Sorry, can you explain exactly what you've just tested? Depending what you've done this result is either good or maybe bad.

I got them reversed in my previous post. I think I've confused myself with what I asked you to do

Ok, contrary to what I said in post #49 I'd expect pin 4 on U20 to be louder than pin 6 on U22 when you're injecting the signal generator tone, because when you're injecting it into pin 4 on U20 it should then get amplified by U22. When you inject the tone signal on the output pin 6 of U22, you're not getting that stage of amplification so pin 6 of U22 should have been quieter.

I think it's time to order two 741 op-amps and first replace U22. If it revives the sound effect volumes, then replace U21 for the speech side.
LM741 / UA741 op-amps are common and very cheap.

If you're in a position where it's going to take a week to get the op-amps, then just unsolder and remove U22. Turn all the volume controls up and start a game. If the sounds during game are the same quiet level as before, I think it would give more evidence to U22 being faulty (dead).

I'd say that's a good sign U22 was faulty.

U22 doesn't have anything to do with speech. It's the other op-amp at U21 that's in the speech path.
The manual explains when speech (and what phrases) occurs. See below.
When the ball enters the lower playfield the speech should make an "ouuuw" sound. When the ball gets kicked back up to the main playfield it will speak one of the "Re-Entry..." phrases.
Spell the drop targets in order to get the "G-Force accelerated" speech. All other speech happens at random times.

BlackHole_Speech.jpg

There's actually a couple of sound effects that are just a scratchy type noise which is normal, for example when you hit the drop targets in order (strange choice of sound effect for a good achievement).

If you want, you could get some (two) replacement DACs just incase. The originals were "1408-6" which are obsolete, but "DAC0808" should be a suitable replacement. If you get them make sure they're not surface mount versions, you want DIP version.

Got to my Black Hole in storage today. Took some crappy photos with my oscilloscope.
The U22 op-amp appears to simply be acting as a buffer - it's not really performing much amplification.
The test button on the sound board causes it to play a tone for about a second. Press it again and it plays tone again plus maybe something else? Press it a third time and it produces some speech, can't exactly remember what it said but something about "completed". Press it a 4th time and it starts from the tone again. I couldn't take a photo of the tone wave as I ran out of hands - at pin 6 of U22 it was a sawtooth waveform between 0 volts and 6 volts.

The middle leg of pot R16 produced a signal of about 1 volt peak to peak when speech was playing. Sorry, not enough hands to take a snapshot

The output of my amplifier is clearly distorting (my R15 pot needs to be adjusted to reduce the music volume going into the amp).

The last waveform was very high frequency noise - it's a positive reference voltage used by the U20 DAC. The negative reference voltage on the DAC at pin 16 measured -7 volts.

Check the DC power voltages on the U20 DAC, they're listed on the schematics.
Pin 3 should be -12 volts
Pin 2 should be ground (zero volts)
Pin 13 should be 5 volts

Then try to measure the pins as per below on your oscilloscope to see what amplitude you're getting in relation to my waveforms.

Pin 2 of U22 with background game music

Pin 6 of U22 with background game music

Amplifier output at pin 7 of connector P1 with background game music

Pin 14 of U20

The line is probably going off the scale on this measurement. Can you change the oscilloscope from 2 to 5 volts per division and retest?

BTW when you short the probe input connectors together, where does the blue oscilloscope line go on the display? is it along the vertical centre of the grid?

Grab the latest version of the manual - it explains calibrating the unit.

https://github.com/SeeedDocument/DSO_Nano_v3/raw/master/res/DS201V_4.22%20User%20Manual%EF%BC%88Increase%20the%20alignment%20and%20hidden%20reference%20line%EF%BC%89.pdf

Preferably it's better to connect the oscilloscope ground to a ground point on the sound board. Probably the most convenient spots are either the lower leg of resistor R9 (between the R6 and R13 pots bottom right of the board), or the leg coming out of the top of capacitor C27 lower left corner of the board.

Since we're measuring voltages that are going negative, it's best to set the oscilloscope so the reference for zero volts is along the center in the grid. Go to the "Yn" function and adjust the "Y Offset" so when the probes are shorted to each other, the blue signal flat lines in the middle of the grid. This is generally the way you look at analog signals such as audio. With experience you'll get the hang of where to reference zero volts on the grid depending on the voltages you're measuring.

If you're ever analysing digital logic signals, then you can move the blue line near the bottom of the grid since digital signals are positive. I usually put it on the first step so I can see any minor negative swings.

BTW, go to "Tr" on the menu and select "Hide-Tri" to remove the dotted green line. We're not using the Trigger feature.

Yes, this unit can only output a square wave and looks like it is logic level range (between 0V and 5V).

Once you've got the blue oscilloscope line centered, redo this measurement still at 5V per division.

I’d like to take this opportunity to thank both of you guys for such great posts in this thread... it is very educational.

The output is almost distorted at full negative voltage. With the oscilloscope hooked up to pin 6 of U22 in game background music mode, adjust the amplitude at pot R13 until the blue line rises and it hopefully produces some sort of waveform.

