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Author Topic: Tektronix 608 XY Monitor - extra trace mystery  (Read 20922 times)

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Offline skeletonmeatTopic starter

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Tektronix 608 XY Monitor - extra trace mystery
« on: April 11, 2024, 02:15:48 am »
Hi all,

Here with a mystery - I'm not the most experienced with this, so I hope I'm being dumb and it's an obvious fix!

I have a Tek 608 XY Monitor that is mostly working normally, but has an additional static trace on the monitor (slightly off-center) at all times when powered on. The normal trace works correctly. The static trace responds to the Intensity and Z gain pots (although it's intensity is offset slightly higher than the normal trace), but not the X & Y offset pots, and its position is not affected by the input signal. The static trace is tied to the normal trace; i.e. when the trace is offset from the static trace by input signal or pot offsets the monitor will act a bit like a ramp is being input into X or Y.

Hopefully this is more clear with pictures - these are a few of the display with the X&Y offset changed, but no input signal at all.

Does anyone have any clues for what's going on here? My best guess is that the deflection amp is getting some kind of V constantly from somewhere, but I don't really know! If anyone has any pointers for repair, I'd really appreciate it! It's a nice monitor, and I'd love to get it working correctly.
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Offline CaptDon

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Re: Tektronix 608 XY Monitor - extra trace mystery
« Reply #1 on: April 11, 2024, 01:00:47 pm »
It would appear that perhaps you have an open filter capacitor on one of the supply rails producing a large A.C. voltage riding on top of a D.C. supply rail.
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Collector and repairer of vintage and not so vintage electronic gadgets and test equipment. What's the difference between a pizza and a musician? A pizza can feed a family of four!! Classically trained guitarist. Sound engineer.
 

Offline jonpaul

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Re: Tektronix 608 XY Monitor - extra trace mystery
« Reply #2 on: April 11, 2024, 01:17:56 pm »
damaged CRT?
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Offline skeletonmeatTopic starter

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Re: Tektronix 608 XY Monitor - extra trace mystery
« Reply #3 on: April 11, 2024, 05:58:07 pm »
Quote from: CaptDon on April 11, 2024, 01:00:47 pm
It would appear that perhaps you have an open filter capacitor on one of the supply rails producing a large A.C. voltage riding on top of a D.C. supply rail.

What would you recommend to troubleshoot this? I don't have a ton of experience with HV, but would it make sense to try and replace the large electrolytic caps on the supply board? I've repaired a scope before, but it was just some pretty obvious LV caps in the defraction amp section. I worry about this being over my head/slighty dangerous
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Offline skeletonmeatTopic starter

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Re: Tektronix 608 XY Monitor - extra trace mystery
« Reply #4 on: April 11, 2024, 06:01:39 pm »
Quote from: jonpaul on April 11, 2024, 01:17:56 pm
damaged CRT?

Maybe? I lean towards no because the extra trace looks right? It isn't showing any crazy bloom or dead/burned spots
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