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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Loki762 on August 09, 2024, 12:21:46 PM
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I have bought an Amiga 500, and it seems that sometimes the keyboard works while other times it does not. The keyboard has a green PWR LED.
I have also borrowed two other A500, and one of the keyboards are working all the time - this keyboard has a red PWR LED, while the other one (also having a green LED) does not work - but I do not know if the keyboards actually work or not, though the one at least seems to work.
Are there any good advice to what I could look into, to get my keyboard working?
The image is with my periodically (mostly not) working keyboard.
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I have now tried getting another set of CIA chips from another A500, but with same result - so the problem is not the CIA chips (I also gave the sockets a good amount of contact cleaner).
I have also tried resoldering the cable-joint on the keyboard and cleaned the ribbon cable - but still same result.
Discovery 1:
I have noticed that when the keyboard seems dead in Amiga Test Kit, then I can do a soft reset from the keyboard - so at least there is SOME kind of connectivity - but none of the soft reset keys seems to be working (no display in UI), when typing in the keyboard test of Amiga Test Kit.
Discovery 2:
When it works (after a few minutes of power-off), then I can do a soft reset and then it will work again after that, when typing in Amiga Test Kit. I can do this (soft reset) continuously and it will continue to work - but then as soon as I do the power-recycle, then the keyboard dies in Amiga Test Kit.
Is this a capacitor issue on the keyboard? Shall I replace all of these?
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My keyboard is a Mitsumi and I assume the model is A620A.
I am not sure here, if this is the exact same model or if there are many different revisions, but I did find this list of components for the keyboard, https://eab.abime.net/showthread.php?t=81893 (https://eab.abime.net/showthread.php?t=81893)
C3 = 22uF 16V
I do have a 22uF 25V - would this be okay?
C5 = 10uF 16V
I do have a 10uF 25V - would this be okay?
C10 = 1uF 16V
As far as I can see on my keyboard, it does have a 1uF 50V installed, so I assume I am okay to replace this with another 1uF 50V?
Do you see a need for any of the other capacitors, as I do not have these in stock?
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After a long looong time of troubleshooting and pulling my hair, then I did figure out the issue for this one - it was missing GROUND.
I did dismantle my keyboard, and did have the print "hanging loose" - not screwed in place, as I was doing test. I did have this setup for the most of the time, until I gave up for now and screwed everything in place again, to not loose the screws - and then it suddenly did work!?!!
After some retesting, I could confirm this - when the keyboard print is not connected to the ground plane of the keyboard, then you will experience this problem - or rather, at least I did - not sure if this is typical or not.
Quite a weird problem for me, but luckily it is now solved and partly understood 😂
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Hmm.. I was sadly too quick in my conclusion, as it has reverted back to "normal" bad behavior now.
The CAPS LOCK does blink with the one-blink sequence, so maybe this is the large IC on the keyboard print - is this the keyboard ROM?
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The Chip is the keyboard MCU - basicly a separate little computer on its own.