Then set the oscilloscope to 2 volts per division. In game mode, confirm that you get activity on pins 5 through to 12 on the U20 DAC. You should see activity between zero and 5 volts.

We haven't even looked at the speech side of things yet. In Game Over (attract) mode do you see any activity on the oscilloscope at pin 15 of the U14 speech chip when you press the test button on the sound board? Speech is produced every 3rd press of the button (wait a second between presses). If you're looking at the schematics, that pin should show activity between zero and say 11 volts because it's driven by transistor Q2 so set the oscilloscope to 5 volts per division.
How about the output of the speech chip (pin 20 of U14), any activity there?
What about output pin 4 of the U19 DAC used for speech?
And the output pin 6 of the U21 op-amp?

In the mean time have a quick look on ebay for sources of the DAC chips. Look for MC1408 and DAC0808. We might get to the point that they're next in line for replacement so find out what options you have.

When adjusting pot R13 did the blue line at least move upwards while probing pin 6 of U22 ? I guess you're not seeing a wave because it's too small in amplitude to see when we've got the oscilloscope at 5 volts per division. I think you were getting waves on this pin when your oscilloscope was set low at 10 millivolts per division on the previous page.

Well on the surface it indicates that DAC is not losing amplitude resolution due to a lack of digital info. The digital info is all active.

You mentioned this in your post directly after I posted my graphs. On my graph, pin 14 of U20 is around zero volts, yet your wave has it sitting at 12 volts.
I'm looking at the DAC datasheet and it talks about pin 14 having 2ma of current. The schematics show pin 14 connected to +12volts via resistor R11 which is 5.6k ohms in value.
Using Ohms law, (voltage = current * resistance) 2ma times 5.6k ohms (0.002 * 5600) = 12 volts. With one side of the resistor being connected to 12 volts, the ohms law calculation says the other side of the resistor which is connected to pin 14 of U20 should be zero volts (which is what I got). Yet you are getting 12 volts there indicating there is no current flowing through R11 from U20. Hmm... is this evidence U20 is faulty? I wish I had access to my game for further checks.

With your oscilloscope on 5 volts per division, can you redo a waveform of pin 14 of U20 plus also pin 15 of U20. Also waveforms of the same pins (14 and 15) of the DAC used in the speech path at U19. These two pins are positive and negative voltage references for the DAC.

Are they cheap?

How are you going here, are you getting frustrated this isn't resolved yet?

Is anyone here watching that has a Black Hole who can take some DC voltage measurements with their multi-meter of these ^^^ four pins on their sound board?

Both your pin 14 DAC measurements are at 12 volts DC which disagrees with my U20 pin 14 DAC measurement and what's stated in the DAC datasheet. Is it possible there's been some high voltage spike (possibly the 30 volt rail??) on the 12 volt rail to the sound board that's killed the DACs?
The speech chip at U14 also has the 12 volt rail connected to it though it's dropped to 9 volts via a 3 volt zener diode marked as CR2 on the schematics. Datasheet for the speech chip says maximum supply voltage is 20 volts. These speech chips are virtually unobtainable so the worry is if there was a 12 volt power surge, is it also damaged.

The LM741 op-amps at U21 and U22 are also connected to the +/- 12 volt rails. Your original UA741C op-amps were rated to +/- 18 volts DC max. Since you've changed the op-amps and it's made no difference, it's possible the originals were ok.
Having said that on my first two waveforms, the difference in voltage peak to peak between the input and output of U22 shows a very modest gain of about 1.2
You posted a picture above of U22 input pin 2 having about 1 volt DC, meanwhile your pin 6 output was off the scale at negative 12 volts. That is substantial gain and with the R13 pot turned all the way in one direction, the gain should have dropped to about 1.

I wonder if your R13 pot is bad. With the machine off, set your multi-meter to resistance mode. What resistance do you measure across pins 2 and 6 of U22? This is where the R13 pot is connected across. The schematic says it's 10k ohms so you should read this or less depending where the pot swipe is adjusted to. Do the same across pins 2 and 6 of the op-amp at U21. Again it should be 10k ohms or less because of pot R6.

The DAC0808 version is still available at Mouser, Digikey and Jameco. Is shipping any cheaper from these suppliers for you? There's always getting them through China via Ebay/AliExpress for peanuts so long as you're prepared to wait a month or so for delivery.

Nice work. My guess is that the section where the spring sits would have had a bend going up at the inner side to prevent the spring from sliding down into the centre of the wireform (if that makes sense).

Nah, leave the original U21 in for now.

If there was a voltage surge on the +12V rail and damaged the DACs, it doesn't necessarily mean that U14 died too. The max rated supply voltage of U14 is over double what it's powered at in the game. I was just mentioning that it was a possibility and if so you could have a hard time finding a replacement. U14 is a speech chip, it doesn't affect other sounds.

Not sure what all the mods are on the back of the sound board but they kind of look like they were done at the factory.

Finally some progress!

