Zenith 25EC58 Restoration Thread

[TinCanAlley]

Originally Posted by BeamT

Horiz ringing and jail bars in my experience can be very difficult to troubleshoot. Sometimes I've had good luck with a scope, if you want to try that route. The source can be a number of places and can be very subtle. Otherwise I have had some success examining one circuit at a time. I try not to just throw parts at it.

To finish where you left off, I would look at:

C258 10uf 50v B+ Horiz Module (you mentioned above)
C264 47uf 10v Secondary Horiz Drive Transformer

and then work your way through the horiz blanking and then into the video path. This could easily be caused by horiz blanking.

I find it helpful to work with a blank raster, from a known good generator, tuner mid channel, or IF disconnected. Chromatic switch off, color off. This eliminates any outside source issues and gives you a good baseline.

Has this set always had the jail bars? Has the tripler been replaced? Zeno (RIP) always commented on non-Zenith HV triplers causing Jail Bars. I never encountered this but after replacing a separate tripler and focus divider in a 25DC56 with a Zenith combined unit 977-36, I ended up with jail bars. Putting the separate tripler and divider back in, eliminated the jail bars.

What part of the CM-122 Set-up procedures are you looking for? or all of it.

Safety first, the boost circuits is these sets are not only at a higher voltage, they can deliver some current, lots of RF energy.

This set has always had jail bars to some extent. It was initially recapped because of other odd video issues associated with bad caps. Once the recap was done, the bars were more noticeable once brightness and contrast were set.

I have replaced C258 with the SM replacement part from Vishay. C264 tested good with and ESR around 430 milliohms and a value of 45. I have a replacement, just in case.

I've been trying to figure out where to inject the signal from my generator, but lack the knowledge of where in the circuit to inject it and what I need to disconnect when doing so.

Years ago, you can search for them, I posted quite a bit during the initial repair and search for ringing source. I used the scope of many areas and found ringing in a couple, but was told that it wasn't the cause of an issue. Found it in the brightness limiter circuit, HOT base and B+, but I was pretty new with the scope and I went with it not being the jail bars. The waveforms in the Sams aren't the highest quality, but enough to note difference is what I got.

The set has the original tripler. Only thing it need was the focus divider and I got an NOS and it's been fine ever since.

Once the set is back up and running, it's going to need some adjustments, so I thought I'd run through all the adjustments for AGC, ACC, APC, brightness limiter, color killer, convergence (static and dynamic), etc. Not going to mess with the IF stuff, just the basic stuff. Just wondering if the factory SM has the same procedures.

Thanks for all you time and help!