CoinOpSpace.com - Classic Arcade Game Forum
Classic Arcade, Pinball and Console Collecting Gaming Community
SOLUTION: Pac-Man 5A Fuses Blow
4/4/2009 - Update: Problem Solved! After talking through my troubleshooting with my dad, I remembered something. Just after the fuses blew, I felt around the game board for overheated components. The Z80 Sync Bus Controller was the culprit. After inspecting the board and the orientation of the surrounding chips and the other daughter board, I came to the conclusion that this board was installed upside down!
I just picked up some brand new fuse holders and fuses to install in my Pac-Man project. I fired the game up, and I noticed the two 5 amp fuses glowing bright orange. Sure enough, they were bad when I pulled them.
Anyone know what would cause these 5 amp fuses to blow?
P.S. If you are interested here is my CoinOpSpace blog post about my recent pickup.
I just picked up some brand new fuse holders and fuses to install in my Pac-Man project. I fired the game up, and I noticed the two 5 amp fuses glowing bright orange. Sure enough, they were bad when I pulled them.
Anyone know what would cause these 5 amp fuses to blow?
P.S. If you are interested here is my CoinOpSpace blog post about my recent pickup.
Replies to This Discussion
-
Permalink Reply by Shane on -
So, these were already blown when you started the machine up ? What happens when you replaced them? did they blow as well ? I would take a volt/ohm meter and check the voltage before it passes through the fuse and see what voltage is coming out of the transformer. Maybe you got too much !
-
Permalink Reply by Brian Hanifin on -
Shane,
The fuses and the fuse block were brand new. I wondered if it might be a high voltage issue. I guess I need to look at the manual. ;-)
-
Permalink Reply by Shane on
-
are these the two fuses off to the left near the edge of the board or the 4 fuses off to the right of the transformer ?
-
Permalink Reply by Brian Hanifin on
-
Shane,
There are on the right. The bottom two from that group of four.
-
Permalink Reply by Shane on
-
Brian Hanifin said:Shane,
There are on the right. The bottom two from that group of four.
Ok, i think the two bottom ones are both 7 volts. If its a MT-80 transformer like in my Galaxian should look like
7-0-7-0-12-0-12... I think the wires coming of the 0's go to a small filter board or jumper board. Im not sure what that is but check the voltage coming off those 7 volt leads on the transformer.
-
Permalink Reply by Brian Hanifin on
-
I tried to clip my negative lead to what I thought to be a ground tie in on the metal monitor chaise mount. But, I didn't get a reading on my meter. As an experiment I tried a couple of lugs of a transformer. This may be the incorrect way to do it... I just wasn't sure where to find negative test point.
Assuming my negative test point was OK... the readings at the incoming side of the fuses are: 11.9, 12.1, 7.0, 7.1. These sound like good voltages to me.
Now for the weird readings. With the 7v fuses removed (they were the ones that blew), the outgoing side gave me readings of 1.3 and 1.0!?! Shouldn't those read 0?!? As in there should be no voltage here because the fuse meant to carry the voltage is not connected?
As a test I removed one of the 12v fuses and tested the outgoing side, which gave me 0 volts, as I expected. :-/
Is the voltage coming from the "wrong side" blowing the fuses? Or am I tying the negative lead on my meter into the wrong spot giving me false readings?
-
Permalink Reply by Shane on
-
Brian Hanifin said:I tried to clip my negative lead to what I thought to be a ground tie in on the metal monitor chaise mount. But, I didn't get a reading on my meter. As an experiment I tried a couple of lugs of a transformer. This may be the incorrect way to do it... I just wasn't sure where to find negative test point.
Assuming my negative test point was OK... the readings at the incoming side of the fuses are: 11.9, 12.1, 7.0, 7.1. These sound like good voltages to me.
Now for the weird readings. With the 7v fuses removed (they were the ones that blew), the outgoing side gave me readings of 1.3 and 1.0!?! Shouldn't those read 0?!? As in there should be no voltage here because the fuse meant to carry the voltage is not connected?
As a test I removed one of the 12v fuses and tested the outgoing side, which gave me 0 volts, as I expected. :-/
Is the voltage coming from the "wrong side" blowing the fuses? Or am I tying the negative lead on my meter into the wrong spot giving me false readings?
Hey Brian, I put some pics in here that might help. Now there are probably some differences in transformer voltages between Pac Man and my Galaxian. But i think the setup orientation is similar. You should be able to use the transformer lugs as a suitable ground for your black test lead. And set your volt/ohms meter to 200v AC scale. I could be wrong but ive been checking the voltage on the right side of the transformer which the 4 fuses are closest too. I believe that is the out side of the transformer and supplys the voltage to the main harness connector. Ive taken close up pictures as an example of the out side voltage power. When you test them, you should get the values that are printed on the transformer. On the in side of the transformer should be your incoming AC voltage and by the time it gets to the out side the power should be reduced to smaller values. This is the transformers job to reduce those values to a managed level so it wont harm the PCB. Now getting back to the out voltages, Those voltage values should also be the same even after they pass through the fuse. In the picture i show here you'll see how my test leads are and notice i have only like .1 volt which is telling me that my transformer is not doing its job by outputting the proper voltage value. In fact across all the leads on the transformer are not putting out the proper voltages so iam having to replace my transformer. Hope the pics help.
-
Permalink Reply by Brian Hanifin on
-
Thanks for the tips Shane! The MT-80 Transformer has the correct output voltages. However, I now realize that one of the two 115v posts on the upper transformer are dead! I guess I will have to replace that one.
So, if my output voltages are not too high, why are the fuses blowing? Could it be the phantom voltage from the outgoing side of the fuses?
Should I replace the dead transformer before I troubleshoot these blowing fuses further?
-
Permalink Reply by Brian Hanifin on
-
OK, after some reading I think this is an Isolation Transformer. The brown wire goes to one of the two 115v fuses. Should I buy a new isolation transformer? If so, do you think I can pick one up at a local electronics supply shop?
-
Permalink Reply by Shane on
-
Brian Hanifin said:OK, after some reading I think this is an Isolation Transformer. The brown wire goes to one of the two 115v fuses. Should I buy a new isolation transformer? If so, do you think I can pick one up at a local electronics supply shop?
Yeah, kinda looks like you got a dead bridge there on the 115 side with zero voltage. Thats probably part of the problem if not the problem. I would replace that but i dont think your find one of those at your local radio shack. Start looking on ebay for one with the same midway part number. Or PM Alan, he might have one. I know he had the MT-80's but i had already bought one off ebay.
-
Permalink Reply by Brian Hanifin on
-
I sent an Email to Bob Roberts inquiring about a replacement for my bad Isolation Transformer. His response:
Xformers don't go bad & this one is for operating voltages, anyway.
So, I traced the wires and found the brown and orange wire I assumed should be putting out 115v is actually the return from the monitor. The monitor turns on, so shouldn't I see voltage return from the monitor? I should get a voltage reading at the return fuse... right?
"DUH" Moment: now that I realize the top lugs are the outgoing and the return for the monitor... when I test directly across those two lugs, instead of starting the negative at ground I get 119v! Ha! I've been chasing my tail. At least now I can go to bed! ;-) I'll get back to trying to figure out the 5v fuses blowing tomorrow.
About
© 2010 Created by Jeff Rothe.
Powered by 
.
