MCR Power supply troubleshooting guide?

gamefixer

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On monday I dug out of my garage this Tron I've been holding onto. During the year or so that I've had the machine I managed to end up with 4 power supply boards. Since I only needed one I sold three of the others. They were all sold to me working with Bob Robert kits and Lithium batteries installed.

Now that I'm down to one supply I cant for the life of me get the +5 to come up correctly. With or without a load I only get +3.5 or so. The VR makes no difference in voltage and the board already had a Bob Roberts rebuild kit installed. I've gone over the traces in the +5 section numerous times and cant see anything wrong. I've swapped transistors with the +12 section and the problem stayed in the +5 section.

This very same machine worked fine with the other three supplies so I know that my problem is within the power supply board.

Anyone have any experience with this sort of thing? I really dont want to have to install a switcher so I have a friend sending me another board. That said I hate to be stumped by a stupid power supply board.

Thanks guys!

Matt
 
The reset circuits are problematic. You can test for this by grounding the base of Q201. If the game works great when you do this, the problem is in the reset circuit. If no change, keep looking :)
 
The reset circuits are problematic. You can test for this by grounding the base of Q201. If the game works great when you do this, the problem is in the reset circuit. If no change, keep looking :)

My problem is in the +5 section. I have the reset wire pulled so even if it was stuck it wouldnt get back to the game board. I think I'm going to have to pull all of the parts off the board and bead blast or sand blast it. There is way too much corrosion on the board for anything to make a good solid connection.

Matt
 
when you figure it out lmk i have the same damn problem. I gave up and put in a arcadeshop switcher with a heavy duty happ ps.. works perfect and NO HUM
 
when you figure it out lmk i have the same damn problem. I gave up and put in a arcadeshop switcher with a heavy duty happ ps.. works perfect and NO HUM

I was thinking about the AS adapter and a switcher but I had mixed results with them a few years ago. One Tron worked great. Another Tron and a Spy Hunter, not to great.

I've been pulling a few parts off at a time and actually taking a sanding sponge to the board. I've managed to get the +5 to come up but it craps out after about 30 minutes, or right when I get to about 150k :) . I know its not a good idea to strip the board of all the solder masking but I have to guess that exposed copper for a short period of time is better then acid slowly eating away at the board.

I've never re-masked a board before. Anyone have any pointers or ideas? I'd like to protect whats left of the copper after I blast the board.

Matt
 
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