I have an old Williams solid state pinball machine that I have been working on for sometime. I recently solved some issues with the CPU board and finally had a chance to get the driver board in. My question is with regard to the attached schematic.

When I hook up only jumpers 2J4 and 2J6 (boxed out in red in the schem), an 18V DC supply, I measure ~4A from this supply. It seemed high to me for it not actually driving any lamps (none in place) and didn't want to damage anything? All of the 5V logic is powered as well in the schematic but off of a different supply.

All comments appreciated.

 

Hi Dalaran,
Keep in mind that the machine is OLD.
Aluminum electrolytic capacitors have a shelf life; they "lose" their dielectric (the stuff that insulates the internal plates) when they haven't been used for a while; and if they are powered up when their dielectric is down, they will act like (and be) a dead short - and they will be damaged in the process. Also, the electrolyte can leak out or dry out after a number of years. If you see odd patches on the PCB that look white, it could be leaking electrolyte.

The schematic you posted is fuzzy, and I can't see if there are any capacitors in the circuit. However, you should be suspicious of them if there are any. I'm talking cylindrical capacitors, not flat ceramic caps.

Beyond that,

 

Hi Sgt,

Thanks for the reply. I have had to replace a number of electrolytic caps on the power supply board as you mentioned, they get old. However there are none of these on the driver board here in question.

That being said, does this 4A current draw sound reasonable based on the number/type of components it is powering?

Again thanks for the help.

 

Sorry, I can't tell by that schematic. I can't read it. My eyes aren't that great anymore.

 

Fair enough, I appreciate your time. I will try to post a blown up version of atleast the components in question when I get home.

Cheers.