Short on a Pacman PCB

[wishiwas]

I have a PacMan board that has a short somewhere. The voltage at Q6, IR1 and the caps are too low and one of the ground wires going to the header connector gets hot.
Is there a common component to check? I looked at all the caps close to the rails and they all look good.
I just unsocketed all the socketed chips. When I ring out a socket (top pin on right / bottom pin on left) every one of them rings. My working board doesn't
I have a multimeter, probe and Oscilloscope, but I dare not apply power to the board again until I fix the issue. The power wires going to my switching power supply got hot!

 

[sukhbir]

Has this pacman pcb ever worked?are you using a switch mode power supply or AC transformer to power your pcb?
if you are using a switch mode power supply and your pcb has a short the power supply goes into protect mode and should not pump high amps into your pcb.

 

[wishiwas]

Has this pacman pcb ever worked?are you using a switch mode power supply or AC transformer to power your pcb?
if you are using a switch mode power supply and your pcb has a short the power supply goes into protect mode and should not pump high amps into your pcb.

I am using a DC switching power supply. I works just fine on other "working" boards. There has to be a short on this board somewhere because the wires heat up when I ring out certain areas vs the working board, it rings when it shouldn't. I replaced the TIP31C and the 78GU1C last night. No change.

 

[qjuk]

Are you working on an original Namco/Midway board or a bootleg?

When you say “ring out” are you on about a continuity check using a DMM (digital multi-meter)?

Bad capacitors can cause shorts (even if they physically look fine).

 

[Hexen]

I have a PacMan board that has a short somewhere. The voltage at Q6, IR1 and the caps are too low and one of the ground wires going to the header connector gets hot.
Is there a common component to check? I looked at all the caps close to the rails and they all look good.
I just unsocketed all the socketed chips. When I ring out a socket (top pin on right / bottom pin on left) every one of them rings. My working board doesn't
I have a multimeter, probe and Oscilloscope, but I dare not apply power to the board again until I fix the issue. The power wires going to my switching power supply got hot!

Any Tantalums about? Damaged disc ceramics? I would suspect a Tantalum. Wires getting hot is better than ICs, but do any of the components get hot? I guess it's the 5V line? Can you post a schematic, there are lots of pacman boards.

What do you mean by 'ring out'?

 

[Lurch666]

Check underneath the PCB to see if any pins of the ICs are bent and touching something they shouldn't.

 

[Hexen]

Check underneath the PCB to see if any pins of the ICs are bent and touching something they shouldn't.

It's possible, but I bet 5p it's a Tantalum. I'm shaking my fist at the sky and screaming the T word, à la Khan.

 

[wishiwas]

Are you working on an original Namco/Midway board or a bootleg?

When you say “ring out” are you on about a continuity check using a DMM (digital multi-meter)?

Bad capacitors can cause shorts (even if they physically look fine).

Yes, continuity using dmm. On a working board, it will ring for a second or so until the juice of the cap is exhausted then stop. This board it just stays ringing. I moved onto a Galaga issue but I am coming back to this board today. I will try clipping one side of some caps.