Before replacing Q6, may I suggest that you have more to gain by diagnosing the mute issue first.

If you hold the reset line active on power-up as I mentioned in post #48, you will see a frozen reset state of the board.
The active low /reset line coming onto the sound board at connector J1 pin 25 goes to the active low CLR input pin 10 of the 74107 (U6) which should cause the 74107 pin 6 /Q output to be high. This will switch on transistor Q6 (there will probably be around 0.8 volts on the base pin of the transistor) and cause the transistors collector pin to pull down to near zero volts which is used at the amplifier chips (pin 1) to mute their audio inputs.

Some things to note:
The output pins of U3 and U4 (used to select/enable sounds) will be in an unknown state on power-up which could cause unwanted sounds to be selected/activated (i.e. you'd hear thumps/bleeps, etc). This is the reason for having the mute circuit on reset, to block these sounds.

After the reset line is released, the very beginning of program code writes data to U3 and U4 which clears their outputs to a known state of "low" to stop any sounds being selected/enabled *and* it also triggers U6 to stop muting the amplifiers, i.e. pin 6 of U6 will go low causing the Q6 transistor to switch off and release the mute signal at the amplifiers (you mentioned somewhere that the mute signal sits around 7 volts when the mute is disabled).
The mute signal on pin 1 of the amplifiers also has a 10uF capacitor (C42) which is used to slow down the release of the mute signal.

If your logic probe/multi-meter indicates logic/voltage states other than what I've mentioned, it can help pinpoint the fault.

Are you getting 10 volts supply to the MC3340 on pin 8? If yes, you might have an open circuit to the volume control in the cabinet.

Can you describe the "thump" you're getting on power-up? Your last video showed it play one of the game sound effects on power-up and I assumed this is what you're calling a thump. If the thump is a typical speaker pop, then it might be normal - sorry I don't have my game handy to verify. In which case you can probably ignore my last post. I may have gone into too much detail on the mute circuit..

With the machine OFF and your multi-meter set to resistance mode, hookup one meter lead to pin 2 of the MC3340 and the other meter lead to ground (TP4 on the sound board). When you adjust the volume control in the cabinet, the resistance reading should change. Does it? If not, you have an open circuit to the volume control or the volume control itself is bad. Use your meter in resistance mode to track down the open circuit.

The MC3340 is used to adjust the sound volume locally on the sound board. This avoids having to otherwise run audio signals to the remote cabinet volume control where it would be susceptible to pickup noise/interference through the wiring harness.
The wiring to the volume control in the cabinet simply adjusts a DC voltage on Pin 2 of the MC3340 which then internally attenuates the audio signal.

If the volume pot has no effect on resistance, there's an open circuit to the volume pot.

Good, so the connection from the MC3340 to the volume pot center swipe pin is ok.

So the volume pot itself is changing resistance, all that's left is the other wire on the pot that should connect to ground - sounds like it's the one that's open circuit. Do you measure zero ohms to ground on that other wire on the volume pot? It connects to ground back at the sound board.

Ok so there is an issue with the reset mute circuit, we'll revisit this one later.

Great stuff!
.

If you mean installing that 47k resistor, well it was totally bypassing the MC3340 and volume control. So that pin header was irrelevant to the sound circuit at that time.

Sure thing. When you're ready, come back and we'll follow up - the key points to it are in post #51.

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

When the volume is set to normal level for game sounds and the front door is closed, how noticeable is the hum?
Are all sounds otherwise playing ok?
Do you have the game configured for computer sounds or electronic chimes (switch 23 on the MPU board)?

Any chance of a video?

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:

When the game boots up, there should be more noises. I think one of your adjustable oscillating circuits is not working. Check solenoid / sound test too. The manua or someone else l hopefully gives you more info, but from memory sound / solenoid test is three different tones and two sweeping noises.

Check TP2, TP3 and TP5 the frequency / voltage will adjust with the nearby pot. 0v or 5v at these TP would 100% indicate an issue.... Should be somewhere in the middle. I think its possible for the pot to be bad or maladjusted out of a usable range to give this effect. Could be damaged damaged 4013 or 324 chips, but checking those TP voltages good place to start.

Side question. Aynone know the purpose of the V10 circuit on the sb100/sb300 boards? The 3340 shows it works up to 18v, so not sure why they drop down to 10v. Perhaps it clips or isolates from noise? There is a dedicated filter cap on the other side of the zener too.

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).

can you voltage check tp2, 3, 5? Doesnt matter if sound is playing.

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?

tp3 = 5v is the problem.

f08 should work fine for u7, but probably not your issue. I'd suspect u8 or u17

I see you're in great hands with Andrew and agree likely it's U17 and/or U8 causing the missing tones.

I was helping someone a while ago on PM who was having the same humming noise problem as you.
Turned out to be one of his LM324 op-amp chips (didn't tell me which one). So it's pointing to your U17 (LM324) as your failed part - get one or two spares just incase one of the other LM324 chips is causing the hum and also a replacement U8 as well. They are cheap.

BTW, to set the tones on your board so the melodies are in tune try this:
Open this online piano keyboard here:
https://web.archive.org/web/20191109111921/http://piano-player.info/

The following keys are the original high pitch tones the SB100 Rev-A board was tuned to - you might actually want to pitch them lower so they're less grating on the ear (Stern did this with later revision SB100 boards) but try to keep the notes scaled with another.

Keep hitting a 10 point score and adjust the R2 pot on the sound board until the frequency matches the white piano key 38 (note C6) [1047Hz]

Keep hitting a 100 point score and adjust the R13 pot on the sound board until the frequency matches the white piano key 36 (note A5) [880Hz]

Keep hitting a 1000 point score and adjust the R6 pot on the sound board until the frequency matches the white piano key 34 (note F5) [698Hz]

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

Yes, set it to electronic sounds when tuning the frequencies. When setting the game to electronic chimes the sound board basically adds the next harmonic to the base frequency of each tone which might make it a little trickier to match the frequency against.

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.

The 10 point sound frequency is also halved to generate the 10,000 points sound.

What voltages are you measuring on pin 3 of U8 and pin 3 and pin 11 of U9?

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

Hmm, I expected pin 3 of U8 to be wildly different from the others. What do you measure on pin 5 and pin 1 of U8?

If you set the game to chimes, do you get any 10 point sounds?
BTW when you say "tap" sound, do you mean a click sound?

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.

If 10 point scores generate a high pitch tone with the game set to chimes, it's all pointing to U8 as the faulty part. If you touch U8 with your finger, does it feel warm/hot compared to U9?

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

U8 is faulty - replace it. Grab a replacement U17 in case it's the source of the humming noise.

In chime mode you're getting the 10 point harmonic sound which is derived from output pin 7 of U17.
In computer sound mode, output pin 7 of U17 is divided through U8 twice to produce a half and quarter frequency tones and you're getting nothing from either.
This says U17 is oscillating as it should be and U8 is dead.

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:

Wow. That game sounds just like my Stern Nugent. "Outer Space" sounds I call it. I haven't fooled with it lately. Keeping an eye on this thread.

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

Since this issue seems to be caused by your Bally MPU board, let's follow up the discussion on the new thread you opened for it:

https://pinside.com/pinball/forum/topic/stern-sb100-strange-warbleerratic-sounds-lectronamo-mpu

For non functioning solenoids, check the under flayfield 1A slow blow fuse.

Try replugging the sound board ribbon cable one each side a few times in case there's a connectivity issue.
Forget about checking post #51 as previously mentioned. We've since discovered the MPU reset line is not used on the C-1 revision SB100 boards to mute sounds on powerup.