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Performa 630 DOS - No Audio

Phipli

Well-known member
Hello folks!

I've been tidying up a Performa 630 DOS Compatible that was found at a dump a good few years ago, it has some corrosion damage due to being left outside (rust on ports, couple of corroded pins on the processor, some relatively minor blemishes here and there, plus it looks like the battery leaked a little. The most notable issues were that the internal CD didn't work and that there is no audio. It also sporadically crashes - it either freezes, or progressively gets slower until it basically stops... as if something was triggering millions of interrupts. The computer functions perfectly if I swap in another P630 logic board (don't ask, my dad likes them, so we have spares), but the troublesome board is the only DOS board. The DOS logic boards are different - they have two RAM slots populated is the obvious difference, but they also have additional holes for the DOS board's standoffs, and an additional connector, I believe for the pass-through video (the footprint doesn't even exist on the regular P630). @Bolle mentioned that the DOS 630s have more in common with the P580 boards.

So far I have replaced the CPU with one that doesn't have a broken pin (see "Sad CPU.jpg"), done a bodge wire repair of the SCSI termination for the internal CD ("Bodge 1 (SCSI).jpg"), done a bodge repair on a broken / lifted trace near the serial ports ("Bodge 2 (Serial).jpg"), renewed the solder on some pins for U24 because it looked crusty ("U24 Resoldered.jpg")... and recapped it ("LB Top Recap.jpg"). Not because it looked like it needed it, but because I thought that there was a chance that dodgy audio might be due to caps that forgot what capacity they should be.

I continuity tested the battery damage, and had continuity on all vias other than one of the two (related) vias highlighted in "Battery Damage 2.jpg". I realise that there is a chance that the probes might have helped with this, but I suspect the pins all relate to internal SCSI termination... which works now :)

Given the audio works with another logic board in the computer, the fault is almost certainly on the logic board. Given the CD audio pass-through doesn't work, it is likely in the mixing / amplification stage or later of the audio system. I think this means U1 (DFAC II?) is a possible suspect, but it is a custom chip unfortunately. See "Arch Audio.png" (Thanks George).

I've attached a number of photos that might be helpful. Are there any known causes of audio issues on 630s or similar machines? Does anyone have any suggestions?

Thoughts welcome, solutions extremely welcome :)
 

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Phipli

Well-known member
I also tested sound in with a PlainTalk mic. It didn't work either, so it really feels like the DFAC II isn't running at all.
 

max1zzz

Well-known member
DFAC II's are known to go bad so it is entirely possible that that is your problem but given you have battery damage and the machine has possibly been left outside I would try and verify all it's traces are undamaged

It may be worth having a look at the colour classic schematics (which can be found here: https://archive.org/details/Macintosh68kSchematics) as although it is a completely different machine it also uses the DFAC II so it will give you a good idea of how the DFAC's circuits should be wired and how it connects to the system
 

Phipli

Well-known member
Thanks @max1zzz, much appreciated.

Downloading it now. It will give me clues to the pinout and more, extremely useful.

I'll need to take care because they wired the DFAC slightly differently between different macs. The... 520? and others have it controlled from the cuda chip, while it is hung off the "PrimeTime II" in the 630. This is handy if anyone else is interested :


I've found some DFACs on utsource but haven't requested a quote yet. I could borrow one from another machine, but don't want to end up with two mute machines when it turns out they're extremely heat sensitive, or something.

Regarding the damage, it is less bad than it sounds. All things considered it got off lightly. I've spent a good few hours searching the board and haven't seen visible trace damage near the audio circuit, although there might be something under a chip. I might test the SOIC chip on the reverse of the PCB to the DFAC as that was the only local staining. Also give me a chance to look under it.
 

Phipli

Well-known member
Handy, found these with my TL866. I'll need to take the back cover off for clearance (the other way it clashes with the audio jack) but I'll be able to check pins more easily with it running. Not sure what I'll test yet. Took it easy today, last day of holidays.

SOIC adapter will do for the 74HC02 I want to test.
 

