LisaList2
General Category => LisaList2 => Topic started by: stepleton on October 03, 2022, 04:32:12 pm
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I've been trying to offer some repair suggestions to a person on vcfed who's repairing a damaged I/O board (https://forum.vcfed.org/index.php?threads/apple-lisa-2-a6s0200-is-this-fixable.1240114). This time it's not the battery whodunit --- the board is from a 2/10. Instead, somebody ripped off a whole bunch of ICs and some other components for good measure. Maybe this board was in a scrap pile and handled roughly.
With the help of the schematics on lisa.sunder.net, we've made some progress, but the person is having a hard time replacing RP3. They know they can just make their own resistor network, but they'd like to add the real part to their parts order if they can. My attempts to find a replacement at the usual sites have come up short, turning up SIP resistor nets that don't really match. Does anyone know better than me how to find a replacement part for sale online?
For reference, you can find a description of the values in the network at https://lisaem.sunder.net/LisaSchem/Lisa210SysIO5.gif, above and left of the CONTRAST LATCH label.
This person also needs to find an IWM for the board --- does anyone have any specific ideas of how they might track down one of those?
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Best bet for the IWM is a dead SE or Plus; SE's can battery-bomb, so it might be easier (and cheaper) to find one of those than a dead Plus. As for RP3, I've also tried locating that to no avail. I'd just planned on doing the same thing and making a network from scratch.
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I'm in the process of assembling the prototype of my I/O board replica right now and I had no luck finding that resistor network either. Places like Digikey and Mouser have very few R2R ladders in the first place and none of the ones that they have match the specs or form factor of the original. The only options that I've been able to find are either stealing RP3 from another I/O board or making the network yourself using discrete resistors. I opted for the second of these two options since I don't want to cannibalize one of my other boards to get my new replica working, but it definitely won't look like the original!
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Another idea, since it's just a SIP, consider making a small board with SIP pins on it that accepts an equivalent SMD resistor pack, or whatever the current thing is that has the same rating.
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I looked a the part on my I/O board, it is a hybrid with no indication of who made it (maybe Centralab)
it would probably be easiest just to take some 1/8w resistors and make a ladder by bending a
lead for the ground and soldering one end of the resistors to it
/--+--+--+--+--+--+--+
| R R R R R R R
| | | | | | | |
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Thanks all! I've passed on the suggestion (just DIY). We'll see what the restorer decides. I hope they find an IWM!
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Thanks all! I've passed on the suggestion (just DIY). We'll see what the restorer decides. I hope they find an IWM!
Maybe also ask them to register on here as well, so there's no back and forth needed?
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Oh, I've tried, but having now already suggested lisalist2 twice and promised that the second time was the last, I'm now enjoying referring to this website euphemistically as "a place not far from here" and to all of you as "wise and determined persons" and "certain... associates online". The restorer is a vcfed mod and perhaps they want to engage their own local community in the fix first.