Headless trayloader iMac - audio issues - faulty board?

[croissantking]

I'm currently running a Rev. A Bondi Blue iMac setup externally with an ATX PSU.

It works, but I've had some teething problems with this setup:

- No sound output from the headphone jack
- System slows to a crawl or hangs at random times; or doesn't boot.



Through trial and error I've found both issues are related to the sound circuitry. In particular, any time I'm having a slowdown or hang, making physical contact with the sound chip gets things unstuck. This is repeatable and verifiable behaviour.

To be specific, I am brushing my finger up against the red highlighted pins, not putting any pressure on them at all – therefore introducing a bit of capacitance.

I have a hunch it may be specifically pins 62 and 63 (SPKRR and SPKRL repectively) that are the ones that need tickling. I say this because 1/ I have no sound output on the headphone jack and 2/ I'm missing the proper harnesses and speakers that an iMac enclosure would normally have - and maybe the circuitry doesn't like that.




To anyone who's run an iMac headless like this, have you seen this issue?

Tagging @LightBulbFun

 

[croissantking]

making physical contact with the sound chip gets things unstuck. This is repeatable and verifiable behaviour.

To be specific, I am brushing my finger up against the red highlighted pins, not putting any pressure on them at all – therefore introducing a bit of capacitance.

Using some kapton tape, I've isolated the pin to #58 RESET (connected to BURG RST5V L). So, it seems like the chip is not coming out of reset properly?

 

[CC_333]

I remember reading an article years ago about an iMac ATX conversion that was hacked into a Mac II enclosure.

Do you have similar plans (putting the thing into a pretty and tidy box, basically) or do you intend to leave it bare for testing and experimentation?

c

 

[croissantking]

I remember reading an article years ago about an iMac ATX conversion that was hacked into a Mac II enclosure.

Do you have similar plans (putting the thing into a pretty and tidy box, basically) or do you intend to leave it bare for testing and experimentation?

c

I’m not sure yet - probably not but it’s a cool idea. Wouldn’t an LC-style case be perfect?

 

[CC_333]

I’m not sure yet - probably not but it’s a cool idea. Wouldn’t an LC-style case be perfect?

It would be!

When that article was written (not sure when, but probably early-mid 2000s), 3D printing wasn't available, but now it is, so a custom LC-style case could conceivably be created from scratch without sacrificing an existing machine, as the writer of the article did.

I don't have the resources to do it, but I'm sure someone around here does.

c

 

[LightBulbFun]

I'm currently running a Rev. A Bondi Blue iMac setup externally with an ATX PSU.

It works, but I've had some teething problems with this setup:

- No sound output from the headphone jack
- System slows to a crawl or hangs at random times; or doesn't boot.

View attachment 93077

Through trial and error I've found both issues are related to the sound circuitry. In particular, any time I'm having a slowdown or hang, making physical contact with the sound chip gets things unstuck. This is repeatable and verifiable behaviour.

To be specific, I am brushing my finger up against the red highlighted pins, not putting any pressure on them at all – therefore introducing a bit of capacitance.

I have a hunch it may be specifically pins 62 and 63 (SPKRR and SPKRL repectively) that are the ones that need tickling. I say this because 1/ I have no sound output on the headphone jack and 2/ I'm missing the proper harnesses and speakers that an iMac enclosure would normally have - and maybe the circuitry doesn't like that.


View attachment 93078

To anyone who's run an iMac headless like this, have you seen this issue?

Tagging @LightBulbFun

Whoops, missed the tag somehow,

I admit I have not run my headless iMonster for very long (because theres no fan cooling the CPU) but I have put it through quite a few boot cycles n things like that, and its been shockingly reliable, never had much in the way of issues with it all

my board and CPU card is a Rev D 333Mhz one


but I have never actually tried the Audio output on it, so cant say if that works or not

 

[croissantking]

Whoops, missed the tag somehow,

I admit I have not run my headless iMonster for very long (because theres no fan cooling the CPU) but I have put it through quite a few boot cycles n things like that, and its been shockingly reliable, never had much in the way of issues with it all

Mine is very reliable as well, except for the one issue I described...

my board and CPU card is a Rev D 333Mhz one


but I have never actually tried the Audio output on it, so cant say if that works or not

If you wouldn't mind, next time you boot it up, plug some headphones in and see if you can hear anything.