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Old 16 February 2020, 22:18   #1
Marchie
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A2000 keyboard repair.

I have a 'space invader' A2000 keyboard and the number row has stopped working (keypad numbers still good) as well as the up cursor and right shift. I've reflowed, then replaced replaced the controller IC and nothing has changed.


Kind of stumped, any ideas for troubleshooting this?


(This keyboard is too good to let die!)
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Old 16 February 2020, 23:09   #2
aeberbach
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My guess (without looking at the circuit of A2000 KB specifically) is that you have one column not working correctly - there is possibly one line in common across the numbers and the up and right shift keys. Or else, two traces close together may have been damaged if all those are not on the one circuit. It sounds awfully like the pattern of connections I found when making my A1200 replacements.

Looks like you have some ability to debug too but if you feel someone else might have more luck I could look at it for you. I'm in Melbourne.
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Old 18 February 2020, 11:59   #3
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Yeah, I guess I thought the circuits always went in weird diagonal patterns, so having a straight row out seemed odd (but I'm far from an expert).

Have you any experience taking these apart? I've dissassambled a few A500/A1200 keyboards, but not one of these - the pcb/membrane doesn't seem to want to come away from the plastic chasis holding the keys even after the screws have all been undone (and I don't want to risk breaking it by force).

Thanks for the repair offer too - I have some go-to people in Sydney, but it always helps to have backup options.
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Old 18 February 2020, 22:52   #4
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Probably best to wait for someone to comment who has done it recently - I think I did it in 1994 or so

Any chance it has had anything sticky spilled on it and it is just a bit stuck? Tried warming it gently with a hair dryer?
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Old 18 February 2020, 23:25   #5
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There is every change it's just a bit stuck - hair dryer might be a good idea.
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Old 27 February 2020, 23:55   #6
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Ok, so the switches are actually soldered straight onto the pcb (with that black plastic bit inbetween), so I'm not getting them off anytime soon. The upside is that means it should be a single-sided PCB no?

According to this link the keys I've lost are all on the same row ("row1, bit 3" whatever that means). Whilst I can't see any faults in the pcb, but there HAS to be a broken connection somewhere on that track right?

Could it be a bad connection coming out of the IC?

Anyone have a schematic for the various models of A2000 keyboard?
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Old 28 February 2020, 01:19   #7
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Yes - almost certainly a scratch across a thin trace or similar. If you can't find the actual break you could just find the last point where you know the signal is good and use some 30AWG wire to connect it to the right input pin of the decoder.

This is almost certainly a two-layer PCB so if one side of the PCB is covered with something and you can't see it, maybe the break is under there. And maybe if it's covered it got corroded due to a liquid spill of some kind. Always hard to tell without looking.
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