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Centris 660av No Sound Output in MacOS

commodorebob

commodorebob

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Joined
Jun 30, 2015
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33
Hi Everyone, I recently acquired a Centris 660av that had a bad case of cap leakage. Luckily, I was able to clean the board and replace all of the capacitors.
The machine finally worked, except for it had no sound at all, after doing a bit of looking, I noticed that the DA7052A amplifier chip was really hot, to the point of burning my finger.
I replaced the chip and finally got I chime! However now after installing MacOS 7.6 on a BlueSCSI, I realized that there was no sound coming from the OS, and when I try to go to the audio output settings, I get a hard crash.

Does anyone know what would be going wrong? Is there another chip that could have been taken out related audio output sensing in the OS? Maybe it's something software related that I am not aware of?
 
Just looking at the chips around the area, there is a 2082C OP-AMP that looks green and crusty looking legs, but I'm not sure what that would go to.
 
Oh wow, sure enough, I removed that chip with my hot air station and two of the legs stayed on the board without any force applied to the chip, and the other two broke off with the slightest touch.

I'll report back after the new 2082CD comes in, but I'm fairly confident it that will be the fix.
 
Glad you were able to track it down. I have a Centris 610, and I've given it the "Dirtiest Mac" award, previously held by the IIci. Somehow the capacitors leak even more than the IIci, which is an impressive feat.
 
Well unfortunately that opamp was not the problem. After replacing it I was stuck with the same symptoms. However the chime does come through a bit more clearly (though that may be a placebo).
I wonder of it could possibly a software issue since It does at least chime. What is strange is that the volumes area in the sound settings is corrupted and of course when I go into sound out it crashes completely.
I'm mainly just not too familiar with the audio circuitry on this era of macs.
 
The 660av used the AT&T DSP for sound. The OS version you are using might not support it.
 
If the amp was that corroded, you most likely have more cleanup to do. I would wash the logic board thoroughly and scrub the surface of the board with a soft bristled brush, and between the legs of the ICs (GENTLY). You probably have more electrolyte shorts, and probably some broken traces and lifted pins.

You'll have to check the connections between ICs one by one as well using resistance mode. Continuity won't help you here because if the traces have been damaged, they can get unusual resistance readings higher than a short, but lower than 50 ohms, which a multimeter may say has continuity, but really doesn't.
 
czunit said:
The 660av used the AT&T DSP for sound. The OS version you are using might not support it.
Click to expand...
This could be it. I'm using Mac OS 7.6. I will try installing 7.5 tomorrow to see if that will work since that is something I can easily try out.
 
GiGaBiTe said:
If the amp was that corroded, you most likely have more cleanup to do. I would wash the logic board thoroughly and scrub the surface of the board with a soft bristled brush, and between the legs of the ICs (GENTLY). You probably have more electrolyte shorts, and probably some broken traces and lifted pins.

You'll have to check the connections between ICs one by one as well using resistance mode. Continuity won't help you here because if the traces have been damaged, they can get unusual resistance readings higher than a short, but lower than 50 ohms, which a multimeter may say has continuity, but really doesn't.
Click to expand...
I think that I have gotten all of the old cap juice off the board. After I removed the old caps I brought it down to the sink and gave it a good (and careful) scrub with soap and warm water and let it sit for a week to try (from Monday to Saturday). Then I replaced the caps. I am thinking it could be a trace. I'll use the schematic to pinpoint trace down if there is any broken connection.
 
commodorebob said:
This could be it. I'm using Mac OS 7.6. I will try installing 7.5 tomorrow to see if that will work since that is something I can easily try out.
Click to expand...
Try installing os 8.1, although it look like 7.1 and later were supported I think there was a specific assist for the dsp.
 
czunit said:
The 660av used the AT&T DSP for sound. The OS version you are using might not support it.
Click to expand...
i don't think that's true.

commodorebob said:
This could be it. I'm using Mac OS 7.6. I will try installing 7.5 tomorrow to see if that will work since that is something I can easily try out.
Click to expand...
7.6 should be fine. these machines came with 7.1. anything 7.5+ will install the necessary drivers and enablers for a 660av.

8.1 should not be necessary... and will be dog slow on that 25mhz 040 anyways.
 
7.6 absolutely supports the 660av, as should 7.5.

What's throwing me for a loop is you hear it chime at all, so it's taking the sample from ROM, decoding it, converting it and sending it to the speaker amplifier. Apple's hardware support outside of enablers is more or less idiot-proof and I don't think I've ever seen a mac that needed an INIT just for basic sound.
 
NeXT said:
7.6 absolutely supports the 660av, as should 7.5.

What's throwing me for a loop is you hear it chime at all, so it's taking the sample from ROM, decoding it, converting it and sending it to the speaker amplifier. Apple's hardware support outside of enablers is more or less idiot-proof and I don't think I've ever seen a mac that needed an INIT just for basic sound.
Click to expand...
That is the strange thing for me too. Just to me sure list night I installed the original System 7.1 that was specifically meant for the 660av and I get similar results. Only a chime, no input devices listed, and when I go to the audio output list the finder crashes, but unlike Mac OS 7.5 or 7.6 it is a able to restart the finder and recover.

To me it seems like the most vital bits of the system are working, it just seems to me that the OS is not able to enumerate the audio output device properly. It could me that I am focusing too much on the upstream of the audio amp chip and need to look elsewhere?
 
Thanks to the schematic that finkmac provided, I think know where to check next. Since I have audio output and have replaced the audio amps I'm going to assume that U12 and U25 are good, as well as the output from the Singer chip (U29). So this evening I will check some of the lines coming from that, specifically. Since it's having issues with detecting anything in the OS, the sense pins seem logical to check. I'm hoping it's a bad passive or a bad trace because while it looks possible to get a replacement ASCO 3200 chip, I really don't want to try it with my small hot air station.
 
Well after taking a very close look at the schematic and the board, I realized that RP89, a 4.7K resistor array is straight up GONE. I thought they were just unused pads since it fell off so cleanly. C49, while I'm pretty sure still works, looks terrible. I ordered both parts so they should be in next week.
Two of the resistors look to be a pull up resistors for BIO Line 5 and 6 on the DSP, and they also pull down BIO7 and several other pins on the DSP. If the DSP is directly tied to the sound system and other posts on this thread suggest, this may be the cause of the strange behavior.

RP89.jpegbad_cap.jpg

schematic.png
 
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You have some pretty nasty corrosion on the legs of the DSP3210 in a rather troubling spot, the parting line on the encapsulation where the legs come out, all along the side with the capacitors.

Very possible that capacitor electrolyte has wicked inside the body of the chip and caused damage to it.
 
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