Don't know if rebuilding the power board would help as I just installed a brand new power supply board from pinballpcb and I still have a hum. Could it be an issue with your speech/sound board? In my experience there always seems to be an annoying hum with these older pins.

Check your voltages to start.

Any update on your voltages?

LIONMAN

That reminds me... be right back.

I dealt with a bad amp in a Big Guns that made static recently. Is it ground hum or just other staticy yuck noise.

Sounds good. Were you able to test the voltages on the board?

Thanks,
--Scott

I would check all the voltages on the power supply. Your friend that recommended yo change the capacitors on the PS is probably on the right track. Let me know if you have questions and I can compare on my Pinbot if needed.

Probably a dumb question but when you checked the grounds did you check that all the mounting screws on the mpu board were present and tight? My system 9 hummed horribly until I replaced 2 missing screws and made sure they were snug.

This is normal. The diagnostics LED should be blinking continuously. If it's locked on solid or off, that would be a problem.

Also usually a normal indication. If it's sequential, and operating various kickout holes, the game is attempting to remove balls for initialization. Sometimes a bad switch or missing ball can cause this process to repeat several times. If a coils gets locked on and stay on, and that's totally different - usually resulting in burned coils and/or transistors.

This might be approaching a more advanced skill set in troubleshooting, and often requiring an oscilloscope to track down where the distortion is coming from.

Agreed. I know a buddy of mine is having the same issue with his F-14. I believe this is the same sound board.

I will reach out to him to see if he solved this.

F-14's issue is a design/programming error in the music section. All f14s are affected, and it cannot be fixed without reprogramming the sound board.

This guy's problem is unrelated.

Since he's getting distortion in both music and speech, fault has to be after they've gone through the mixing section. That eliminates a lot. Most often bad actor is the volume pot (and especially the wiring to/from it), then u1 (tda2002 if memory serves) and the circuitry around it (caps). Outside chance that it's the 1451 right in the mixing section, but those rarely go bad compared to u1.

Scope would show distortion. If I had to go in blind I'd go at the volume pot, idc connector, and its wire. SO many problems there, and easy and cheap to swap if need be.

No change in recommendations.

Interesting that re-flowing all the pins made a big difference here. Were there any with noticeable cold solder joints?

Did you reflow solder over the ground areas where the screws attach?

I was curious because I was wondering if that is what solved the issue. Always good to have a log here of what the solution was for others to use as reference. I usually sand down solder mask and solder over those areas to ensure good ground connections as they're usually nicely oxidized since they were never tinned.

Interested to know what you find. My Pin*Bot had a similar ground hum when I first got it home and no sound. After a few days of sitting it just started working. Only problem left was the speech goes out after 15 to 20 minutes and slowly becomes distorted as it fades. If you cut power off and back on speech comes back for another 15 to 20.

Also that hum from your video is in my High Speed when it first boots, but goes away once a game starts.

There is a lot of other components that can be the culprit, so I would not be surprised if it wasn't solved after replacing the caps a second time around. ICs go bad. Resistors go bad. Signals can become offset, causing a change in the noise floor, etc.. If you were able to examine it with an ocilloscope you have a much better chance of being able track this down. If you don't have advanced audio troubleshooting skills or tools, you could be changing parts for a long time and get nowhere. Have you at least isolated the problem to one board? (example: you tried with another sound board or power supply board - and that solved the problem)