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Phipli

Well-known member
Pulled U24, the OR logic chip on the reverse of the audio chip where there was a small amount of crustyness on the pins. Other than the adhesive it looks clean underneath and the chip passed a logic test in my TL866. DFAC II is looking more and more guilty.
 

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360alaska

Well-known member
You best bet is probably to find a LC 580 logic board. It is the same as a 630/640 dos logic board.
 

Phipli

Well-known member
You best bet is probably to find a LC 580 logic board. It is the same as a 630/640 dos logic board.
I had a look previously, but there are none at reasonable prices on eBay at the moment. Regardless, this board almost works so I would still try to fix it. Troubleshooting is a nice bit of mental exercise and working on a faulty board is excellent practice for when it really matters.

I've spent exactly nothing so far, and might get a working DOS 630 and a load of entertainment out of it. Until it gets frustrating it sounds like a good deal to me :)

Next step (DFAC II) will possibly need a bit of expenditure, either a cheap trashed donar board (anyone got a battery damaged 040 logic board?) or a chip pull, plus I've ordered a nozzle for my hot air gun that is better suited to removing the existing chip.

I'm in no hurry, I have a vanilla 630 board in the chassis at the moment, and installed the TV/FM card and AV card from my dead 6500 for fun. Spent some of today listening to the radio on it :)
 

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max1zzz

Well-known member
I can proably spare a DFAC II, Let me have a look through my pile of scrap boards and see what I have
 

Phipli

Well-known member
Woooooo!
View attachment VID_20220921_234533.mp4
After dropping in and out of working on this board for months I've finally got sound working.

For reference, I worked out that the 7905 was burnt out, so I checked and found a near short on the negative 5v. I assumed it was in the sound circuit but hadn't found it after removing most of the sound chips, caps and diodes.
This evening I fed -5v straight into the output pads for the 7905 and watched the board with a thermal camera - one of the serial 26LS30 chips started getting toasty! Looking closer the serial port looked bad - I could see PCB delamination, crazing and dodgy looking vias. After removing the port I found soot marks, possibly spattered metal. I think this machine was hit by lightning through the serial port!

The short cleared after I removed the 26LS30, so I fitted the DFAC II, new 79M05 and various other bits of the sound circuit back onto the board and tried it. At last! Sound!

I wanted to get this board working because it is a DOS Compatible 630. The DOS card doesn't fit my other 630.

I know I'm missing a serial port and the board isn't in great shape, but I'm over the moon to hear it chime.
 

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joshc

Well-known member
Nice one, that was quite the project! Seems like a lot of Macs around this time (1992-1994?) have audio circuit issues. I've had audio problems on the 475 and 650 as well and I know the 840AV can have issues too.
 

Phipli

Well-known member
Nice one, that was quite the project! Seems like a lot of Macs around this time (1992-1994?) have audio circuit issues. I've had audio problems on the 475 and 650 as well and I know the 840AV can have issues too.
Thank you :) Perhaps it is often from lightning struck modems? I remember there were loads of "doorstop" modems about from lightning back in the day.

Or just a not very resilient audio circuit. Or the change from mic level to line level sound input?

Weirdly everything with sound is fine now, except the DOS card MIDI. The normal sound on the SB16 works ok, but the MIDI is distorted and hangs. Progress though. Sadly I don't have another DOS card to switch the sound card and see if it is the sound card, DOS card or logic board.

I've still got that second 475 to finish fixing. Its 90% there. Had to hide it away when family visited and haven't fetched it back out yet.
 

Phipli

Well-known member
IMG_20220922_103818.jpg

For now I also removed the 26C32 just in case as it likely too a pummeling. And yes, that is a 25MHz LC processor. I wasn't going to put anything good in the board to test ;)
 

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cheesestraws

Well-known member
Seems like a lot of Macs around this time (1992-1994?) have audio circuit issues. I've had audio problems on the 475 and 650 as well and I know the 840AV can have issues too.

Thank you :) Perhaps it is often from lightning struck modems?

It's usually the sound circuit itself that kind of disintegrates. In this case, the sound circuit was more or less colateral damage, it just lost a power rail :)
 
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