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Got an old oscilloscope, some display problems

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allanw:
I got an old Philips PM3256 75MHz scope as I mentioned in my last thread. Everything's mostly working fine, except it seems like the trace sometimes gets "stuck" at either the 2nd from the left or 2nd from the right vertical line. When this happens everything seems to get scrunched up (bright dot), as if it had hit the edge of the screen and stopped drawing. The problem randomly comes around and goes away, but it's mostly stuck like the second picture I'll attach. Here's some pictures (intensity levels changed as I took pictures):

Everything good:


Scrunched up 20% from the right (note bright dot where it stops drawing):


More scrunching:


Sadness:


It's not just me being dumb and having the horizontal shift on wrong or something, it simply won't draw past a certain point sometimes. Also, it isn't permanently stuck, as sometimes I see it flash and actually draw the whole way through. Other times it'll actually stay at 90% or 100%, which is usable. Also, it happens no matter what trigger mode or channel or anything that I set.

Anyone have some advice? I did obtain the service manual for this so I'll take a look through that.
edit: here's a video which will work after it's processed:


Pyr0Beast:
Dry or cold joint somewhere probably, not sure tho. Does it do that when it is still cold or when it warms up ?

Might be even something with deflection. Won't hurt to open it up :)

mkissin:
If it's an old CRT scope having deflection problems, my first port of call would be changing all of the electrolytic capacitors in the CRT drive circuitry. Check for any that look suspect first, and if that doesn't help, replace the lot. Even if they aren't dead, it's good insurance.

MoJo:
I have the same issue with the same type of CRT, by that I mean from Phillips/ Fluke ... mine is an old PM3094. The CRT is old and worn out ... it has burn-ins and is quite dim on default settings. Now I asses the issue to be a couple of causes, one being an old CRT, second being that these solid Scopes have an achilles heel being electrolytic caps which over the years are not good anymore. As another person suggested it would be wise to start their. Third cause is that these Phillips scopes tend to run hot, over the years it may have done heat damage to the board and it's components. I opened mine and saw that the board is browned/ baked at certain areas, ie. the power board, and the CRT control board ... two areas that deal with high voltage.

My scope at times has perfect horizontal tracing, and at other times has 2/3rd tracing. It doesn't seem to be temprature related as I have started and restarted at times with high working tempratures, and the result still varies ... sometimes perfect and others not so. My suspicion is that this is a charge issue, relating to old worn out caps. Lastly replacing the screen is quite difficult on the Flukes, as they are quite hard to find and sometimes expensive ... requiring the buying of an entire non functional unit just to salvage it's screen. Facing this I bought the Rigol, and consider my options ... I suggest you do the same.

allanw:
It seems to start and stop randomly. If I'm lucky it'll be perfect for a long time.

I'll try recapping the power and CRT drive sections. It's actually pretty cheap to do, and hopefully I won't break the scope in the process.

At least my screen is very good. Who knows how long that'd last though. Question: does keeping it on lower intensity settings preserve the life of the screen longer?

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