Mac Plus analog board replacement

[Kallikak]

I just had a fairly catastrophic failure of my Mac Plus analog board. A few components are seriously charred, and though I haven't removed the board yet to check over thoroughly (it's too late at night to start doing this properly), I expect there will be too much damage for anything other than a replacement. A disturbing aspect is that this failure occurred while the machine was turned off... I had used it about an hour earlier, turned it off, but left it plugged in. Next thing I know is that the magic smoke has escaped from the Plus and filled up the living room. (My wife was not particularly impressed...)

Anyway, I have a 512K, a 512Ke and a Classic spare. I am hoping the Classic analog board is compatible, since that is an entirely spare parts machine, and also the most recent. Does anyone have details handy on the compatibility or otherwise of the Classic analog board with a Plus?

Thanks,

Ken

 

[Scott Baret]

The Classic and Plus analogs are not interchangeable.

Analog boards that are "common designs" include:

128K/512K/Plus

SE and SE/30

Classic/Classic II (Revision A)

Classic/Classic II (Revision B)

(see my FAQ in the Compact Macs forum for more information about Revision A and Revision B)

If you want a new analog board, look for a pull from a Platinum Plus as they have more reliable power supplies than their beige predecessors.

 

[Mac128]

The Classic and Plus analogs are not interchangeable.
Analog boards that are "common designs" include:

You seem to be saying they are both not interchangeable and compatible.

However, what I think you are saying is that there may be a CRT compatibility issue. In which case, take the Classic's "B" board compatible CRT with the analogue board to the Plus.

Since I have successfully powered all of the compact Mac logicboards with every other analogue board in some misguided experiment I was obsessed with, I will tell you that they are all interchangeable and will all fit within each other's cases. What is required in all cross-model utilization is a modified pin-connector cable, which is easily done by extracting the pin connectors from the plastic headers and inserting them into the proper order of the other Macs analogue connector. Keep in mind, the SE modifies its sound connection which requires additional configuration. Also, the Classic has software brightness only which is not implemented in other logic boards, so the Classic is not the best analogue board to use with earlier compacts for this reason (though I have never reduced the default brightness level on a Classic, if only because it was so difficult). This all works because the interconnect principle is identical on all of the compacts (excluding the CCs). The usual disclaimers apply ... I did not keep the logic boards connected in this fashion for any length of time, so long term result may vary.

That said, the board may be in better condition than you think. Perhaps Tom Lee can lend some insight as to why it chose to fry itself after it was powered off, though. Wile replacement may be the easiest, the time is coming where the working supply of replacement parts is in need replenishment, meaning this army should endeavor to repair rather than replace as much as possible.

 

[tomlee59]

He probably means that, on a given line of his list, those items are compatible with each other. However, items on one line are not (necessarily) compatible with any on another line.

As to why you got smoke with the switch off, that's extremely unusual. It takes a multiple-element failure for that to happen. The probability isn't zero, but it's small. This might be a good time to play the lottery.

It's hard to say for certain what happened without examining the debris, but it could be that the switch failed in a high-resistance state, so that "off" was actually "high resistance." That could've heated up the switch to the point where it cooked itself, and its environs.

 

[Dennis Nedry]

I think a picture of your burned analog board is in order if you can, Kallikak, this is making me quite curious. The only thing I can think of is what tomlee59 said, maybe the switch failed somehow or was left at the perfect spot between off and on where it proceeded to burn up. You can do this to burn up ordinary light switches if you're careful and persistent, and it does produce quite a burning stench. All depending on how many lights, etc. are hooked up to it. 60W won't do much, but 600W, well now we're talking.

 

[Kallikak]

OK - it's taken me until today to give this more attention. To keep things going I just swapped the Plus motherboard and back case with my 512Ke.

Here are a couple of pics of the analog board. Clearly the damage is quite extensive.

http://school.anhb.uwa.edu.au/personalpages/kwessen/Home/PlusAnalog1.jpg

http://school.anhb.uwa.edu.au/personalpages/kwessen/Home/PlusAnalog2.jpg

Ken

 

[wally]

If the international version is wired similar to the US version, parts of the line filter BEYOND the fuse but before the switch appear to have incinerated, possibly also charing the epoxy board enough to make it conductive carbon also. W12 is removed, as it should be for 240V mode. A lot of design review, special certified parts selection and final product safety certification is supposed to assure this NOT happening due to AC line connected component failure. It sometimes happens that parts fail in such a manner that they draw enough current to overheat, but not enough to blow fuses or circuit breakers. The metallized capacitors in the filter are supposed to self heal in case of internal shorts and not overheat. The filter inductors have stringent insulation and air gap requirements to make shorts and overheating very unlikely. I'm curious...what actual current rating is stamped on the fuse, and did it blow or melt? Did any other appliances or light bulbs fail shortly thereafter indicating a possible lightning strike?

 

[Kallikak]

The fuse is rated 1.6A/250V and has blown. There was no storm or other problem. The board is certainly charred - but only after I remove the dodgy components and clean it up will I be able to see the full extent of the damage.

Ken