Hi - I recently picked up a descent IIc and it booted fine but the keys didn't work. I checked to ensure the keyboard button was engaged and disengaged but still no keys work. However, control and reset does reboot the machine.
I have tore the machine apart to clean up the components and inspect them. I also took all the keys off and cleaned up the key connectors and also checked for continuity. All seems fine.
After reassembly I have the same issue. The keys simply won't work except the control and reset.
Does this seem like a bad keyboard chip on the logic board?
Thank you in advance.
Could be.
Grab the schematic (https://archive.org/details/Schematic_Diagram_of_the_Apple_IIc/page/n1/mode/2up) and check the encoder IC for +5 and -12V. Also look at the KSTRB signal at the IOU. Should be easy to track down the issue.
Thanks I'm going to be back to testing it tonight. I did plug another confirmed working keyboard in and had the same result so I know it's something going on with the logic board/chips.
I'll check out the schematic and start testing.
Curious - I don't have an oscilloscope but have a multimeter. If I set my multimeter to 20v DC can I still test for the +5 and -12v readings?
I swapped the IOU and still had the same results.
I want to verify the encoder IC and also recheck all the PCB traces.
Sure. You might be able to see the strobe pulse as well if you look close.
20VDC means that it uses a 20V DC baseline: It will 'max out' at 20VCD on that setting. You can check 0.2VCD on that setting, or 5VDC, or 12VDC. It doesn't matter. Negative and positive polarity from - 20VCD to + 20 VDC is the range for that.
Most units max out much higher than that, and have settings at least to 400VDC for very limited and cheap models. Likewise, most units have lower thresholds of 2V, 0.2V, and so on.
Hi! did you ever find a fix for this problem? I have the exact same thing happen to me suddenly and I cant find a solution anywhere.
Check the keyboard cable, reseat all chips that are in a socket. (I saw a similar post on FB Apple II group today, and if you are the same person, then you've already done this)
If that does not work, then with my limited knowledge, I am guessing it could be the keyboard encoder chip, labelled KR3600-PRO. Unfortunately on IIc, both A2S4000 (without memory expansion header) and A2S4100 (with memory expansion header) models, I believe this chip is soldered onto the board directly without a socket, which makes it a bit harder to test and replace.
I say this because when the KR3600-PRO chip died on my IIe a while ago, only the reset-ctrl, reset-ctrl-(open/close) apple key worked. Like you (according to the FB post description), none of other keys worked, but instead of nothing being printed on the screen, in my case, random keys were printed continuously on the screen, even though I was not pressing any keys. I replaced the keyboard encoder chip and everything was back to normal. Luckily on IIe (PAL version anyway), the chip was in a socket so it was easy to replace it.