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Silent 700 Model 765: are these things cursed?

ClassicHasClass

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Mar 22, 2013
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This is the famous "bubble memory" unit (it's an ASR, but instead of tape, it uses bubble memory). I managed to land three. Two of them have apparently bad lower boards (the one with the 9980), per the maintenance manual based on its symptoms of going into COMMAND mode and refusing to exit. The third had a bad printer mechanism, so I replaced that. It briefly worked but while I had it powered up the lower board on that died too! (Eventually the upper board died as well, but I took one from the others which seems to work.)

It seems like the lower board is a common flaw on these machines, which because it drives the upper board with the 8080, makes the unit useless without it. Unfortunately the lower board is unique to the 760 series, and the maintenance manual does not go into component-level repair. (If anyone breezily suggests capacitors without any other consideration, I will find you and strangle you, even though it's possible.)

Does anyone have any experience with these? My 745 works great so far, so I think it's something about these units in particular. But I love the bubble memory feature and I'd love it to live again. In related news, I have a crapload of bubble memory boards now ...
 
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