Sea wolf drags +5v down to 2.5v

mrsodapop

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I have a sea wolf that I was told worked a few years ago. I disconnected main PCB wiring to test PS PCB. All voltages checked out great. Checked to make sure all motherboard connectors were clean, plugged everything back in and powered on. All I got was a lot of missile/explosion sounds, no video. Checked voltages, all were good, expect for the +5vdc, it was now at 1.5vdc. Tried to adjust on the PS PCB with no luck. I thought the PS may have problems, so I installed a switching PS for the +5,-5,and 12v(I had planned on doing this anyway). After powering on , same thing. All voltages check out, except for +5 it is now +2.5vdc. If I unplug the mother/daughter boards, All voltages check out fine. Anybody have an idea where to look next??
Thanks for any help
Aaron
 
Your problem is a simple one, believe it or not its the wiring between the PSU and the board, you need thicker wires. Either thicker wires or multiple runs of the thin stuff. Older and bigger boards tend to need more current than more modern ones which is why you may not have any problem with other boards. The board is trying to pull more current then the wires can deliver so the volts sag badly. You will probably be able to feel your existing wires and the edge connector get warm too. Its a common problem, especially with the pissy prewired harnesses you can buy on ebay - they use the thinnest wire imaginable, which is OK for control lines but not for ampy power.

I know this sounds very implausible, but add more copper and be amazed.
 
I have to admit I was very skeptical, But I was pleasantly surprised. You were right, I soldiered a larger gauge wire to +5 and ground to main PCB, and no more drag. I now have a rock solid +5.2vdc(unfortunately game is still dead, but that seems to be another problem).
Thanks very much for the info!!
 
Excellant, this is why my test bench has insanely thick wires for all power and ground cables to the JAMMA adaptor, I think they are rated at 25 amp, the wire is actually intended for car batteries but I got so sick of having even the slightest volt sag when working on bootleg boards that I went silly and decided I never wanted to face the probelm again.
 
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