Macintosh Plus Bang and Smoke

[Mikemike690]

I just brought a Macintosh Plus, took it apart to see the corrosion, with no damage luckily, and I decided to take the risk to start it up, anyway plugged it in and booted a disk and everything was fine, then after a couple seconds I hear quite a loud bang and smoke coming out of it. Does anyone know what causes this and how to fix it? Thanks.

 

[BadGoldEagle]

Looks like you have the same problem as this guy on Youtube.

Though could be any problem really. But any blown transistor/capacitor is lilkely to be the problem here.

Post a pic of the Analog board. You'll need a T15 driver to take the back case off. We'll tell you more once we have a look at the analog board.

If you know how to solder, then it's an easy and cheap fix. If you don't, you can order the new part and ask a repair shop in town to replace it for you.

 

[BadGoldEagle]

Where is the corrosion located? Sometimes the rear ports are corroded but most of the time they are okay. Just use very thin sand paper and they should look as good as new but now we've got that Analog Board problem to sort out. Don't worry. It happens sometimes and the machine was very well protected in case of power surges. Which I don't think is the case here since you shut it of immediately after you saw the smoke and heared the bang, right?

Oh by the way, was the screen working when this happened or was it completely dark?

 

[bibilit]

I don't have a Plus, but can be a problem with RIFA filter Capacitors

 

[Mikemike690]

Hi, just took a quick look at the board and it looks like one gold box thing has blown it's foil off. Here are some pictures, also I have very little soldiering skills. And here are the pictures of the gold box thing and some corrosion. Also would you know what the brown mark around the resistor would be? Doesn't exactly look corroded or anything. Thanks

http://imgur.com/mvsAy87

http://imgur.com/lWRLDVp

http://imgur.com/BLE7owR

http://imgur.com/d5i9yHy

 

[BadGoldEagle]

Okay. 

There you go. Blown RIFA filter capacitor. Interestingly enough only "international" boards have this cap. It's hard to find the info on the web since most Macs were sold in the US. If I had my Mac Plus on hand I could give you that information...but I can't do that now. Not until two weeks time.

Maybe you can still read what's on the blown cap, I think it is the same one as his little brother sitting next to him.

Once we know that, you can order the part on digikey (or the NZ equivalent, apparently you live in NZ right?) and then you have to find someone to desolder the dead one and replace it with the new one.

About that diode, it "looks" okay. Once you go higher the expected voltage the diode burns out and needs to be replaced. You picture shows that it was once hot in there. But not hot "enough" to kill it I think. But you should definitely check it with a multimeter, here is the specs of that diode. You can find information on how to test a diode on the web pretty easily. As for replacement, as this part was discontinued some time ago, this is the correct replacement as discussed on this thread

Good luck finding someone to do the job. When I introduced my SE/30 to a workshop in Paris, France, the guy thought I was still using it daily and suggested replacing it for a newer one. LOL

 

[uniserver]

you could just clip them off and continue to use the computer.  there will now be noise going back down the ac line... but

if you don't have a fancy circuit breaker it won't care.

 

[DragonKid]

US Mac analog boards use those RIFA caps as well.  Older ones like the 128k and 512k have one big Rifa PME271 type at reference C28, later model Plus boards use one of those smaller ones IIRC.  Most Apple II power supplies have them as well.  You don't hear about them exploding as frequently in the US, possibly because they are connected across the AC line and US line voltage is lower, but I still replace them if I see cracks in the plastic case since they're known to occasionally spray nasty sticky stuff that's a pain to clean off of PCBs when they go.  The replacement cap you use needs to be an "X2" rated safety capacitor intended for connecting across the AC line.