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Compaq Portable keyboard problem

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First post, by Cabernut

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So I have this Compaq Portable - 8088 with two floppy drives and a ram upgrade board. I found it at a thrift shop years ago for $20. It used to work until the keyboard foamies disintegrated. So I went on ebay and bought replacements(see picture).

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I went through the long process of replacing them, and while doing that I remember that I could type on the bare board with my fingertips. Anyway, upon reassembly I noticed that my repair didn't work at all. In fact, nothing worked. I was getting error 301

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So what happened? I checked the voltage regulator on the keyboard circuit board, and they were 12v on the input and 5v on the output. So that appears fine. There does appear to be a tiny amount of corrosion on some of the bare traces. But that might not explain how it was working before my failed repair.

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What could it be? Anything else I can check? Or, is there a way I can temporarily patch in an AT keyboard connector? I really would like to tinker with(coding and games) this computer more, perhaps find a hard drive for it and run 8088 Domination on it just once.

Reply 1 of 5, by Cabernut

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Well, I dug this one out again to finally track down the problem. I tested the suspect traces above and they're good. I also tested the keyboard cable for any broken wires or bad contact, it was good. 5V regulator was still working fine and output was 5V to the vcc pin on the chips. I finally removed all the boards including the motherboard, re-assembled/re-seated everything. Still the 301 keyboard error. I found the manual entry for the 301 error and and it said to "replace the keyboard". As if it were that simple... I suspect there is a bad chip in the keyboard. It's too bad they used such a proprietary internal keyboard connector(6-pin, 12V power) . Not really fixable by me at this point. I'm not expert enough to find the bad chip and replace it, even though many of these old chips can still be ordered online.

I suppose I'll have to keep an eye out for another keyboard. Might take a while though. That about wraps it up for now. I may be getting my hands on a working Apple ][ soon so that might be fun to tinker with in the mean time....

Reply 3 of 5, by Synoptic

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Hi! Digging this old thread. Same issue here. BUT I managed to patch an XT keyboard and it works. There’s is a way to send 5v instead of 12v to the keyboard by doing a small mod to the motherboard.

Reply 4 of 5, by Cabernut

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Wha-hey! You say you've managed to get an XT keyboard working with yours? What exactly was done and could it be done without modifying the motherboard? Perhaps with and in-between voltage regulator or something of the sort?

I don't know what the pinout of the built-in square keyboard connector is, but I suppose given the right pinout, drop the volts down to 5, I guess that's all that's needed essentially?

Reply 5 of 5, by Synoptic

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Cabernut wrote on 2022-09-20, 03:25:

Wha-hey! You say you've managed to get an XT keyboard working with yours? What exactly was done and could it be done without modifying the motherboard? Perhaps with and in-between voltage regulator or something of the sort?

I don't know what the pinout of the built-in square keyboard connector is, but I suppose given the right pinout, drop the volts down to 5, I guess that's all that's needed essentially?

I modified the motherboard. Everything is already there to put a 3 pin header to use a jumper. Only need to cut a trace on the underside.

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