Mac Classic Clicking Noise from Power Supply

[Steininger]

Been lurking on this forum to find answers to random questions I have ran into over the last few years. Finally I have a question I can't seem to find an answer to...

I was recently at my parents place for a visit and rummaging through the closet came across their old Mac Classic as well as a pile of floppies with one labeled "Neil's Ideas". Since I was about 7 when we got the computer back in '91 I am pretty curious what grand ideas that disk holds.

After plugging in the computer and turning it on there was nothing on the screen or noise from the fans but a faint clicking noise coming from the general area of the power supply. I did a bunch of research to see if I can find anyone describing a similar symptom but came up empty so I opened it up and found the battery on the motherboard had leaked.

I cleaned as much of the gunk as I could off and put it back together sans battery (i read that it should still boot without the batter, is that true?). Same result. Nothing on the screen and a faint clicking noise. Seems to come from the rear half of the board that the power supply is on. Cant seem to pinpoint exactly where. I ran it with the back case off and also noticed that the dust twitches in time with the click, not really sure what that means....

I finally got a reaction out of it after figuring all was lost and resorting to a firm slap to the side. After slapping it the fans spin up and the screen comes on with single pixel diagonal lines. There are faint noises from the HD but the computer never boots or gives a sad mac, ? disk, or any other sign of life.

Long story short what I am hoping to get out of the Mac Rumors best and brightest is what is wrong with the computer that would solve it by whacking the side? I assume hitting it is not a very good solution long term. Also what might be getting it stuck on the gray/diagonal line screen? I am guessing my battery sludge cleaning was less than adequate. I plan to run it through the dishwasher after dinner/dishes tonight as that seems to be a common suggestion online.

Another note, I do not have a keyboard cable so I just have the mouse plugged in not the keyboard.

Thanks all for any help!

 

[steve-p]

All I can offer is generic electronics advice that if giving it a whack somehow changes behaviour, you probably have a dry solder joint somewhere (which will likely be impossible to locate and fix without specialist help) or if you're lucky, a connector of some sort needs pulling, possibly cleaning and reconnecting. Or, if there are any chips that are not soldered to the board but are push-fit types, carefully easing them off and reseating them may help. The latter was a constant problem with the first Apple computer I developed for... the Apple II. Once a week the RAM chips needed pulling and reseating.

But... I don't like the sound of a clicking noise. It could simply be that the PSU is failing, I guess, assuming it's not coming from a hard disk (which usually indicates disk failure).

 

[MacTech68]

Steve-p's advice is very sound, but I'll go a little deeper.

The Power Supply is a switch mode power supply. By their very design, they will make a constant ticking/thumping sound when certain fault conditions occur. This protects the device they are connected to. There can be many reasons for it, but from what you describe, Steve-p is on the money. A cracked/dry solder joint is the likely cause. Sometime you can spot them visually (if you know what to look for). There is a chance that it's a cracked component or a faulty 5 volt adjust potentiometer.

I also believe that you have a second fault, being the motherboard. Not only have you had a leaked battery, but these boards have surface mounted electrolytic capacitors that leak too. Both of these leaks can corrode tracks which can cause the board to be non-functional. It is detailed and tedious work to replace the caps and find and repair tracks.

The lines you see on the screen are most likely what are called "retrace lines". They are about half an inch apart and run left to right at a slight angle. This would indicate that the screen electronics on the Power/Sweep board are fairly ok.

Cleaning the mother board in the dishwasher is a common solution but I would warn that it's only temporary and may not resolve the issue given that tracks can be etched clean thru by corrosion. If it DOES work, I'd consider it paramount to get the surface mounted electrolytic capacitors replaced as soon as possible.

 

[Steininger]

Thank you for the advice. It sounds somewhat unlikely that I will be able to get it fully functional with my skill-set but I will keep giving it a shot. Is there an easy way to tell if the electrolytic capacitor is leaking? I didn't see any obvious orange goo like there was around the battery.

 

[havokalien]

capacitors

I'm going to beat a dead horse.

pull the motherboard, i assure you the capacitors are toast, along with the battery on it.

Do a recap then worry about the power supply.

 

[MacTech68]

Thank you for the advice. It sounds somewhat unlikely that I will be able to get it fully functional with my skill-set but I will keep giving it a shot. Is there an easy way to tell if the electrolytic capacitor is leaking? I didn't see any obvious orange goo like there was around the battery.

BEFORE you wash the motherboard, check the board in good lighting at different angles. Leaked capacitors will have a "wet" area around them.

The capacitors in question look like this:

 

[Neoheurist]

Here's what it looks like....