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Adventure in tracing down jitter


mongteen@...
 

Hello,

I have a RM31a that has a 54x CRT that works reasonably well. Thanks
Dean :) There is a slight horz. jitter about 2mm worth. So I check
the left deflection pin and see that there was no jitter. I check the
right deflection pin and see jitter. So I go about measuring and
changing tubes associated with the right deflection pin. Then I
sleep on it for a while. It occured to me to check for jitter at very
low sweep speeds. I connect my 7704a to the right deflection pin set
the coupling to AC and volia I found that the jitter is 120 Hertz. So
I measured the 500 V supply and found ripple of about 1 volt PP. So I
added a small cap to help filter out the ripple and the jitter is
gone!

The moral of the story is that alway check the PS first! I fell in to
the trap of seeing that everything else worked OK and assumed the PS
was OK.


Windsor


Don Black <jeans@...>
 

Hi Windsor,
You seem to have found the source of the jitter however I
think you're working around the fundamental problem with your small bypass
capacitor.
Check the regulated power supply, perhaps the main filter capacitors are
weak, allowing too much ripple before the regulator or the regulator tubes
could be weak and saturating, passing the ripple.
If it's got selenium rectifiers they may be getting weak, not supplying
enough voltage or the regulators to work. Replace them with silicon diodes
with added series resistors to compensate for the higher efficiency of the
silicon diodes.
Your bypass capacitors might be a cheap way of working around the problem but
be prepared for it to get worse and you'll have to look further.
Don
Black.
PS check the mains voltage settings match the local supply, if it's set for a
higher voltage than your local supply so the set's not getting enough supply
voltage that could cause it to drop out of regulation.

mongteen@excite.ca wrote:

Hello,

I have a RM31a that has a 54x CRT that works reasonably well. Thanks
Dean :) There is a slight horz. jitter about 2mm worth. So I check
the left deflection pin and see that there was no jitter. I check the
right deflection pin and see jitter. So I go about measuring and
changing tubes associated with the right deflection pin. Then I
sleep on it for a while. It occured to me to check for jitter at very
low sweep speeds. I connect my 7704a to the right deflection pin set
the coupling to AC and volia I found that the jitter is 120 Hertz. So
I measured the 500 V supply and found ripple of about 1 volt PP. So I
added a small cap to help filter out the ripple and the jitter is
gone!

The moral of the story is that alway check the PS first! I fell in to
the trap of seeing that everything else worked OK and assumed the PS
was OK.

Windsor

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Stan or Patricia Griffiths <w7ni@...>
 

If you have identified the bad filter cap, I probably have a good salvaged
replacement that you can have for a few bucks. Let me know.

Stan
w7ni@easystreet.com

mongteen@excite.ca wrote:

Hello,

I have a RM31a that has a 54x CRT that works reasonably well. Thanks
Dean :) There is a slight horz. jitter about 2mm worth. So I check
the left deflection pin and see that there was no jitter. I check the
right deflection pin and see jitter. So I go about measuring and
changing tubes associated with the right deflection pin. Then I
sleep on it for a while. It occured to me to check for jitter at very
low sweep speeds. I connect my 7704a to the right deflection pin set
the coupling to AC and volia I found that the jitter is 120 Hertz. So
I measured the 500 V supply and found ripple of about 1 volt PP. So I
added a small cap to help filter out the ripple and the jitter is
gone!

The moral of the story is that alway check the PS first! I fell in to
the trap of seeing that everything else worked OK and assumed the PS
was OK.

Windsor

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--- In TekScopes@y..., Don Black <jeans@n...> wrote:

If it's got selenium rectifiers they may be getting weak, not
supplying
enough voltage or the regulators to work. Replace them with silicon
diodes
with added series resistors to compensate for the higher efficiency
of the
silicon diodes.
Even the Selenium Rectifiers aro OK (at this time), REPLACE them!
Often they fail suddenly with a short and not in any case the fuse(s)
blown fast enough to prevent damage to the transformerwinding(s)!!!

Seen those often enough... (not only in Scopes)

Jorgen
dj0ud


richg_1998@...
 

Hi Windsor
Your Email address no longer works. I hope you have sent the tek 475
fan. Let me know.

Richard




--- In TekScopes@y..., mongteen@e... wrote:
Hello,

I have a RM31a that has a 54x CRT that works reasonably well.
Thanks
Dean :) There is a slight horz. jitter about 2mm worth. So I check
the left deflection pin and see that there was no jitter. I check
the
right deflection pin and see jitter. So I go about measuring and
changing tubes associated with the right deflection pin. Then I
sleep on it for a while. It occured to me to check for jitter at
very
low sweep speeds. I connect my 7704a to the right deflection pin
set
the coupling to AC and volia I found that the jitter is 120 Hertz.
So
I measured the 500 V supply and found ripple of about 1 volt PP. So
I
added a small cap to help filter out the ripple and the jitter is
gone!

The moral of the story is that alway check the PS first! I fell in
to
the trap of seeing that everything else worked OK and assumed the PS
was OK.


Windsor


dhuster@...
 

Windsor, you discovered the fundamental truth we were always taught
in Navy "A" school. Always check the power supplies first.

And Don, bless his generous Aussie heart, is correct also: you're
not fixing the problem -- you're getting rid of the symptom. Always
assume the original circuit worked great at one time and fix the
problem so that the orignal circuit works great again.

We had a tech in the Dallas Service Center who "re-engineered" the
front end of a sampling system to get it to work. I couldn't believe
the supervisor didn't rain fire and brimstone on him, but I don't
think the supervisor knew about it. Maybe he got the sampler to
work, but I pity the technician who had to work on that thing the
next time!

Dean (and you're welcome for the CRT)