Performa 630 DOS - No Audio

[Daniël]

Perhaps it is often from lightning struck modems?

The DFAC chips in Macintoshes tend to be closely surrounded by the electrolytic caps of the sound circuit. They tend to just roll over and die once they eat enough cap goop. It's pretty similar to the UE8 and surrounding logic chips in the SE/30, being positioned right next to the sound circuitry and its corresponding caps.

 

[treellama]

I have an LC 630 Dos Compatible that makes constant staticy sounds out of the speaker when turned on. It seems to work otherwise just fine. I tried plugging in external speakers too and those also made the noise. I know it is a different sort of issue, but seems somewhat similar to what you went through. Any tips on things I could test out to figure out the source of the problem? The board itself seems functional and looks pretty clean.

My Performa 640 DOS Compatible makes this sound very infrequently, even after being recapped. I’d love to understand why. I like the suggestion of removing the sound card on the DOS card. I could do if for mine, but it would be difficult to tell if it made a difference.

 

[superseth]

Thank you so much for the reply.

1) No I haven't recapped it yet, outside of the sound things seem ok and nothing leaking so I was hoping to isolate the problem before starting any board surgery.
2) After reading this list I tried removing the daughter card and that got rid of the constant static! The daughtercard looks ok? But yeah that seems to be part of the problem. I still don't get the clearest sound out of the machine, looking to find some kind of music to play on there to test further.

 

[Phipli]

Thank you so much for the reply.

1) No I haven't recapped it yet, outside of the sound things seem ok and nothing leaking so I was hoping to isolate the problem before starting any board surgery.
2) After reading this list I tried removing the daughter card and that got rid of the constant static! The daughtercard looks ok? But yeah that seems to be part of the problem. I still don't get the clearest sound out of the machine, looking to find some kind of music to play on there to test further.

I suspect one of your opamps on the PC sound card (that you removed) is failing, although it might be something else in the sound circuit - I can't really tell without being hands on. There are two of them on the board.

5pcs TLC2274C TLC2274CDR SOP-14 Integrated Circuit IC | eBay

◆ Qty:5pcs.

www.ebay.com

I got those.

 

[superseth]

I ordered some up - I haven't remounted a chip before but I have a IIci that I think needs a similar removal and cleaning so I'll perhaps do a trial run on that machine. Thanks so much for the info, might be a while before I actually get these things in there.

 

[Phipli]

I ordered some up - I haven't remounted a chip before but I have a IIci that I think needs a similar removal and cleaning so I'll perhaps do a trial run on that machine. Thanks so much for the info, might be a while before I actually get these things in there.

You'll probably want to buy or borrow a hot air station if you don't have one. Something like this would be more than enough :

https://www.amazon.com/CO-Z-Soldering-Temperature-Desoldering-Electronics/dp/B01MR2IWBN/

 

[Phipli]

I still don't get the clearest sound out of the machine, looking to find some kind of music to play on there to test

Can you record the sound output on another computer (modern) and view the waveform in something like audacity?

Is it set to 8 or 16bit sound in the Sound control panel?

Sound Source :

PlayerPRO 4 - Macintosh Garden

The incredibly awesome PlayerPRO by Antoine Rosset. Version 4.5. PlayerPRO is a complete music editing program (SoundTracker). PlayerPRO can load and play many music (and sound) formats. Version 4.5 contains the awesome 'Screensaver' and 'Full View' video modes.

macintoshgarden.org

 

[jeremywork]

FWIW, I have a 640CD (DOS) which will begin to emit a strange static hum a handful of minutes after reaching the desktop. Oddly, starting the PC environment immediately ceases the sound, and both Mac and PC sound work properly.

The previous owner had the 'start PC when Mac is started' option checked and I discovered this caveat when I turned it off. I turned it back on and have had no issues with sound since.

constant staticy sounds out of the speaker when turned on

Not sure if 'when turned on' refers to immediately at power up, so your issue may be entirely different.

 

[superseth]

It happens right from boot for me, but maybe I have a more advanced form of whatever ails your machine. @jeremywork

 

[SpocksBeer]

In a similar boat with my LC630 DOS Compatible. Scratchy static noise, on and off, shortly after boot. Clears up when the DOS card is booted and the sound card is initialized. Given the lack of caps on the sound card, perhaps it's the opamps.

 

[Phipli]

In a similar boat with my LC630 DOS Compatible. Scratchy static noise, on and off, shortly after boot. Clears up when the DOS card is booted and the sound card is initialized. Given the lack of caps on the sound card, perhaps it's the opamps.

Does it go away if you remove the sound card from the DOS card?

 

[SpocksBeer]

I'll give that a try tomorrow

 

[Phipli]

I'll give that a try tomorrow

Sure thing. It's not too difficult. There is two screws holding the sound board in place and then it is just plugged into a connector, a bit like 90s powerbook RAM. If you have some, after your test without the sound board, squirt some contact cleaner on the connector pins just in case it helps.

Hidden side of the board for reference re the connector. Just pull upwards.

 

[SpocksBeer]

No worries at all - just wasn't going to do it right then as I'd only just stuffed everything back into the box and tucked it under the monitor!

Have pulled the DOS sound card, and yep, no static at all. Usually happens within the first few minutes, and has been running for about 10-15 so far with nothing. To be clear, you're suspecting an issue with the chips at u1 and u6, yes?

 

[Phipli]

To be clear, you're suspecting an issue with the chips at u1 and u6, yes?

They are the Op Amps yes.

Be aware your fault isn't identical to mine, I'm not saying "this is your fault with absolute certainty", but op amps can fail and cause noise, so it is a possibility and a fairly cheap fix if you have a hot air gun and can solder SOIC chips.

 

[SpocksBeer]

I do and I can, though I'm no expert. Looks like lots of potential for melty bits, so I'll have a think about this. Real pain of a board to diagnose since it has to be fully installed in the case to run.