Mac Plus Faint "Click Click" Sound from Analog Board

[AndyDiags]

A couple of my Mac Plus's make this very faint click click sound. Has anyone ever had the same and figured out what it could be?

-It's coming from the lower center half of the analog board
-Sounds like small electric shocks
-With lights off, no visible arc or spark is seen
-Board has been recapped and voltages adjusted
-Same sound pattern occurs on multiple units
-Starts happening right after when the disk/mac logo appears on screen
-Doesn't occur if floppy drive is disconnected
-Noise stops if I put a disk in the floppy (either on boot screen or while in OS)

 

[Alf Torp]

Sounds like arcing. Could be a bad cap or an almost short in a high voltage area. Just a guess based on your clip.

 

[Daniel Hansen]

Do the machines operate normally otherwise? Some Pluses do this, I believe it's dependent on the drive installed. It's considered normal operation and nothing to worry about ---- is the drive installed a MFD-51W-03?

 

[AndyDiags]

Had some extra time to investigate more today.

Took a Mac Plus apart and laid it out flat so that it's easier to isolate where the sound is coming from, as shown above.

The clicking is coming from the transformer (part # Astec 01820 157-0025-A). However due to the electrical interference generated by the transformer, it gets picked up and amplified by the speaker right next to it.

Here's a video of me disconnecting and reconnecting the speaker while system is running. You'll need to turn your volume all the way up to hear it. When disconnected, you hear a very faint click, once I connect the speaker the clicking can be heard very easily.

Another thing I noticed is that all 6 Mac Pluses I have make this sound from the transformer, and some of these have different brand transformers. Not all of them, however, get the interference picked up and amplified by the speaker.

So in conclusion, Sony 800k drives cause the transformer to generate very faint arcs, but this is normal as all Mac Pluses do it. In a couple of my systems, the interference is being picked up by the speaker and that's unexpected.

 

[Mu0n]

My Plus also has that sound.

 

[RetroTheory]

From the Dead Mac Scrolls lol

 

[AndyDiags]

From the Dead Mac Scrolls lol

Thank you! I checked the book before but somehow completely missed it!

Interestingly enough, it says "or replace the disk drive". It's semi-suggesting that replacing the drive may fix the sound? All my floppies have already been re-capped, so not sure how a new drive may help with the ticking. Perhaps a newer floppy drive board revision addressed this issue. Definitely not going back again to see which of my Macintoshes has the newest floppy rev to see if it helps with this issue.

 

[Mu0n]

could you place the speaker farther to reduce the interference? or is it something that happens as a noise in the voltage picked up by it?

 

[Daniel Hansen]

Interestingly enough, it says "or replace the disk drive". It's semi-suggesting that replacing the drive may fix the sound?

I think this leads from the observation that the red-labeled drive (MFD-51W-x) has this issue but the black-labeled drive (MP-F51W-x) does not. In other words, it probably should say "replace the drive with something other than MFD-51W-03."

I haven't tested this myself, just going off what others have said (including Pina).