128/512k, Plus, SE, Classic Analogue Boards Compatibility?

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Joined: Mar 12 2005
Posts: 117

This sounds like a hack, but really it's a compatibility question. According to prevailing thought, the 128k through Plus all suffered from bad analogue board design, which the Plus tried to correct with more robust parts by the time it finished its production run making it the most stable of them all, but still flawed and prone to eventual failure of certain parts.

Now, the inevitable happened: my 128k flyback transformer died. So here's the dilemma, start the slow part replacement process on the analogue board, piece by piece, or sacrifice authenticity of the 128k and simply put in an entirely new analogue board which should last intact for many more years to come? More about authenticity later.

Let's say I'm going to put the analogue board from a MacPlus into my 128k. That should work fine with minimal adjustments, but no "hacking". But why not an SE analogue board, or even a Classic (don't know enough about the Classic yet). But according to Larry Pina's book, it's the same form factor and there is really only one major difference in terms of how they work: the vertical video circuitry. Otherwise, Apple fixed most every problem they had with the original 128k form factor analogue board, so wouldn't this be the best board to use (I assume the Classic went even further, but not sure about compatibility). Even if the video circuitry on the SE was substantially changed, isn't that internal to the analogue board?

AUTHENTICITY: I wish I had my original 128k, boxes, manuals disk, etc. in a pristine condition. But it's been used for many years and I guess I should count myself lucky that it lasted this long without any repairs -- and I probably brought this on myself by putting an upgraded 128k board to 512k I bought off eBay. But, if you are going to use any of these old Macs, things are going to go wrong inside them because of inherent design flaws and age. So what do you do? Anything you replace or upgrade inside them immediately taints the originality once you remove that first solder. If you replace it with an original part, scavenged from another period Mac, or from an online source -- you simply risk unpredictable failure again as these parts were admittedly under-spec-ed for their use. If you replace it with an improved part, then you've automatically compromised the authenticity. So, if you compromise just one part, why not the whole bag of tricks (i.e. the whole analogue board). if the goal is to make it truly functional. If you replace it with an original part, at least you're staying true to the original manufacture, but you risk the machine crapping out at the worst possible moment (like when you trot it out at a computer convention for show & tell).

What to do?

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dankephoto's picture
Joined: Dec 20 2003
Posts: 1900
use a Plus AB, stash 128K AB

you're trying to have your cake and eat it too, it's not simple to get a 128K/512K AB up to a reasonable level of reliability without compromising its "authenticity".

My solution is to separately keep the failed original part (intact) but for actual usage replace it with a working part (in this case, a Plus AB.) For demos and such, who cares if the AB isn't strictly original, eh?

As for using an SE/SE30 AB in a gen 1 Mac . . . never seen it done, but that don't mean it hasn't been. Just seems like a lot of bother when working Plus boards are still relatively plentiful.

You might want to keep your eye out for a period case fan, they apparently were quite effective at preventing AB failures. Ooops!, another fan isn't what you were wanting? Cool Mac

dan k


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Joined: Dec 20 2003
Posts: 361
Using an SE analogue board wo

Using an SE analogue board would involve considerable hacking.
What I did to maintain a degree of originallity was look for a 128/512 that had the Mac Plus upgrade and used the analog board from it.
They're easy to identify, any Mac Pluses that don't have Macintosh Plus on the front were 128/512k macs that were upgraded to Mac Plus.