deskthority

Just so we can close this case - replacing the 8039-11 MCU on the keyboard fixed it. It also revealed further issue with intermittent key press registration, which was easily fixed with a solder iron - most of the switches had broken solder points due to how the switch backing plate and the PCB boar...

A small update: while we wait for the new MCU, my friend had an idea to run the code we got off the EPROM on an Intel 8048 processor emulator software. It seems to load and run as intended, scanning ports etc.

MMcM wrote: ↑

26 May 2020, 04:15

Got it. Sorry for misreading what you said earlier.

If RESET being asserted all the time has been ruled out, then I guess, yes, wait and see how a new MCU does.

I will report back after the replacement chip arrives from the Big Rock Candy Mountain. Thanks again MMcM!

Perhaps I was not precise enough - the MCU sets the address line at 0 (or it doesn't and it's just "default" value) and then receives value from byte at address 0 in the EPROM. This value is binary 04, and disassembler translated it to part of an initial JMP instruction. Below is first few lines fro...

MCU is not advancing the address lines. It just keeps getting first byte off the EPROM (04, as seen in the dump binary we got off of te EPROM). ALE and PSEN signals from MCU look good, but it just keeps asking for the same byte all over. Ordered a replacement 8039-11 and will post an update when it ...

So we had some time today and together with my friend we hacked together an ATMega8 based EPROM reader on a breadboard. We successfully dumped the contents of the keyboard's EPROM chip. It seemed to be a valid code (definitely not full of FFs or 00s), and disassembled nicely when fed into DASMx. The...

Thank you very much MMcM, this is exactly the kind of advice I was hoping to get :) Time for more playing with the analyzer. It'll be few days before I can do it though, but I shall be back with my findings (or further questions). Forgot to add: yes, the LEDs come on and stay on. Good catch! I'll ch...

TheInverseKey wrote: ↑

22 May 2020, 05:53

I had the same issue as well with mine something is off with the clock for sure.

Thanks! So it's either the built in clock in the micro controller, or the external quartz visible on the board? Did you manage to fix yours in the end?

Hello fellow keyboard maniacs. I've just created this account but I have been a passive reader for a good while. I am struggling with reviving this keyboard I acquired some time ago, which I really like and want to save from oblivion. Before I totally wreck it, I thought I better ask the elders.. Pa...