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Vectrex plays blind

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Help me troubleshoot this Vectrex. It plays blind. I hear sound, the controls work. I do not hear the tale tell buzz of the Vectrex or the crackle when I turn the volume knob. But I can adjust the colume. And I do see neck glow through the top vent holes. I should mention that when I turn the brightness pot, I feel like the board it is attached to is loose. Although the pot itself seems securely mounted to the board.


The Vectrex is very clean! It looks and feels brand new. So I doubt it was the subject of any abuse.


I haven't taken it apart yet. But I thought I would get some advice from the experts first.




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The Vectrex buzz came back. I originally thought it was because I cleaned a connector, but I think it just comes and goes. The diodes tested good. The power levels at various places on the board tested good. I just went down the list in the troubleshooting guide. Eventually, as I was looking for test points for the 9v power, I discovered some corrosion on a solder point. Close examination revealed a bad cap. I identified the bad cap as C513 (on the power board). I've ordered a cap kit from Console5. In the meantime, I need to clean the stuff off the board that leaked out of the capacitor. I suspect the two smaller caps above it are also bad. Depending on what's included in the cap kit, I'll replace what I can.



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Update. I've been sending in regular updates on the FB page, but I feel like it should be documented here. So here are the highlights:


I've replaced the five large caps on the power board (C513, C109, C117, C118, C119), including the one pictured above. Still the same problem.


I checked EP105-104 and EP105-106 and I am getting 10.4 VAC instead of 8.6. But it matches up the same with my working Vectrex. I am guessing 10.4 VAC is the US version and 8.6 VAC is for EU version? Can somebody verify this?


I removed and re-seated the 4066 IC then the screen came alive! See photos.



The vectors are still messed up. Either I get a dot with hairs or some messed up geometry. It's never the same thing twice. If I turn it on and get no vectors, no amount of waiting will make them appear. But if I switch it off and back on again, I may see vectors... although messed up. And then If I do it again, I may see vectors that are fairly normal, but too bright... or is it faint? I see the dot in the middle and spiderwebs, but if I turn brightness down to make the dot disappear, everything else goes away too. So I guess too faint.


I then swapped out some of the IC chips (IC301, IC302, IC208) and have good reason to believe they are all good.


Somebody on the forum suggested that I check the RAM. I cannot swap it out because it is soldered in working Vectrex. But after thinking about it, I reasoned that the RAM must be good. After all, the game plays fine blind. Even when the vectors are partially working or not working at all, I hear sound and it responds to the controller.

Furthermore, I have
good reason to believe that the MC1408-P8 DAC (IC301), 4052B CMOS MUX (IC302), and AY-3-8912 (IC208) are good, since I was able to swap them out with a working Vectrex.

Could the two op amps (IC303 and IC304) be bad? Maybe. The unit produces vectors sometimes, but they seem weak and distorted most of the time. But BOTH op amps?

Could the 4066B BI switch (IC305) be bad? Maybe, but it's not behaving consistently. I'd feel more sure if it did the same thing all the time. I cannot swap it out with my working Vectrex because it is soldered in.

With all this in mind and looking at the schematic, the integrator caps come into question. I know caps are prone to going bad, but ALL of them? I ordered a set of integrator caps from Console5. I should get them Tuesday.



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