I'm working on a System 1 that I bought not-working. I've got the power supply rebuilt and working with proper voltages, but can't figure out a fuse blowing problem on the 69v circuit. I've narrowed things down a bit - for it to blow, which it will continually, I have to have the following connections
1. power supply (A2J3) to displays
2. power supply(A2J2) to CPU Board (A1J1)
3. A1J3 plugged in connecting CPU board and displays (the lower of the connections to the displays)

All my displays are unplugged, as is the connections between the driver board and the CPU board. I've examined the wiring, the connectors, and the wiring jumper bakelite boards on the light board for shorts, but none found. I've also swapped CPU boards, but same result. Note: Neither CPU is known to be fully working, I just haven't gotten that far.

I'm lost at this point. Anything obvious to check? In the meantime I was going to try and verify the pinning of the connectors used, in the case that someone repined them wrong before I got the project.

Thanks in advance,
BTW

Oh yes, all over that. Anything in particular you think I might be missing?

No. I have to have those that I listed plugged in for the fuse to blow.

Thanks for the help-

Yes, That is what I'm saying. Correct.

Correct. I've been connecting with the power off - SINCE I read warnings about that. Not sure though what might have been messed up by doing that or if it could be part of the problem.

I checked the 60v, but not the 42v. It wasn't completely short to ground, I want to say there was about ~4k ohm resistance. Sound ok?
Will check the 42 tomorrow.

I verified the ground and power connections and believe they are correct.

Yes- All the displays are disconnected. I tried to find the minimum combination of connections.

Torch

No short from 42v, measured from power supply to end of 42v string at status display - about 10k ohms.

Voltages rechecked, all seem great. Also rechecked plug configuration - All of those 3 must be plugged in to blow the fuse, and if they are, the fuse will blow within seconds.

Any suggestions welcome. I'm not too far away from starting to just buy new boards - I just wish that'd guarantee a fix! It seems though the problem must be related to a short in the display wiring... I do admit that I don't know what the appropriate resistance is between 60v and ground in that harness. Is ~10k normal or should it be OL?

Yes, pins look good.

Voltage wise? I get 60v & 42.8v.

Here is something I just noticed - the 5v & ground on the CPU board has ~220 ohm. Wondering if I damaged boards by plugging in connectors with the power on before I saw the warnings.

Fixed. The Q2 was shorting to the back board in the powersupply. Not sure why that didn't cause an immediate fuse blow, but that took care of it. Now to troubleshoot displays - I get power to them but nothing there. I have plenty of back up boards so I don't mind swapping some chips but will try to find the actual issue first so I don't have to shotgun.

Thanks pdman. I can't start a game either.

While I was troubleshooting I realized that I had not more 5v - it was down to 2.3ish. I had a solid 5v,4v,8v yesterday (and maybe earlier today), so I don't know what happened, but I've got a hunch that the big power transistor is flakey since this happened a day or two ago and reflowing the solder helped, but not this time. Since testing anything without a good power supply is worthless, I am going to take a break from this game and wait for the weekend when I can get my hands on a known good pascal all-in-one. That way I'll know if the displays and everything else is good.

In the meantime, I might replace that Q1 with a different one just to see if I can get that power supply back on its feet.

Resolving this thread: I brought out the scattergun and just bought a GPE & Ni-Wumph CPU board.

Sorry - the no displays comment was old. I'll edit that out. I ended up rebuilding the display boards as I had 2 or 3 bad 6118 chips and went ahead and replaced the capacitors. The CPU board didn't ever boot up and I just cried uncle and bought another.