Mac Plus with no sound!

[Compgeke]

I've had a Mac Plus around here for a while that I built up into something useful from the remains of two non-working systems, and the one problem I have is I haven't any sound! Upon startup I just get static for a second, same when using headphones or speakers externally except light static remains. As far as I know this has no modifications except for a 4 MB ram upgrade, however I had no sound before I did the upgrade.

Here it is, doing a whole lotta nothing. It does work despite the obvious such as I haven't made a boot disk and I don't have a keyboard...

Here's a picture of the analog board, still in place:

And here's a picture of the motherboard:

I have a feeling the solution to my problem is going to be a recap, but I figured I would see if there's anything else I should check first.

 

[uniserver]

i can't quite tell if the resister is cut or not,

tried other ram?

that upgraded 2012 sticker is is probably the issue

 

[Compgeke]

That resistor is cut, and that 2012 sticker is something random I found tonight in a drawer. It did the exact same with the original 1 MB ram so I don't believe it to be bad ram.

 

[James1095]

Well the Plus doesn't use any SMT electrolytics, so while a re-cap may not be a terrible idea, it wouldn't be my first suspect here. I would look closely for bad solder joints or crud on the motherboard around the area of the sound chip and amplifier. IIRC the audio amp is on the motherboard and the analog board is just a passthrough to the speaker, but maybe somebody can correct me if I'm wrong.

 

[Compgeke]

From observation with a flash light (and 100W light right above) I didn't see any bad solder joints on the board. I did test capacitors and it appears that C7 and C14 read nothing while the others all read around 22 which is lower than the rated 33, but not enough that I would start really worrying about them as being the problem here.

 

[nvdeynde]

Replace the axial capacitors on the logic board. If that doesn't solve the sound problem, then the sound chip is probably gone and you're looking for a replacement logic board.

It can be the headphones jack too but I haven't seen them gone bad often. If you don't see any abvious corrosion on the jack, it's likely good but test it with a multimeter to make sure.

 

[nvdeynde]

It does look there's a wire soldered from the sound chip ( just under the serial number sticker ) to a resistor in the sound circuit. Looks like the board had sound issues in the past.... If the resistor still good ?

I have a parts Plus logic board here with a good sound chip: I can try to desolder it and for the price of postage it's yours.

 

[Compgeke]

That's just a trace that was brought out in the camera flash, not a soldered wire. I do have a feeling the sound chip is dead however, I re-soldered the connections for the sound chip and all I have now is a louder click when starting up so either there's a problem with the caps on the board or the sound chip has a problem. I'm leaning more towards sound chip problem, however I will replace the caps as soon as I find some, I know someone who might have a few.

 

[nvdeynde]

To exclude the speaker on the Analog board: do you have a spare 128K-Plus logic board around to test the speaker ?

Otherwise a multimeter meter will do as well to verify it's not shorted.

I have seen 1 logic board in my collection with a faulty speaker: it was shorted, as result the sound chip and a few resistors in the sound circuit were gone as well.

 

[uniserver]

That is interesting, might not of been something apple caught in R&D.

So if your speaker sounds funny at all, and you think the voice coil might be separating, you need to change that speaker asap...

Kinda like, change the breaks on your car, the first sign of a squeal, or else it just gets more expensive

 

[Compgeke]

Unfortunately this is the only compact mac I own, the other Macs are PowerPC desktop systems. At one point this system was working, as it had a different motherboard in that worked for a while then eventually developed the wonderful horizontal lines on the screen. I tried replacing ram, upgrading the ram and clipping the resistor, no go. At the same time I had another one with this motherboard on it that would turn on and you would only see a faint brownish flicker on the screen and it wouldn't do anything else. I pulled the motherboard from that one and the motherboard worked without sound, so that's what's in this system. I have no idea if the speaker worked on the other system, as

I wish I had that one with the bad motherboard and non-working analog board\CRT as I would love to have another for seeing if I can make it work. The problem with retrieving it is we were moving, the garage side door was left open by accident and I lost my dead Plus and a Performa 400 with a bad power supply, the stuff people steal today

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