MTX keyboard fast troubleshooting
Posted: 02 Jan 2014 21:00
A passive key matrix it’s attached to J1 connector of MTX motherboard.
Implementation on reading keyboard it’s performed by IN,OUT Z80 instructions.
Surfing on the internet it’s hard to find keyboard layout, so I performed my own investigation
.
Results are shown in the following picture:
There is a discrete logic involved in the process, IC related are 2A, 3A and 2E, also IC provide the Enable signals for both IN5 and OUT signals, these are 7C and 7D
here is the isolated section:
Some things to take into account:
- If a single key doesn’t read, maybe a mechanic problem.
- Also consider some cut in cable that joins keyboard with motherboard.
- Over connector J1 you can test individual keystrokes, closing pins according keyborad matrix above attached.
- More unusual, but possible, the keyboard board itself, can have any cut o cold soldering.
- Always test the resistance set R0 to R7 and diode set D0 to D7
- If an entire row, alternates key doesn’t read, probably IC 2A and 3A are involved.
- In any case always consider 2E that acts a level buffer to help decode keys pressed and stored by 3A.
My case
My MTX, lacks in keys P I Y R and W. The rest of keys worked well, even shifted
.
After testing mechanic parts, cable the error was located on IC 2E, this is the explanation: one flip-flop acting as buffer on line D2 was out of order
Implementation on reading keyboard it’s performed by IN,OUT Z80 instructions.
Surfing on the internet it’s hard to find keyboard layout, so I performed my own investigation
.Results are shown in the following picture:
- MTX_keyboradweb.jpg (67.98 KiB) Viewed 9439 times
here is the isolated section:
- keyb_schem.jpg (90.83 KiB) Viewed 9439 times
- If a single key doesn’t read, maybe a mechanic problem.
- Also consider some cut in cable that joins keyboard with motherboard.
- Over connector J1 you can test individual keystrokes, closing pins according keyborad matrix above attached.
- More unusual, but possible, the keyboard board itself, can have any cut o cold soldering.
- Always test the resistance set R0 to R7 and diode set D0 to D7
- If an entire row, alternates key doesn’t read, probably IC 2A and 3A are involved.
- In any case always consider 2E that acts a level buffer to help decode keys pressed and stored by 3A.
My case
My MTX, lacks in keys P I Y R and W. The rest of keys worked well, even shifted
.After testing mechanic parts, cable the error was located on IC 2E, this is the explanation: one flip-flop acting as buffer on line D2 was out of order
- image.jpg (157.74 KiB) Viewed 9439 times