I was having sound issues on my Monster Bash, it sounded a bit like it was muffled or underwater. So I first looked on pinwiki and got some good advice there that maybe the amp chip had failed. And someone else told me that capacitors probably needed replaced.
Tested fuses, all good. Scratched my head. Looked for those amp things and identified two transistor-looking thingies with 5 legs and huge heat sinks attached, on the AV board. Then I called Phil from Pinball Heaven for advice.
Good old Phil. First he had me let him listen, and he said it wasn't the caps but that the amp was indeed probably failing. Then he had me remove first the cabinet and then the backbox connectors and we determined that the cabinet speaker sound was off. So he had me measure the speaker resistance, all good at 4 ohms, but I tried a new speaker just in case. No improvement, so probably amp U6, not sure why no backbox sound though.
Then while I had him on the phone, I saw a puff of smoke and now I had no sound at all. Tested and found that both the 2.5A fuses had gone. Put two new ones in and watched them flash pop immediately. Then like a dick I took one of the fuses out using a screwdriver with the game still on, and immediately saw a new puff of smoke from the second amp as I accidentally shorted across the fuse, smoke from the one for the backbox speakers, U5. So they were now both gone and I needed new ones. Ordered some.
Phil told me that whatever had caused U6 to be on its last legs now needed to be found, or it'd just happen again, so I measured resistance at the connectors - 4.5 ohm at the one for the cabinet speaker, but only 0.5 for the backbox ones. Huh? So he made me unsolder each backbox speaker in turn and remeasure resistance at each speaker and at the connector, and we identified that one speaker, the far one, was fine at the lugs but less than an ohm when I measured from the wires going to them. So he told me to trace the wires and said a wire was probably caught behind my colour DMD.
Lo and behold I found this, where the speaker wire was trapped behind the metal frame of my colour DMD
So I replaced that wiring and now had 4ohms at each speaker connector. What had happened was that the speaker wire had shorted to earth via the DMD frame, the lower resistance had caused a current surge and stressed both those amps, one of which failed before my eyes in the first puff of smoke, the second one also on its last legs and dying when I stupidly allowed more than 2.5A through it.
The replacement amps, called TDA2030 arrived (a few quid off eBay) and I just soldered them in. All perfect sound now
Take home messages-
1) a trapped wire can cause a short, low resistance means more current and trouble
2) never take out a fuse with a metal object with the power on, or you basically fry whatever is downstream.
Tested fuses, all good. Scratched my head. Looked for those amp things and identified two transistor-looking thingies with 5 legs and huge heat sinks attached, on the AV board. Then I called Phil from Pinball Heaven for advice.
Good old Phil. First he had me let him listen, and he said it wasn't the caps but that the amp was indeed probably failing. Then he had me remove first the cabinet and then the backbox connectors and we determined that the cabinet speaker sound was off. So he had me measure the speaker resistance, all good at 4 ohms, but I tried a new speaker just in case. No improvement, so probably amp U6, not sure why no backbox sound though.
Then while I had him on the phone, I saw a puff of smoke and now I had no sound at all. Tested and found that both the 2.5A fuses had gone. Put two new ones in and watched them flash pop immediately. Then like a dick I took one of the fuses out using a screwdriver with the game still on, and immediately saw a new puff of smoke from the second amp as I accidentally shorted across the fuse, smoke from the one for the backbox speakers, U5. So they were now both gone and I needed new ones. Ordered some.
Phil told me that whatever had caused U6 to be on its last legs now needed to be found, or it'd just happen again, so I measured resistance at the connectors - 4.5 ohm at the one for the cabinet speaker, but only 0.5 for the backbox ones. Huh? So he made me unsolder each backbox speaker in turn and remeasure resistance at each speaker and at the connector, and we identified that one speaker, the far one, was fine at the lugs but less than an ohm when I measured from the wires going to them. So he told me to trace the wires and said a wire was probably caught behind my colour DMD.
Lo and behold I found this, where the speaker wire was trapped behind the metal frame of my colour DMD
So I replaced that wiring and now had 4ohms at each speaker connector. What had happened was that the speaker wire had shorted to earth via the DMD frame, the lower resistance had caused a current surge and stressed both those amps, one of which failed before my eyes in the first puff of smoke, the second one also on its last legs and dying when I stupidly allowed more than 2.5A through it.
The replacement amps, called TDA2030 arrived (a few quid off eBay) and I just soldered them in. All perfect sound now
Take home messages-
1) a trapped wire can cause a short, low resistance means more current and trouble
2) never take out a fuse with a metal object with the power on, or you basically fry whatever is downstream.
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