Memotech Limited MTX 500, Service Manual

Page: 43 / 78

39
Repair Method
Generally key bounce is caused by faulty key board
switches. Simply de-solder and replace the
offending key(s).
b)
Cause of Trouble
Key(s) u/s
Check Point
J1-keyboard interconnection header plug
Repair Method
1 Check that the keyboard interconnection cable
is secure and not torn.
2 Check that the offending keys work by buzzing
across the terminals whilst depressing the
switch.
3 Check for pulses on diodes DR0-DR7 (4148) Anode
-> 74LS273N (3A) -> LCD lines.
c)
Cause of Trouble
Incorrect character displays
Repair Method
1 Check for correct language switch setting at
PCB location - SWA.
2 Ensure GROM line is connected (piggyback Roms
only).
3 Check links 1, 2, 4, 5 and 13 (4000/04 boards
only).
4 Replace PAL14L4 chip.
MTX Service Manual