I F***ed Up... Help, 25" Amp Deflection

Todd31

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I F***ed Up... Help, 25" Amp Deflection - SOLVED

I wasn't paying close enough attention when I plugged in the deflection board. I had the yoke wire unplugged. I grabbed the wire at the connector and got zapped by it. I now only have the lower right quarter of the screen. I am thinking I hosed the yoke. Is one quarter screen a symptom of a messed up yoke? I replaced all 8 transistors that go on the heatsink since they were old anyways and nothing changed.
 
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Someone more knowledgeable will chime in I'm sure, but yokes are just a bunch of wire, you probably didn't destroy it... you've messed up something on your deflection board.
 
Possibly from not having the yoke hooked up I guess. I will continue diag and see what I come up with.
 
Ok, well you must have correct voltages (+25VDC and -25VDC) because you have some image on the screen

Time to narrow it down

Which portion of screen works?
 
The yoke must be OK, as there is something on the screen

Right bottom OK means the Positive X, and the negative Y is working properly

So the entire circuit surrounding Q16 (Horiz Pos) and Q7 (Vert Neg) are working

Look at this diagram. A part in the other 2 circuits has failed (Either Q6 or Q17 circuits)
Since you have changed them parts it must be a part/s earlier than this final stage of amplification
Try Q's 11, 12 or 13 or counterparts Q's 1, 2 or 3

Double check your repair work also by the way, ensuring the correct parts went in the right order :)
 
I replaced q1,2,3,11,12,13 with some new 2n4124 transistors I had laying around and I had no change. I have used those as a cross in the past with no issues. All of my other work is sound. The hunt continues. That schematic is nice. Thanks for that. Once I figure out the issue I will post the fix. Damn, this is frustrating because usually these boards are easy to fix with the ways the commonly fail and I want to play Star Wars!
 
Are all of your Zero ohm resistors replaced with solid links?

There are a few in the yoke line :)

They are meant to be solid (Early day mod, some slipped through to modern day)
 
Problem solved! I had two non conductive nuts on the large transistors on the heatsink. These were not making contact with the base to the board.

I fixed another guys parts board and since I had my board out to test his I replaced his missing ones with mine. Then I found some that fit mine later. Oops! Simple fix, just overlooked it.

Thanks for all the help. I should have tested that contact when I did the transistors. The fact that I shocked myself then had an issue sent me and you all on a wild goose chase! I don't get zapped then I go after the nuts first.

2012-08-05_18-32-15_921.jpg
 
It's so basic, I hadn't even thought about something like that.....at least I was close (physically) ;) Nice to see it's back. Is it your camera or does the text look really that purplish ?
 
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