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Macintosh II Will Not Power On.

reodraca

Active member
I was able to jumpstart it and get the arpeggio death chime, but then it suddenly switched off. No pop, no burning smell, no magic smoke, simply off. After that, no amount of jumpstarting the first pin of the power supply (white wire) will power the machine on.

I checked and there are no scorch marks on the logic board, and I cleaned and reseated the RAM, ROM, CPU, FPU, and MMU. This is the Rev. A board, so I don't have any electrolytic fluid eating at any traces, and both of the dead batteries aren't bloated at all.

I also checked the power supply and nothing is visibly wrong. The capacitors are reasonably unbloated, the fuses aren't burnt, and the transformers seem ok. I don't have a multimeter at present, so I can't check anything beyond my eyes.

Just wondering if any Mac II experts here can speculate as to whether the power supply up and died, or the logic board. I intend to replace both, but I've only found power supply replacements so far. I'd like to know which you'd recommend I replace first if I hypothetically had access to both.

Thank you in advance.
 

Juror22

Well-known member
Here is a link to an investigation of the II power circuit, I would get a cheap multimeter (borrow one?) and check the power supply/circuit, before I would throw in the towel and buy a new power supply or board. Although if someone here offers you a good deal on one, take it.

If you could get a known-working power supply (recapped if possible) I would get that first, since any trouble-shooting on the board would sort of assume good power.
 

reodraca

Active member
Here is a link to an investigation of the II power circuit, I would get a cheap multimeter (borrow one?) and check the power supply/circuit, before I would throw in the towel and buy a new power supply or board. Although if someone here offers you a good deal on one, take it.

If you could get a known-working power supply (recapped if possible) I would get that first, since any trouble-shooting on the board would sort of assume good power.
Ooook, so I think for now I'm going to skip checking this power supply and go for a new one. You won't believe what just shook out of it: A plastic guitar pick. Not sure if it can cause a problem, but I'm not taking any chances. It might've rattled around for literal decades and broken any number of solder joints and wires. I can't tell, but I think I'd rather play it safe.

This was probably at a university for at least 20 years of its life, according to the sticker in the back, so it probably saw some abuse before it ended up in the home of the person who sold it to me. Who knows what sort of carelessness it saw?
 

Unknown_K

Well-known member
Plastic is non conductive so the guitar pick probably didn't hurt anything.

Fuses can blow without burning if they are fast acting, you wouldn't notice without a multimeter.

While axial capacitors don't leak, they can dry up inside and quit working without bloating. Luckily for those you can easily desolder one end and check them with a cheap Chinese ESR meter.

https://www.ebay.com/itm/403342352472?

Replacing a 30 year old PS with another 30 year old PS without getting a multimeter and checking out the circuit is probably going to be expensive. I mean you can replace everything 5 times over and not get a working system.

Good luck.
 

reodraca

Active member
Plastic is non conductive so the guitar pick probably didn't hurt anything.

Fuses can blow without burning if they are fast acting, you wouldn't notice without a multimeter.

While axial capacitors don't leak, they can dry up inside and quit working without bloating. Luckily for those you can easily desolder one end and check them with a cheap Chinese ESR meter.

https://www.ebay.com/itm/403342352472?

Replacing a 30 year old PS with another 30 year old PS without getting a multimeter and checking out the circuit is probably going to be expensive. I mean you can replace everything 5 times over and not get a working system.

Good luck.
You make some excellent points. Thank you for the links. I suppose I'll be getting a multimeter, then.

My issue is that I don't have experience with soldering not the money to get a decent iron. I came across this Mac II as a gift, or I definitely wouldn't have it to work on. I know retro computing is an expensive habit. I really need an iron.
 

jajan547

Well-known member
You make some excellent points. Thank you for the links. I suppose I'll be getting a multimeter, then.

My issue is that I don't have experience with soldering not the money to get a decent iron. I came across this Mac II as a gift, or I definitely wouldn't have it to work on. I know retro computing is an expensive habit. I really need an iron.
Cheap soldering iron, solder, and solder wick will run you $45-$60 and new capacitors probably another $10
 

reodraca

Active member
Nice! See @reodraca you can do it, if something is broken you only make it more broken at worst so why not give something a try and maybe learn something along the way, or even fix it altogether.
I had honestly thought I'd be paying a lot more. And yes, the desire to learn soldering has always been present.
 

jajan547

Well-known member
Thank you. I really hope there's continuity, because as someone who's just about to learn soldering, I am definitely not prepared to run wires on the back of the board to replace the trace.
Not nearly as abad as it sounds and invest in flux will make things easier for you.
 
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