35:51 -0500 Sam Goldwasser
wrote in Message id: :

I used a rubber tube to blow on various components in the HV area.

OK, I'm assuming you've found a way to heat the air first. I'm interested
in this setup - could you elaborate?

JW writes:

On 26 Mar 2006 12:35:51 -0500 Sam Goldwasser
wrote in Message id: :

I used a rubber tube to blow on various components in the HV area.

OK, I'm assuming you've found a way to heat the air first. I'm interested
in this setup - could you elaborate?

In this case, it wasn't a matter of heat. It turned out that simply air flow
made the difference since this occurred immediately after power on before anything
had a chance to heat up.

If I had to provide heat, a blow dryer would have been my tool of
choice

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Sam Goldwasser wrote in
:

JW writes:

On 26 Mar 2006 12:35:51 -0500 Sam Goldwasser
wrote in Message id: :

I used a rubber tube to blow on various components in the HV area.

OK, I'm assuming you've found a way to heat the air first. I'm
interested in this setup - could you elaborate?

In this case, it wasn't a matter of heat. It turned out that simply
air flow made the difference since this occurred immediately after
power on before anything had a chance to heat up.

If I had to provide heat, a blow dryer would have been my tool of
choice

Note that your breath will have high levels of moisture in it,that could
alter the conductivity of the thick-film elements,especially if the thick-
film is dirty.

I used to use an ordinary hairdryer(folding travel style) at low heat,until
one of the cleaning people stole it.(along with my TI-30 calculator)

a paper cone narrowed the air flow to what I desired.

--
Jim Yanik
jyanik
at
kua.net

Jim Yanik writes:

Sam Goldwasser wrote in
:

JW writes:

On 26 Mar 2006 12:35:51 -0500 Sam Goldwasser
wrote in Message id: :

I used a rubber tube to blow on various components in the HV area.

OK, I'm assuming you've found a way to heat the air first. I'm
interested in this setup - could you elaborate?

In this case, it wasn't a matter of heat. It turned out that simply
air flow made the difference since this occurred immediately after
power on before anything had a chance to heat up.

If I had to provide heat, a blow dryer would have been my tool of
choice

Note that your breath will have high levels of moisture in it,that could
alter the conductivity of the thick-film elements,especially if the thick-
film is dirty.

Could be part of the effect. Anyhow, it is still stable today.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.