Got a very pretty Hulk in our showroom. It was up and sort of running for a while, but then I used its power supply to fix someone else's Sinbad. I ordered the parts kit from Big Daddy, and replaced pretty much everything that wasn't a resistor. One of the diodes he included went bad, but hey, that happens. I've got it so when I just have A2-J1 plugged in it reads a beautiful 5.0v on the correct pins of A2-J2. The problem is that as soon as I plug in A1-J1, that reading drops to -.5v. That's clearly not correct. But it happens when I plug in ANY of the MPU boards I have. I suppose all 3 could be bad in exactly the same way, but I'm very skeptical. What's going on? Why is the 5v dragged so far down?

1 month later

#2 8 years ago

HEN

johnnyatari

Hendrickson Electronics

Oskaloosa, IA

9y 24,150 29 2

Check SCR101 it's a S107Y1 - replacement part (NTE5452) - over voltage protection.
They get very hot when bad and the plating usually looks bumpy (if they over heat) when they fail.
The other thing is the potentiometer for the +5V. Check it with an Ohm meter while turning (out of game) and see if there are any dead spots. You can clean the pots with alcohol or use DeoxIT (contact enhancer).
There are two SCR's on the power supply (SCR101 & SCR201) the first is for +5VDC and the latter is for -12VDC.

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