Are These Circuit Traces Bad

[Findm-Keepm]

Originally Posted by TinCanAlley

Thanks. The part # is: 121-755

I bought these off ebay and they were noted as being NOS. They sure don't look used and are a newer cream colored board instead of the old brownish (I'm so bad with any color other than primaries). The boards are the updated versions of the originals, but they can't be much newer as they also have plug in transistors.

Zenith may have had a second production run, as many shops ordered modules but failed to turn in duds. I remember PTS and others would issue a hotlist if modules they would buy at the dud price, to develop sufficient stock. Zenith System 3 modules were that way in the early 80s - some modules were backordered to the factory to get replacements. We fixed all of ours, so we never swapped anything but tuners and tuner controls. Duramodules (the Zenith term for your module) were exchanged, as the modules were cheap, and Time-to-repair was greater.

I'll check in the morning and see if I have your transistor.

Cheers,

[TinCanAlley]

Okay, the new boards aren't cream color (I was going from memory). They're actually white and green. Here's a pic of the one I installed. The bad transistor is the one with the screw hole just behind large orange capacitor.

[DaveWM]

so you still did not look into the horz blanking? that would have been the 1st place I would have checked.

[zeno]

Originally Posted by DaveWM

so you still did not look into the horz blanking? that would have been the 1st place I would have checked.

Yes lets get back to the jail bars ! The filter can was a good learning
experience but as I suspected unneeded..............
The Sams is in front of me & I am redy to rock & roll !

73 Zeno

[DaveWM]

is this the 25dc56? I assume so,

I would look at the diode and blanking transistor, as well as the voltage divider in front of that.

Scope the fly pulse all the way thru the two blanking transistors.

[TinCanAlley]

I'm doing the best I can. I'm new to this and am doing the things I can do/know how to do. If those don't work, then I can start to tackle the harder things. I don't own a scope, so I'll have to borrow one. I've read through the SM and don't fully understand how to test the blanking circuit, etc.

I'm willing to go all the way in testing an fixing you you're willing to help and understand I'm pretty new to all this.

My first fix is to undo something I just did. If this problem sounds familiar, yell. After changing the horizontal board and caps, I now have a strange effect on the screen. It's hard to explain, but I think if you've seen it before, you'll understand. There are invisible waves rolling diagonally across the screen towards the upper left corner for a moment. They then stop and reverse direction rolling down towards the lower left. They stop again and reverse. The closest I can give an example of is when you're adjusting the APC to get the movement out of the color bars, except these aren't colors rolling, just invisible waves. I'm not sure if it's the what I did, or some other interference that's being introduced.

The chassis is the 25EC58 and if you want to point to things to test/replace, please fire away!

Thanks!

[DaveWM]

you need to deal with one problem at a time.

sounds like some kind of interference, make sure you are not setting a RF source near the set (like a DVD player on top of the tv) try a different signal source, double check that you have everything hooked up right (300ohm to 75 ohm balun) make sure you have not messed up lead dress inside the tv (crt wires, HV wires,tuner IF link). All grounds are in place.

Shot gun repairs often introduce new problems making diagnosis a more difficult problem. don't take it personally, a lot of peeps seem to think replacing every cap in sight will fix everything. It has been my exp that most sets from the mid sixties on do NOT require a lot of cap replacement, and doing so just introduces possible new problems.

So on to the existing problem without a scope its just a guess that the horz blanking is a problem causing the jail bars. if you have the schematic you should be able to find the diode that feeds the pulse to the blanking transistor. I do not know if its on a modual or chassis mounted. On the 25DC56 its NOT on the modual.

[DaveWM]

CR 201 on the schematic