Zookeeper sound not working

nutballchamp

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I'm helping a friend fix his Zookeeper and took his boardset home to test in my machine. I got his boards running except for the sound and I'm stuck. Here's what I've done:

Reflowed solder to header pins
Replaced the 4 big caps (C22, C23, C57, and C58)
Replaced the 2 2002 sound amp chips (U29 and U30).
Swapped all socketed chips one at a time from my working sound board.
Replaced U18 LM324 Op Amp Chip (realized later this is for speech that doesn't exist)
Check Volume pot with my meter.
Checked +5v at the board and various chips. There is +12v at the sound amps (U29 and U30).
Checked one SIP resistor pack. Didn't check the others as they don't test in circuit and I only de-soldered one to test.

What's weird is that the sound is kind of intermittent. Once I got his boardset working the sound was on for about a few minutes and went dead. I powered on and off and it came up again for about a minute. After that it didn't work for a week. Last night for some reason the sound worked again. Went back to not working after I turned it off.

I've been testing the sound with my rom and video board. I also have been using my cables that work on my sound board.

Where do I start from here? I have a logic probe and scope. Should I start probing all the logic chips or check the analog amps with my scope? Wish I could understand how the circuit works more. Seems like the sound starts at the 6821 chips and is controlled by the processor? I'm kind of hell bent on figuring this out.

Thanks.
 
I'm helping a friend fix his Zookeeper and took his boardset home to test in my machine. I got his boards running except for the sound and I'm stuck. Here's what I've done:

Reflowed solder to header pins
Replaced the 4 big caps (C22, C23, C57, and C58)
Replaced the 2 2002 sound amp chips (U29 and U30).
Swapped all socketed chips one at a time from my working sound board.
Replaced U18 LM324 Op Amp Chip (realized later this is for speech that doesn't exist)
Check Volume pot with my meter.
Checked +5v at the board and various chips. There is +12v at the sound amps (U29 and U30).
Checked one SIP resistor pack. Didn't check the others as they don't test in circuit and I only de-soldered one to test.

What's weird is that the sound is kind of intermittent. Once I got his boardset working the sound was on for about a few minutes and went dead. I powered on and off and it came up again for about a minute. After that it didn't work for a week. Last night for some reason the sound worked again. Went back to not working after I turned it off.

I've been testing the sound with my rom and video board. I also have been using my cables that work on my sound board.

Where do I start from here? I have a logic probe and scope. Should I start probing all the logic chips or check the analog amps with my scope? Wish I could understand how the circuit works more. Seems like the sound starts at the 6821 chips and is controlled by the processor? I'm kind of hell bent on figuring this out.

Thanks.

OK, if you're certain that your 12V is solid (i.e. not causing the problem), and it isn't a dirty/flaky pot, and your speakers & wiring are good...

Sounds like you've replaced most of the analog portion of the circuit already. Hook up the scope, and look for a signal at the output of the amps (pin 4 of the TDA2002s). Of course, it shouldn't be there or you should be hearing it. Then look at the input to the amps (pin 1). If there's nothing there, there is no analog sound to be amplified, and the issue is with sound generation, not amplification.

Next up are the 4066s @ U24 & U28. These are bilateral switches, which are controlled by the 6821 (a PIA). They connect the +5V thru to a resistor network, essentially forming a poor-mans DAC. Use the logic probe on the 4066 outputs (pins 2, 3, 9 & 10). With the game in a mode that should be making sound, there should be activity (pulsing) on these pins. If it's lacking, verify +5 at all of the input pins (1, 4, 8 & 11) and then check for activity on the control lines (5, 6, 12 & 13). If there IS activity on the control lines, but not on the output lines, replace the 4066(s). If there's no activity on the control lines, continue moving upstream (to the 68A21).

EDIT: on second look, I think this pair of 4-bit ghetto-DACs may just be for L/R volume control. Looks like the actual sound generation is just above (on the schem) with a real 8-bit DAC (a 1408), driven by another 6821. Follow the analog audio up there with the scope, then with the logic probe on the left (input) side of the DAC.
 
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Thanks for your help Darren. Very helpful in moving forward.

I spent a lot of time on this and I think the problem is the data lines SD0 - SD7. Pins 10-17 on chip U8 is getting nothing on my probe. U8 pins 2-9 all pulse the same as my working sound board so I think that's good. U9 Pins 26-33 sometimes are always low when I turn it on and sometimes pulse but it's doesn't look the same when compared to my working board on my scope. I followed the lines all the way to U11 and the rom board and same reading. So I guess the sound board talks to the rom board? It's the same rom board and cables as when I swap in a working sound board. When my working sound board is in there I get pulses on the inputs for u11 and U25 on the rom board where the lines leave to the sound board.

