Macintosh Classic II with no sound. Analog board issue?

[jimbojones]

I have a Mac Classic II that has no sound. I recapped the logic board but no luck. However, I tried the board in my Mac Classic and the sound came straight on!

My question is, does the analog board have anything to do with generating sound (is it an amp)? And if so, is it likely to be the caps on that?

Anything else I could try?

Just asking before I dismantle it all as removing the tube and analog board is a bit of a longer job

 

[ymk]

There's no active audio circuitry on the analog board.  The speaker runs straight to the logic board connector.

 

[karrots]

I had a similar thing with my CII sound was intermittent. I ended up removing the sound chip cleaning and resoldering to solve it.

 

[bibilit]

If you have got sound with another AB, issue is on the CII AB board.

Faulty speaker ??

 

[jimbojones]

Thanks everyone. Good to know about the lack of audio circuitry on the analog board. Will check out the speaker!

(I tried the Classic logic board in the Classic II case and no sound either, so am sure it's not the logic board).

 

[jimbojones]

Does anyone have a pinout of the logic board to analog board connector on the Classic II?

 

[Andy]

The Classic and Classic II use the same right? I found this on page 18 of the Classic 1 dev note:

https://cdn.preterhuman.net/texts/computing/apple_hardware_devnotes/Mac Classic.pdf

Pin number      Signal Signal       Description
1               +12V                +12 volts
2               +5V                 +5 volts
3               +5V                 +5 volts
4               /VSYNC              Vertical synchronization
5               /HSYNC              Horizontal synchronization
6               VIDOUT              Video output
7               SND                 Sound signal
8               –12V                –12 volts
9               PWM                 Brightness control signal
10              GND                 Ground
11              GND                 Ground
12              GND                 Ground
13              GND                 Ground
14              GND                 Ground

Are you getting anything on the line out port?

 

[elemenoh]

I had the same problem. The voice coil of the speaker itself was broken. It should read around 60 ohms with a multimeter. After swapping the speaker sound worked fine. It’s a bit of a pain to swap because there are metal rivets holding it in place. I used needle nose pliers to smush them on the top side of the board and wiggle them out from the bottom side. I used some cut rubber as posts to hold the speaker in place and hot glue on top to secure them a bit better. 

 

[iJol]

I had a similar thing with my CII sound was intermittent. I ended up removing the sound chip cleaning and resoldering to solve it.

Which one is the sound chip? The U1 (MC34119) or U4 (DFAC)? I don't get sound on my Classic II after cleaning and recapping the Logic and Analog Board. Checked the traces already, the seem fine. External speakers doesn't work, too.

Edit: okay, looking further on Google and it seems to be the DFAC.. Looks good, no corrosion or something like that, but I'm gonna to desolder it tomorrow and check if there's some cap juice underneath..

 

[Mr_formal]

I had the same problem. The voice coil of the speaker itself was broken. It should read around 60 ohms with a multimeter. After swapping the speaker sound worked fine. It’s a bit of a pain to swap because there are metal rivets holding it in place. I used needle nose pliers to smush them on the top side of the board and wiggle them out from the bottom side. I used some cut rubber as posts to hold the speaker in place and hot glue on top to secure them a bit better.

Hey what speaker replacement did you use? I have no audio on my classic II, and I'm looking for the right replacement speaker. I was also wondering if classic speaker is supposed to be magnetic, as mine is not.

 

[chrisdaun]

Hey what speaker replacement did you use? I have no audio on my classic II, and I'm looking for the right replacement speaker. I was also wondering if classic speaker is supposed to be magnetic, as mine is not.

My classic II speaker was dead too. I replaced mine with one from a Macintosh SE. The ohm ratings printed on the back of both speakers were the same so I drilled out the rivets on the classic II speaker and replaced with the SE speaker

 

[chrisdaun]

Here you can see the value. This is a picture from the original speaker

 

[Mr_formal]

Here you can see the value. This is a picture from the original speaker
View attachment 59488

Thanks that helps a lot, I managed to recap both boards, grease up the floppy drive, even was able to repair the HDD, but the speaker was the hardest part to figure out for some reason. I looked at other forums and it says there might be a switch at the back of the line out jack that's stopping the speaker from working, and I figured I might check that first. My multimeter reads 59.9 ohms on the speaker, so it looks like it's in good order. I'll order SE speaker if I can't get it to work.

 

[chrisdaun]

The ohms you are seeing on the meter make be believe the speaker is good too.
Mine was open circuit so defiantly bad.

Test continuity from the speaker back to the board on both wires to rule out a broken wire to the speaker.

 

[Mr_formal]

I tested continuity from the logic board to analog board to speaker and it was fine. I tested to see if anything shows up on line out pin when Mac is turned on but nothing shows up.I checked the switch on the 3.5mm jack and it was stuck, but moving it to the right position didn't do anything, I also plugged in external speakers, but those didn't work either. Could it be sound chip?

 

[chrisdaun]

Possibly
Can you bypass the switch in the headphone jack with a jumper wire?
Maybe the port is just shot or corroded inside.
I think you would need a scope to properly diagnose the sound chip. Above my level of knowledge.

 

[Mr_formal]

I checked continuity of the switch and it was fine, I'll try to jump it tomorrow, hopefully it's not the sound chip, I wouldn't know how to diagnose it either.

 

[Mr_formal]

I managed to submerge the jack in vinegar, and cleaned up the corrosion. The switch has perfect continuity, but still no audio out of internal and external speakers.

 

[Mr_formal]

I tested out shorting the pins on the audio jack today, but that also didn't work. It actually corrupted the picture shorting those pins. I was wondering if you could test your speaker to see if it is magnetic, mine isn't and I think that might be an issue. Metal doesn't attract to the back of my speaker, and I think it's supposed to.

 

[zigzagjoe]

It's got a shielded magnet. No attraction is normal. To test the speaker, you could take an AA battery, connect one side to ground, and momentarily connect positive to the sound pin on the lb connector (disconnect lb first) mentioned above. The speaker should crackle which means it's fine.

You may have tested this already, but connect headphones and boot to see if you hear a bong in those.

Check the voltage on -12v at the LB when machine is running. If it uses a similar audio amp setup to the SE 30 it needs both 12 and -12 for proper audio operation.