No sound on Mac 128k

[Patrick]

Picked up a 128k recently. Had a sad Mac that indicated bad ram. Not understanding the address correctly I decided to replace 8 Ram chips. After that, I then realized that the error code was indicating 2 ram chips were dead. So I replaced just those 2 (totaling 10 ram chips replaced) and the Mac boots!

However, no beep. also booted to finder and the volume in control panel doesn't produce any beeps. I have narrowed the problem down to the logic board as I tried it in a 512k analog board that does work. I also put the 512k logic board on the 128k analog board and it beeps. That is, the symptom of no beeps followed the logic board.
the Mac seems to work otherwise.

Anybody know what I can look for? I noticed the headphone jack is VERY corroded.

 

[Branchus]

Have you tried using headphones? If so, do you get any sound from them?

 

[Stephen]

Have you tried using headphones? If so, do you get any sound from them?

Exactly this. For some reason, I often find older macs have dead speakers (with no obvious sign of damage). I have a “new to me” 512k with this problem right now.

 

[Patrick]

Yes, I've tried both headphones and speakers. The headphone jack has a little window on it. and its very red that looks like rust on the inside. ... I don't know if that would cause sound to not work through the speaker on the analog board?

I was also trying to say that the speaker works as I tested it on a 512k logic board.
Thats to say between a 128k and a 512k. everything works interchangeably . except the 128k logic board never has any sound.

 

[Elemenoh]

All that rust has likely created a connection as if headphones were plugged in. Try replacing or even just removing the rusty connector and your speaker will probably start working.

 

[Stephen]

Yes, I've tried both headphones and speakers. The headphone jack has a little window on it. and its very red that looks like rust on the inside. ... I don't know if that would cause sound to not work through the speaker on the analog board?

I was also trying to say that the speaker works as I tested it on a 512k logic board.
Thats to say between a 128k and a 512k. everything works interchangeably . except the 128k logic board never has any sound.

Interesting, I see. I don't think there's any harm in cleaning the headphone jack (or outright removing it for testing purposes). If you're open to a little fringe experimentation you could connect a speaker directly to the connector on the logic board.

edit: for clarification, the red circle indicates the orientation of the logic board plug and the green circle is the speaker "positive".

 

[Patrick]

So I tried to remove the headphone jack before and failed. However, I tried it again today and it didn't seem that hard. Perhaps I cleaned the vacuum gun and it performed better. or maybe some fresh solder helped?

anyways. headphone jack removed. and I cleaned up the little bit of corrosion that was on the board. Still no beep. On the plus side, computer still boots into finder with floppyemu. (I'm mostly still excited when I don't make things worse when trying to restore computers)

I don't have a speaker handy to try. I'll try to acquire one and test it out.

 

[Stephen]

This lousy scribble is the schematics for the speaker driver, I believe @JDW may have better schematics but I am not sure.

Source

 

[JDW]

So I tried to remove the headphone jack before and failed. However, I tried it again today and it didn't seem that hard. Perhaps I cleaned the vacuum gun and it performed better. or maybe some fresh solder helped?

anyways. headphone jack removed. and I cleaned up the little bit of corrosion that was on the board. Still no beep. On the plus side, computer still boots into finder with floppyemu. (I'm mostly still excited when I don't make things worse when trying to restore computers)

I don't have a speaker handy to try. I'll try to acquire one and test it out.

You will need to start checking voltages with a digital multi-meter on the audio circuitry to see which components could be bad or which traces may be severed. I will send you a PM with high quality schematic for the 128K motherboard.

 

[Patrick]

Thanks everybody. It looks like I'll have to bust out the multimeter and test things as was suggested. ... and figure out how to do that safely while the board is both on and flat on teh table. (an extension cable somehow for the yoke)

But for now I think I may focus on other projects that are lower hanging fruit for me. I still have plenty of caps to replace and so on. I'll report back on this thread if i get it working.

 

[max1zzz]

With the headphone socket removed your going to need to jump pins 1 and 2 on the headphone socket or you'll get no audio, there is a normaly closed switch between those pins that disconnects the internal speaker when headphones are plugged in

 

[Patrick]

Thanks for that!
umm ....

Which is pin 1 and which is pin 2? (maybe just tell me what pin 3 is and i can deduce which is pin 1 an 2)

Either i got it wrong in my guess. .. or i still have more troubleshooting to do.

 

[max1zzz]

I don't have one of these boards to hand to check but looking at the schematic it looks like pin 3 should be connected to ground so if you find which one is grounded and jump the other two you should be good

 

[Patrick]

The pin that is nearest the edge doesn't have any traces on either side. that i can see. So i think thats the ground pin. i jumped the other two. Still no sound. so problem is prolly someplace else.