Repair Log: Funny WG 6100 story

DWJ

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Symptom #1: new-to-me Wells-Gardner 6100 vector monitor powers up, HV crackles, vector chatter is quiet, picture is heavily distorted, about 2" square.

Problem is replicated when using a known good deflection board.

All six chassis transistors look like transistors when ohmed out.

(After rebuilding the HV power supply, symptoms recur. While adjusting B+ to 180V, observed smoke from wires connected to deflection transistor sockets.)

Solution #1: Look more closely at all six 2N3716s... wait, what?

Fix #1: Replace three 2N3716s with 2N3792s, so that the correct deflection transistors are actually paired. *facepalm*

When in doubt, check the obvious stuff twice.

Symptom #2: monitor powers up, spot killer off, picture heavily distorted. X deflection is good (fullscreen), Y deflection is poor (a 2" vertical strip).

Observed R602 still reads 390 ohms, but is charred. Q603 is open from emitter to base.

Replaced R602, Q603, which were likely killed due during the first round of debugging with the bogus pair of 2N3716s. Loosened, cleaned, applied heatsink compound to Q603/Q604/Q703/Q704. Monitor now works fine.

As a precaution, also replaced Q100/Q101, and small capacitors C102/C103, because they took similar abuse when the monitor was being tested with the bogus 2N3716s.

(Interestingly enough, the bogus 2N3716s tested OK despite the abuse, and worked just fine when I cleaned/reapplied the heatsink compound and mica insulators for the three correctly-installed 2N3716s.)
 
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Had the HV and Deflection board rebuilt, then experienced expanded x-axis/ blooming. Next day, had Vertical Collapse. Replaced all 6 transistors, matching numbers as I went, re soldered one broken wire and now the spot killer comes on immediately. It worked fine after the rebuild and then suddenly bloomed/expanded and hasn't been right since.
 
Had the HV and Deflection board rebuilt, then experienced expanded x-axis/ blooming. Next day, had Vertical Collapse. Replaced all 6 transistors, matching numbers as I went, re soldered one broken wire and now the spot killer comes on immediately. It worked fine after the rebuild and then suddenly bloomed/expanded and hasn't been right since.

In the spirit of eliminating the obvious:

1) Do all 6 of the chassis-mounted transistors "look like transistors" when you test them for voltage drops? (that is, the same pattern of "open" or "about 0.4 to 0.6 volts of drop" for each type - NPN or PNP - of transistor)

2) Any shorts between the wire going to the transistor socket?

3) Any transistors shorted between the body of the transistor and the monitor chassis?

4) Any fuses blown?

On to the less-obvious, but also important: Have you reflowed the solder on the connectors for:

5a) P700 (X), P600 (Y), P701 (yoke)? (and as a precaution, P100 and P101) All the inserting/removing of the wires leading to the deflection/power transistors could have broken a weak solder joint.

5b) Pins for transistors Q603/Q604, Q703/Q704? The heatsinks for those four transistors in are held to the board by nothing more than small solder masks on the back of the board; if the heatsinks are wobbly, those solder joints are cold, and it's possible that the wobbling has given you cold solder joints.

6) Any evidence of smoke/damage to any of the resistors in R6xx and R7xx? How about diodes that might be shorted out? (Do the voltage drops between the pins of the transistors you reflowed in 5b "make sense", or are there shorts?)

I've encountered cold solder joints on multiple deflection boards, so if I were a betting man, if I were to eliminate 1 through 4 (I'd pay real close attention to #2, given that that's where you were working when things failed), I'd bet that it's a cold solder joint that you'll find/eliminate when you get through 5a) and 5b). Of course, that's no guarantee that the failure didn't damage something else, which is why it's a good idea to look very closely for evidence of other damaged parts.
 
Can I send mine to you? *sigh*

I haven't gotten to your thread yet, but it looked like your game wasn't running, which wouldn't let your monitor run.

And you can always send it to me, too. I fixed Frizz's. I can fix yours...
 
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