Ms. Pacman Blowing 1 AFB Fuse

MunsonRoyE

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Hi all! I've been working on getting the Ms. Pacman up and running and I am having an issue with the final 1 AFB fuse blowing on the 5-5-1-1 fuse board. When I turn on the machine I can see the fuse glowing and I gets really hot before it finally pops after a few minutes. Everything works fine while the fuse is active. Once it goes the game still plays, but the monitor gets a wave in it.

The PCB has some burnt edges on it so I thought that might be it. I installed a Pacmend kit and that didn't help.

I have 2 working daugher boards and it still blows with each one.

If I unplug the monitor it still blows.

If I unplug connector from the board the fuse is fine, which leads me to believe there maybe something wrong with the board.

Could this be an issue with the caps on the board or is it more of a chip issue?
 
Do you lose sound when it blows?

Try unplugging your coin door, and if that doesn't work, your marquee light. Those fuses are on the 12v line. You could also check the rectifying diodes on the board where it converts it to DC for your sound section...

Also, if you look at the Ms. Pac-Man wiring diagram in the manual, it calls for only one 1A fuse, three 2A fuses, and two 5A fuses.

I know that Bob Roberts says 5-5-1-1. Just telling you what the wiring diagram says...
 
OK, I checked it out and the fuse that is actually blowing according to the diagram is the 7v 5a fuse with the orange wires.

I made sure all the fuses were correct. I unplugged the coin door and the speaker and the fuse still has issues. Without the fuse in, the sound is still present.
 
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Okay, that fuse is your main 5v line to make your board run. You have two diodes on your board that rectify the 7vac to 5vdc for your game board. I'd check them to make sure they're okay, and that your getting +5 on the ROM side of the diodes, and that you're not getting much AC bleedthru...
 
Well, you do it with the power off first. Set your meter to diode test, then put the black lead on the banded side and the red lead on the other side. You should get a reading between .400 and .700

Next, with the power on, set your meter to DC-20, then stick your black lead on a ground point somewhere (such as the negative leg of C7) and the red lead on the positive leg of C7. You should have a DC voltage reading of about +5 volts, give or take. Next, you can try to get the same reading on AC-20 to see if you are getting any AC ripple through the diode.

You'll want to have your meter leads in position (alligator clips are excellent for this type of work if you don't have steady hands or spring-loaded test tips for your meter) when you power on so that you can get good readings before the fuse blows....
 
Alright, I'm thinking the fuse holder may be having issues. I switched both the 5a fuses and the power rating switched for the diodes. I replaced both fuses and now I am getting -7.9 for both of them. I am putting the red lead of the multimeter on the top of the diode and the black lead on the bottom. Is this correct?

I think I may go to Radioshack tomorrow and buy a new fuse holder.
 
Alright, I'm thinking the fuse holder may be having issues. I switched both the 5a fuses and the power rating switched for the diodes. I replaced both fuses and now I am getting -7.9 for both of them. I am putting the red lead of the multimeter on the top of the diode and the black lead on the bottom. Is this correct?

.

Not if the power is on, it's not. I explained how to test the diodes above with the power off, and what meter setting to use. If you look at the diode (or the picture on the board) you'll see one side has a stripe. That's the side that gets your black lead....
 
I just got home from work and checked the D8 and D7 diodes. I am only getting a 094 reading on them. Once the power is turned on I am getting a reading of 7.6 from the C7 cap.

Does this mean the diodes need replaced? If so, which ones do I get? Can they be purchased from Radioshack or do I have to order them from somewhere else?
 
You can try replacing them. The diode is a 1N4004. If they don't have them at a Radio Shack, you can try a Fry's Electronics if you have one (look for a NTE 116) or you can order some from www.mouser.com ...
 
I just purchased the 1N4004 diodes that you mentioned at Radioshack, but they look smaller and have a thinner wire than what are currently in my D8 and D7. These diodes match closer to what I currently have in D6.

Are these smaller diodes an acceptable replacement for the larger ones in D8 and D7?
 
I just purchased the 1N4004 diodes that you mentioned at Radioshack, but they look smaller and have a thinner wire than what are currently in my D8 and D7. These diodes match closer to what I currently have in D6.

Are these smaller diodes an acceptable replacement for the larger ones in D8 and D7?

D7 and D8 are A15 diodes....much more robust than those 1N4004's. Go back to Radio Shack and grab a couple 1N5400, or 1N5401...or 1N5402, or....you get the idea. Keep it in the 54XX series, but don't go too large...the legs might not fit through the thru-holes.

Edward
 
Fuse holder and diodes have been replaced. So far the fuses are holding up. Thanks for all the help everyone!

I checked the C7 cap and the and it's still coming up as 7.6 volts. Is this a problem or is it OK for the voltage to be in this range?
 
That is just fine.

C7 and C8 are on the outputs of those 2 diodes and are positioned in the circuit BEFORE the voltage regulation pieces.

RJ
 
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