Lots of great info here. I was stumped for a bit with no sound and good wiring harness from sound board to MPU until I read about leaving the 2 left most pins on the MPU side not connected. (Lectronamo)

Only issue now I have is a mid range pitched hum coming out of the speaker at all times. It goes up and down with loudness with volume just as the regular sounds do when turning the volume knob on the speaker.

Anyone else run into this noisy background midrange pitch hum?

Thanks,
Dave

Tried changing switch #23 both ways. No difference. I'm thinking it may be a compromised BR2 as that's what was causing a hum in my Stern Cheetah a while back.

I replaced the electrolytic caps in the sound board except for the bi-polar ones. >>> No change.

Video here of the sound:

Thanks for the info Andrew. Looks like adjusting R2 has no effect on the sounds and yes I now notice that through sound test there are 1 possibly 2 pitches missing. I took the board out and tested the ohms on the variable R2 and it does adjust. So looks like it could be either of those 2 chips that you mentioned. Adjusting the each of those pots with game on , the speaker gives out sounds like tuning in am radio (sweeping background pitches noise/hum).

tp 2 = 2.53v
tp 3 = 5v
tp 5 = 2.53V

Great plains carries 74F08 but not the 7408 as it looks like it has been obsoleted.

Looks like this would be a good substitute as it has a 20ma rating and the orig has 16ma rating?

Wow! Some more great info on this sound board! This should be done with board set to electronic sounds not chime type sounds yes?

Very good. Just tuned the ones that worked and Andrew is right. Missing the 10 point sound just a tap sound for it when hitting a 10 point switch.

Although, when I first powered it on today to tune it. The 10 point switch sound actually worked for a few switch presses. Then it went back to just tap sound.

2.38v pin 3 u8
2.38v pin 3 u9
2.42v pin 11 u9

Just checked and same tapping sound for 10,000 point sound effect

Did this by dropping the upper left targets a few times. Special set to give 100K in ten 10K increments

Yes click sound.

Will check pin 5 and pin 1 on U8 next and the chime setting for difference.

Standby. =)

when set to chimes, I am getting 10 point chime sound from 10 point switch. Still no 10K sounds at all though. Not even a click with it set to chimes for this test.

U8 pin1 = 5v
U8 pin5 = .04v

Just set it back to electronic sounds and back to 10 point and 10K point click sound.

Another weird abnormality with this game....

The knocker is mounted just below the sound board. And when it knocks, most time the game reboots. Changed out the diode on the coil as I thought if compromised it could cause a reboot. No change.

So I "solved" this by mounting the knocker below the Sol Driver board instead. No more reboots when knocker is activated.

Even tried to duplicate it with using a light hammer on the area where the knocker was located, no reboots.

With game on for a few minutes, they both feel pretty room temp to touch.

Thanks Quench for all the info. Just ordered the chips. Will report back once replaced.

Thanks for all your help Quench and Andrew!

Still waiting for my GPE sound board parts to come in to fix the missing 10's chime sound issue.

So in the mean time, started work on getting a Bally -17 MPU rebuilt for the game and take my test Altek back out of the game.
After replacing all sockets (except for U9, U11,U10) and ALL connector pins on this MPU board, noticed I had no 1000's digit and no 10's in all displays. Found the issue to be I left 2 pins unsoldered at J1 on MPU board. Lightly soldered those in properly and now displays all work well but now erratic CPU noise upon bootup and during game. Replaced all 40 pin sockets as thought perhaps U11 or U9 bad sockets to blame for it co-incedently. No change after socket replacement and even swapped in new U11, U10 and U9 chips.
Lastly unsoldered J1 pin strip as this is the last thing I did before encountering this sound issue, inspected for bridging etc (no issues found) soldered new J1 pin strip in again. Same issue.

Checked game with an Alltek installed and no sound issue. Problem resides on the -17 MPU.

Video here of the erratic sound warbling from the MPU:

I think your Stern MPU 100 game and mine are haunted by the same ET trying to phone home.