modessitt
Volunteer: Encyclopedia Submission Moderator
I've been messing with this today, and am getting nowhere. The sounds play, but there is a loud hum in the background.
I have already changed all the electrolytic caps on the sound board, as well as the 5 on the back board. When I touch the 104 mylar cap near the amp, the hum gets a lot louder. I replaced that 104 cap, as well as the 5 closest to it and near the same circuit. No change. I swapped out the amp with another I had. No change. I checked the resistors in that circuit and they are good (admittedly one should be 40k-ohm and is reading 47k-ohm, but I doubt that difference is my issue). I followed that line where I touched the cap to a LM3900N, but replacing that didn't help either.
What's my next step? I'm not finding a very good schematic for this, so I don't know whether getting an audio probe in there is going to help me much if I can't trace the inputs and outputs properly.
The game came to me with no sound (speaker unplugged - most likely due to the hum) and hooking it up gave me the hum. I replaced the power supply with a known good one, but that didn't help. Added a jumper from sound board ground to power supply ground - that didn't help.
Turning the volume up and down on the board at the main pot makes the hum a little louder or softer, but the regular sounds get loud or soft at a quicker rate. The hum is there even with the sound all the way down. Adjusting the seven individual pots (for each type of sound?) doesn't affect the hum at all.
Anyone got any bright ideas?
I have already changed all the electrolytic caps on the sound board, as well as the 5 on the back board. When I touch the 104 mylar cap near the amp, the hum gets a lot louder. I replaced that 104 cap, as well as the 5 closest to it and near the same circuit. No change. I swapped out the amp with another I had. No change. I checked the resistors in that circuit and they are good (admittedly one should be 40k-ohm and is reading 47k-ohm, but I doubt that difference is my issue). I followed that line where I touched the cap to a LM3900N, but replacing that didn't help either.
What's my next step? I'm not finding a very good schematic for this, so I don't know whether getting an audio probe in there is going to help me much if I can't trace the inputs and outputs properly.
The game came to me with no sound (speaker unplugged - most likely due to the hum) and hooking it up gave me the hum. I replaced the power supply with a known good one, but that didn't help. Added a jumper from sound board ground to power supply ground - that didn't help.
Turning the volume up and down on the board at the main pot makes the hum a little louder or softer, but the regular sounds get loud or soft at a quicker rate. The hum is there even with the sound all the way down. Adjusting the seven individual pots (for each type of sound?) doesn't affect the hum at all.
Anyone got any bright ideas?