The sound still works about every 20 times I power it up so it's an intermittent nightmare. Like I mentioned above the inputs on u11 are also intermittent when I power it on. Anything else I should check? Thanks.
 
I spent a lot of time on this and I think the problem is the data lines SD0 - SD7. Pins 10-17 on chip U8 is getting nothing on my probe. U8 pins 2-9 all pulse the same as my working sound board so I think that's good. U9 Pins 26-33 sometimes are always low when I turn it on and sometimes pulse but it's doesn't look the same when compared to my working board on my scope. I followed the lines all the way to U11 and the rom board and same reading. So I guess the sound board talks to the rom board? It's the same rom board and cables as when I swap in a working sound board. When my working sound board is in there I get pulses on the inputs for u11 and U25 on the rom board where the lines leave to the sound board.

The sound still works about every 20 times I power it up so it's an intermittent nightmare. Like I mentioned above the inputs on u11 are also intermittent when I power it on. Anything else I should check? Thanks.

OK, where you say "U9 pins 26-33" above, I assume you meant U8.

Sounds like found there's no activity on the sound data bus (SD0-SD7). Yes, as you discovered, the EPROMs containing the code appear to be located on another board. Just flip to the next page of the schematics and look in the upper-right corner. There you'll see the SA (sound address) and SD (sound data) lines. There are a few logic chips for address decoding, and the EPROMs (U25, 26 & 27). You might check the enable & select lines on those EPROMs (pins 20 & 18); I doubt you'll see any activity (because you said this ROM board is known-good). Also look for activity on the EPROMs' address lines (particiularly the lower ones A0-A7). If there's no activity there either, there's no reason to suspect anything on this board--go back to the sound board, 'cause I'm wondering if the 6802 (U5) is running at all.

To check the health of the 6802, first probe the reset line (pin 40). It might be low briefly at power-on, but should remain high. If it's perodically going low (or pulsing), that's a problem (CPU is being reset). Check for a clock (pulsing) on pin 39. Look for any activity on its data and address lines. Check it's power (pin 8, relative to GND @ pin 1 or 12). If it's got power, and clock, isn't being reset, but has no activity on it's address, data or R/W lines, I'd suspect it as possibly dead. Is it socketed?
 
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OK, where you say "U9 pins 26-33" above, I assume you meant U8.

Sounds like found there's no activity on the sound data bus (SD0-SD7). Yes, as you discovered, the EPROMs containing the code appear to be located on another board. Just flip to the next page of the schematics and look in the upper-right corner. There you'll see the SA (sound address) and SD (sound data) lines. There are a few logic chips for address decoding, and the EPROMs (U25, 26 & 27). You might check the enable & select lines on those EPROMs (pins 20 & 18); I doubt you'll see any activity (because you said this ROM board is known-good). Also look for activity on the EPROMs' address lines (particiularly the lower ones A0-A7). If there's no activity there either, there's no reason to suspect anything on this board--go back to the sound board, 'cause I'm wondering if the 6802 (U5) is running at all.

To check the health of the 6802, first probe the reset line (pin 40). It might be low briefly at power-on, but should remain high. If it's perodically going low (or pulsing), that's a problem (CPU is being reset). Check for a clock (pulsing) on pin 39. Look for any activity on its data and address lines. Check it's power (pin 8, relative to GND @ pin 1 or 12). If it's got power, and clock, isn't being reset, but has no activity on it's address, data or R/W lines, I'd suspect it as possibly dead. Is it socketed?

Sorry, yea meant U8 pins 26-33.

I did swap 6802 with my working board at one time but didn't check anything except for the reset line which was good. I'll check again and everything you mentioned now that I understand a bit more. Thanks!
 
Sorry, yea meant U8 pins 26-33.

I did swap 6802 with my working board at one time but didn't check anything except for the reset line which was good. I'll check again and everything you mentioned now that I understand a bit more. Thanks!

IF the 6802 @ U5 is a good one (determined so by swapping), then possible issues include:

-clock issue (3.68MHz generation circuit is in the bottom-center of the schem, output should be on TP9 test point)

-bad buffer(s) (U11, U4, U6 or U12)

-bad code on EPROMs? (but I'd still expect to see some activity as it reads and executes the bad code...)

Looking at it... I can't figure out how the main CPU talks to the sound CPU...
 
I'm throwing in the towel on this one. Clock, reset, and voltage at chips are all good on the sound board. The SD0-SD7 lines are intermittent and will sometimes be stuck low, pulse or a different pulse when board works. The SD0-SD7 data lines are also intermittent at the output of the Rom board at J5. This is the same rom board and cables that always work with my working sound board. I swapped out Pia chips and cpu with known working ones. Sound worked second to last time I fired it up. Went back to issues above once I powered it off and on.

Does anyone work on these boards? Would love to find out what the issue was.

Thanks for the help Darren.
 
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