Is it possible to bench test a stern sb100? I can test the different voltages at the test points by hooking it to a bench power supply. I can hook it to a speaker and jump the volume pot pins but how can I trigger a sound?

Has anyone been able to do this?

Thanks @barankdl that makes sense. I'll Yank the mpu too. This is my first sb100 I've worked on so I'd like to have it on the bench.

Now I just have to find my notes on how to cheat the 7th flash.

I don't have the experience yet to know if this would work but I wonder if it wouldn't be easier to use an old SDB to drive a chime box instead of fixing this sound board

I've actually got 2 of them

Board #1 has no tone on multivibrator #2. The voltage on TP3 is 0

Board #2 (that I got on ebay for $10!) has good voltages on all test points but no audio output

Trying to decide which is the easier repair.

Great advice. Thanks

Can I jump the volume pot with a lead like a williams game?

U8 was the culprit on board 1. Pin 3 had 1.5V. Compared against U9 pin 3 and 11 and did not match. Chip tester reported Err but I was not sure it supported this chip anyway. Pulled U8 from board 2 and chip tester reported ok. Swapped into board 1 and I have all sounds.

I'd like to do the Sound Quality update on it http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Adjusting_the_Sound_Quality_on_a_Stern_SB-100_board and then I need to figure out the right pot settings to put the tones in the correct place.

Haven't looked at board 2 yet. I'll inspect the board and pull and test those chips to see if something stands out

@quench, @barakandl, and acebathound thanks for the help

found it here: https://pinside.com/pinball/forum/topic/tech-hot-hand-sb-100-no-sound/page/2#post-3930780

Thanks!

Much better! Thanks for the tuning tip Quench

Interesting development. #1 SB-100 locks up the mpu on boot. Previously I had been using an altek while I fixed the mpu-100 and it appears to have diodes on the 32 pin connector and avoided locking up.

I traced all of the lines on the 32 pin header on both boards and verified they had connectivity back to the source. I also tested the 32 pin cable to eliminate that. I then started pulling the wires 1 by 1 on the cable to see if I could identify which was causing the lockup. Pin 25 is the culprit. Strangely enough the board works fine with it disconnected but that is not the solution.

This is a Rev B board and it has a weird config near U6 with a resistor in place of a jumper (near R93 on a rev c board) and a cap that jumps from a resistor leg to C52. The resistor tests fine. I'll pull and test U6 (74107) and replace the cap 4.7uf tantalum and see if this fixes the problem.
IMG_20180214_175337209 (resized).jpg

I do occasionally get a squelch on power up. That tells me maybe the cap is shorted. I'll check it out

On the Rev b I have a resistor where R93 goes on a Rev c. The cap is attached to the leg. Both of my Rev bs have it

Still no luck. The 74107 (U6) tests bad but I don't think my tester is correct unless both of them are bad. The sound card still works if I can get the mpu to boot.

Swapped the capacitor on the reset line and it did not fix it. I need to understand what this line is trying to do i.e. start high and go low or vice versa so I can test it in the game.

I ordered more 74107 so I can try that as well.

Results:

With Sound card disconnected U9 - 40 starts low and goes high as expected
Connected stays low. Shorting 39-40 starts MPU

Interesting Find: I pulled U6 from the board and the reset stays low. According to the schematic it is a straight connection from Pin 25 to U6-10. None of those are tied to ground. Investigating deeper

Ok this is fixed. Turns out the CD4013 at U9 on the SB-100 at was bad. U8 was bad and replaced earlier. I should have suspected this but the schematic doesn't show a relationship to U6. Now I know better.

Thanks to Quench for helping me find the solution. As much as a pain that this was I think I learned some valuable diagnostic skills here.

Here's some detail for the next guys:
Pin 25 of the interconnect comes to R93 (on Rev C, unlabeled on Rev B). This is a 47K resistor. The other leg of the resistor has a 3.3uF tantalum cap soldered to it that is also connected to the top hole of C52 (ground). C52 is otherwise unused on a Rev B board.
U6 Detail (resized).jpg

Looking at the back of the board it is easy to miss that there is a jumper from the left leg of the resistor to the top of C50. C50 was not shorted so this would appear to be a dead end except that the trace from C50 continues on to a leg on U22 which is a 78L05 in a TO-220 package. This also test fine...
U6 Detail Back (resized).jpg

Goin up the trace comes to U8-14 and U9-14. Replaced U9 and back in business.
U9 Back Detail (resized).jpg

NOTE: this pics are from my parts board. I will clean and repair now that I have an idea what to do. Please don't mind the flux!

Started working on Board #2. 7V on U20 and U21 and 10V on TP9. U18 tested bad and I had a replacement. U14 works in my other board but in this board I'm still not getting audio.

I'll take a look at the signal path. I should be able to.pick up some of the audio on my USB oscilloscope. I've been looking for a good use. If U14 is good.i should be able to see some audio at U20 and U21 and that should demonstrate that those don't work.

I used a 4.7 as I had it on hand. The board originally had a 3.3.

I'll have to trace it out but I'm guessing TP6. It takes a long path past Q18. I've got a tournament today and I'll trace it out tomorrow.

Looking at my board it exactly matches the schematic on techdose for a Rev C in regards to Q1. The emitter is connected to the + side of C18 and R24 which connects to the - side of C10. The positive side of C10 is connected to U4-10. The Collector of Q1 connects to the - side of C18 and then R85 and R86. I don't see any additional jumpers associated here.

My guess would be TP1