Crazy MCR Power Supply Issue = Head + Brick Wall + Brick Wall + Brick Wall...

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Crazy MCR Power Supply Issue = Head + Brick Wall + Brick Wall + Brick Wall...

The 5+ on my MCR 90412D stopped working again (only outputting +3.45), so I bought new parts for anything that hadn't been replaced even if it "tested good".

I replaced the parts one-at-a-time, then tested the board, starting with the U2 controller -> Q105 -> Q104 -> Q103... Nothing changed. Parts 2,3,4,5,6,8,9,10,11 (pic1) have been replaced at this point.

I read Jacklick's post (https://forums.arcade-museum.com/showpost.php?p=3565917&postcount=3) mentioning replacing tantalum cap 107 with an electrolytic, so I put a real nice 100uF 50V in.
The board put out +5.25 for about a second, then dropped sharply to +3.45 kind of like I'd blown something in the circuit.

I replaced C107 with a standard 100uF 16V electrolytic, but the output was still +3.45.

As a last attempt with C107, I grabbed a tantalum C107 from a donor board, but it still output +3.45.

Back to square one. I replaced U2 and the +5 acted like it was trying to level out, but never reached +5v, then fell back to +3.45.

Since then, I've replaced Q105 -> Q104 -> Q103 with new ones (just in case one of them were bad), but still only +3.45v.


On the LAST attempt, I just happened to leave the meter connected after powering down the 90412D. While measuring at C106, the power initially went to +4.38v then fell back to +3.47.

After turning off the power, C106 slowly fell from +3.47 to +2.37, THEN ROSE AGAIN TO +4.25, slowly fell to +3.33, Then Rose Again To +4.17 before falling off to +0v.


So, power up went like this:
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Power down went like this:
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What could be wrong with my board?
 

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the vias on the bottle caps are really bad about either coming out, or not making good connection from top to bottom. Check for voltage drop between the 3 leads of the bottle cap on the 5v, and the other end of the trace. Chances are, one of them isn't making good connection. The easy solution is to rerun that trace with a piece of 18 gauge wire.
 
I've been testing continuity as I go, but I ran some traces to make sure that it wasn't an issue. (Pic1) I wasn't sure how to safely check for voltage drop .

On power up, it peaked at +4.46, then fluttered down to +3.49.
While powering down, it went from 3.49 -> 1.69 ->back up to 3.93 -> 0.

This is crazy. Did I run these jumpers like what you were suggesting?


the vias on the bottle caps are really bad about either coming out, or not making good connection from top to bottom. Check for voltage drop between the 3 leads of the bottle cap on the 5v, and the other end of the trace. Chances are, one of them isn't making good connection. The easy solution is to rerun that trace with a piece of 18 gauge wire.
 

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