Zenith 25EC58 Restoration Thread

[TinCanAlley]

Since I'm starting from scratch, I'm creating my final thread on this chassis/TV. I know multiple threads are frowned upon and that's why this one. It will serve as an update and help request in a single thread.

Okay, so I am tired of chasing issues, so I'm going to tackle the entire set, piece by piece. I'll start with the chassis and replace all electrolytics. I did that 13 years ago, but I know a little more about replacements than I did back then. I have ordered, where available, the exact replacement noted in the SM (Vishay and Cornell). I will also be testing, as best as can be while in circuit, all resistors and diodes.

My first task is to measure B+ and scope it. I will start at the test point and from there, test and scope at all the in and out points on each module. From the schematics I see that from the regulator it goes in this order: Chroma-->Subcarrier-->Video Processor-->Vertical-->Horizontal-->125V source for a complete loop. I want to do this before and after recapping and other diags to see if there is any noticeable change. I figure if it starts out clean, then gets noisier, I can pinpoint the issue better.

After the main stuff, I'll be replacing pots on the convergence board with NOS, replace IC on sound board in hopes of getting tone control back and fixing the channel motor as it gets stuck pretty often and requires a change up and down to get it to fully change channel. Once that is done, I'll do all adjustments per SM.

So that's my plan. Parts will be here Thursday, so I have plenty of time to measure and scope. I know I'll be here often to ask questions and request help, that's for sure. I've learned quite a bit from everyone here, so I think this will go well.

Now for my first questions. If the B+ is 125V, does that need to be dead on, or is there a +/- that's acceptable? The filtering comes from the multi-cap canister that I bypassed already, wanting the keep the canister for aesthetics. I wasn't able to find 400uf 150V, so I used 390uf 160V. I'm pretty sure that falls within the 20%. See attached pic.

Do the RGB output transistors have affect on image and such? The reason I ask is it originally came with 121-743 TO-5 package, but to replace one cost more than buying all three 121-868 TO-220 package. While this works, I miss the original look of the heatsinks with the plastic cage. As it stands now, they are just plugged in with a small clip-on heatsink on each. Looks crappy. If they do the exact same job, I'm going back as I got my hands on an NOS TO-5.