(Topic ID: 110285)

Tech Help: BTTF - No sound and one stuck on lamp. (updated)

By DropTarget

7 years ago

Topic Heartbeat

Topic Stats

  • 11 posts
  • 2 Pinsiders participating
  • Latest reply 7 years ago by DropTarget
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#1 7 years ago

Hi All,

My Back to the Future is sick.

I don't know what happened, but (making a long story short) something caused the PIA chip on my MPU to fry. That was repaired, and now the game boots up and plays. However, there are no playfield lights, sound or left sling coil, just GI lighting. Obviously something spiked the game and took out a bunch of stuff. BTW, I have a new Rottendog power supply now.

Any thoughts?


#3 7 years ago
Quoted from bimm25i:

check the 2 fuses on the left of the backbox directly above the giant capacitor, If you replace the fuse and it blows again you probably have to replace one of the bridge rectifiers screwed to the cabinet in that same location. the youtube link below gives instructions for testing the rectifiers

Thanks Bimm25i,

The bottom fuse, a;though looked good was blown. The one in the game was rated at 32a, I replaced it with a 20a fuse, and the lights came back. Now the issues are: 1) no sound at all, not a hum, not a click....nada. 2) The left sling kicker still inop and 3) The "Light Extra Ball lamp is always lit.

#4 7 years ago

Also, I just noticed that the left kicker works in test mode, as well as the "light Extra Ball" lamp is obviously out during the individual lamp test, but does light when it is tested.

Transistors?? I don't have the matrix.

#6 7 years ago


I think I read voltage instead of amperage on the old fuse.

#7 7 years ago

Do you know if REG1 is the same as VR1 on the soundboard?

It's the only voltage regulator that I see. It's output is 8.91V

Thanks again

#8 7 years ago

#9 7 years ago
Quoted from bimm25i:

wow, I think I have 8A fuses in both those slots.

8A is correct

#10 7 years ago

Left kicker fixed, broken wire, replaced VR1, still reads almost 9V at the regulator, but -5V at C49

#11 7 years ago

Stuck light is fixed.....Bad diode and a jumper that shouldn't have been there was removed.

Sound problem diagnosed, a bad 12V power regulator on my new power supply board. Replacement board on the way....

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