Mac Plus clicking/ticking noise - works fine

[unity]

I am working on some Mac Plus models and each one makes a light ticking noise but only when the "?" icon is up. Not before that, not during boot or after boot as it idles on the desktop. The noise is coming from the analog board for sure. Its not loud. If I disconnect the internal floppy, it stops. These are all 800k systems and all four work normally.

Motherboard voltages are all good taken at external floppy port.

Is this something I just never noticed before? Or are they ALL suffering from the same issue?

 

[techknight]

its likely digital noise your hearing backfeeding into the power supply. good caps usually filter that out. bad ones, not so much. 

 

[unity]

Well I have gone through six boards, all the same. Floppy disconnected, no issue. Just cant boot then! I even dove into some 512k power boards.

 

[techknight]

Odd, Well the floppy drive does pull a bit of current, and so does an HDD but those machines dont have one. 

Dont forget the FDDs have caps too. You can try a known good FDHD drive or something and see if the sound goes away? eliminate all possibilities. 

 

[unity]

Well each machine I am trying is with a different 800k drive and usually a different mobo.

Very odd. Maybe I should check the house voltage. We are in the middle of a massive blizzard.

 

[techknight]

Ouch. it was around 70 here... 

 

[Elfen]

If it were the Sony Floppies used in the LC 475 series, LC IIIb or pre-PowerPC with the black swinging door, I would say that its the caps. Next to the head stepper motor are two caps that are the same type of the logic board that leaks.

But the Plus uses the older 800K drives. There are 2 caps by the head rails but they are tiny and I would not know if these leak.

 

[K55]

If anyone in the future reads this, you can also have a problem with older analog boards 128k -> plus era macs wherein you plug the power into a GFCI outlet.

This will cause the transformer to have a little flyback, and you'll start to hear clicking (not good :-/ ). So just a note, old mac = no GFCI.

 

[olePigeon]

Sounds like we found the answer?

 

[unity]

Well it was indeed pugged into a GFCI! Of course, they ALL were so that explains a lot.

So not good in what way exactly? Short term, long term, etc.  And thanks K55!!!

 

[K55]

Well you can think of a transformer as basically 2 inductors/coils back to back in a ratio that turns one voltage into another.

A basic rule of an inductor is that Vout=L*di/dt, or that basically when there's a rapid change in current you get a big ass spike in voltage

(sometimes in the KV range!!!) .

This voltage spike is heard as a clicking noise in the transformer, as it arcs between the coils.

This is bad because it can fuse the coils and mess up the windings.

Now normally this spiking shouldn't happen (due to having smoothing capacitors, diodes etc), but lets say that when the mac turns on,

there's a large amount of current drawn into the device to turn on the CRT.

So what I'm guessing/musing that occurs is the GFCI partially "trips" the internal breaker but catches itself,

but then this creates a feedback loop where the GFCI turns on, this spikes the transformer (aka the click sound), the GFCI does its thing and

this keeps repeating.

I haven't seen this problem with any mac SE and up so its probably a design issue with the 128k -> plus analog boards.

 

[unity]

What is sooooo weird, to me and maybe you can explain...  Why is it only when the "?" icon is up does this happen. I will re-cap the issue. It does not happen on any of the ones I tested (I think almost a dozen total) until this icon appears. So the CRT is on, there is a grey pattern generated by ROM. But only when the flashing disk icon is up. Then when I insert a floppy, its stops. It can sit idle at the desktop for as long as I leave it and still nothing. Brightness of display has no effect. And to boot, if I disconnect the internal floppy drive it it will not do it at all during the flashing icon - of course I cant boot it now.

Thats the part that really throws me for a loop. And I can do the above with any of the twelve or so I painstakingly tested.

Now if it did it ALL the time we can say its annoying and a bad thing and we can be happy with it being the GFCI. But it is the GFCI since I tested on again two ways, on and off GFCI. No ticking on a normal outlet.

 

[K55]

If it were the Sony Floppies used in the LC 475 series, LC IIIb or pre-PowerPC with the black swinging door, I would say that its the caps. Next to the head stepper motor are two caps that are the same type of the logic board that leaks.

But the Plus uses the older 800K drives. There are 2 caps by the head rails but they are tiny and I would not know if these leak.

@unity Well if the problem stopped when you unplugged the floppy it's most likely the floppy drive then, maybe a loading issue or a mismatch in impedance, its hard to tell from a brief look at the schematics.

I'll see this weekend if I can get an oscilloscope and probe the AC,5v,12v line to see if there are any spikes.

 

[olePigeon]

If you find the source, could it be remedied by soldering a few resistors or capacitors or something?  (I don't know anything.)

 

[unity]

Well it could be the floppy, maybe. Uniserver said there was something in the Dead Mac Scrolls that mentions the 800k drive tick. But I found nothing. Just weird they dont do it on a normal outlet. So maybe it a combo with the 800k drive and GFCI.

 

[techknight]

Who cares as long as everything works? 

 

[bigmessowires]

My Mac Plus does the exact same thing. I think every time the Mac polls the drive to see if a disk was inserted, it makes that ticking sound. I don't really understand it.

 

[unity]

Who cares as long as everything works? 

I care.

 

[Paralel]

Mine does it as well, I usually just shove a disk in and boot it. I never paid much attention to it.