The background sound changes when you go to the lower playfield; from memory it makes a changing wind type noise (kinda like you're floating in space effect?). The background music returns when the ball re-enters the upper playfield.

Have you first tried re-adjusting the R6 and also the R16 pots for the speech?

If you keep pressing the test button on the sound board does it ever produce speech?

If I remember right, when you tilt the ball in play the game repeats saying the word "Tilt" about 5 times and lowers the pitch each time.

I'm attaching the sound/speech board schematic below for reference.

Before presuming the speech chip is suspect, we need to see if it's getting activity on all the input pins (pins 14, 13, 12, 11, 10, 9, 3, 2, 7, 8, 15, 16) when it should be talking. Set the blue line offset to the first grid line above the bottom of the screen and the voltage to 2 volts/division.
Probe all these input pins with the oscilloscope when repeatedly pressing the test button on the sound board.

Sound.png

Hope you're feeling better..

Try this. Press and *hold* the test button on the sound board. This should repeatedly cycle through the sound tests which will beep, beep then speak and repeat every 2 seconds. I can't work out what it's saying from the emulator I'm running but after the two beeps you should get some activity at the voice chip. Redo the checks in my previous post.
A couple more pins of interest to check are:
pin 22 of the U14 speech chip which is the audio output pin
pin 14 of the U19 DAC
pin 6 of the U21 op-amp - what you see here should be similar in frequency to pin 15,16 of the voice chip.

When holding the sound test button pressed, did you notice the two beeps then silence (when it should have been speaking), then two beeps then silence and repeat?

So you're only getting a DC voltage? I expect this should be pulsing when the speech chip is told to talk.

Probe pins 5 through to 12 at U19 to see what activity the DAC is getting from the CPU.

Sorry I meant pin 4, not 14.

Interesting, well you're only getting the two beeps and there's no time break when it should be playing speech. From experience that tells me the board might think there's no speech chip or thinks it's disabled so doesn't perform any test for it.

BTW, the manual says the sound test button should only be used in game over (attract) mode.

I just noticed the manual has more details about the sound/speech board test procedure - see the flowchart diagram below.
Actually near the end of the flow chart it has the tone repeating when dip switch 1 is ON. Can you do me a favor and flick all those 8 dip switches on the sound board to the opposite position and re-power the game to see what happens? Your 8-way dip switch block doesn't clearly indicate what's on and off. I'm almost wondering if all those dip switches are set opposite to what's wanted..

I was at my Black Hole very briefly today. Holding the sound test button plays two beeps then the speech chip says "complete" and repeats the beeps/speech.
I had a logic probe with me and probed the inputs to the U19 DAC and got the following during speech.
Pin 5 stays low
Pin 6 is high with a brief pulse during speech
Pin 7 stays high
Pin 8 stays high
Pin 9 is high with a brief pulse during speech
Pin 10 is high with a brief pulse during speech
Pin 11 is high with a brief pulse during speech
Pin 12 is high but goes low during speech

What happens at pin 8 of the U14 speech chip? It's the only pin that provides feedback to the CPU. According to the speech chip datasheet, when the speech chip receives a command from the CPU, pin 8 should go low telling the CPU it's received it. When the speech chip is finished with the command pin 8 should go high telling the CPU it's ready to receive the next command.

Probe pin 8 during the speech test. I suspect it won't be doing anything.
Next, probe pin 8 as you power on the machine and take special notice of what it does. You'll probably have to do it a few times to get an idea of what it's doing. The problem here is that the CPU might try to test the speech chip very soon after the game is powered and so it will be difficult to get an accurate idea. You might have to get the oscilloscope to record the pin 8 waveform at power on so you can go back and look at it.

For reference, this is the only online source I've found for the speech chip - not cheap...
ebay.com link: SC01A SemiConductor CASE DIP22 MAKE Generic

BlackHole_SoundTest.png

Can you do a continuity test across dip switch 1? Does the meter show it changing when you flick that switch? Make sure to leave it off.

Ok, follow the test procedure in the flow chart from start to end. What happens?

Please probe pin 7 of the U14 speech chip when it should be speaking. You should see it pulsing telling the speech chip there's data for it to receive.

Hold off. For one thing you might be able to find a cheaper source locally/in the US with guys who can repair these boards. You might even be able to buy a working board for that price??

The behavior I mentioned is what I expect based on the datasheet. I won't be near my game for some weeks so can't confirm if what you're seeing is right.

Sorry for the delay, my turn to be under the weather..

That's what it should be doing.

Question is why is the board playing a tone instead of speech (silence if the speech chip is faulty) during the sound test.
Presuming you socketed the new DACs and Op-Amps, I would swap them around and see what happens just incase one on the speech side is suspect.

Might be time to check the pinball/arcade board repair guys in the US to see if any have that speech chip. It's a Votrax "SC-01-A" speech phenome chip.
Maybe even Pinball Resource have them being the Gottlieb guys.
This speech chip was also used on some old arcade video games such as Q*Bert.

Great find!
Lets hope the Black Hole finds its voice again!