Memotech Limited MTX 500, Service Manual

Page: 37 / 78

33
a)
Cause of Trouble
Faulty voltages
Check Point
Check all your voltages 0v, 5v, 12v, -5v, -12v
Repair Method
1 If any signal is absent follow offending
circuitry from source and repair.
b)
Cause of Trouble
Faulty RESET circuit - also see page 29.
Check Point
Check Points are:- Pin 3 of IC18 BCN4070 CMOS
Pin 26 of C.P.U.
Pin 34 of V.D.P.
1 If signal is low - trace fault back from Pin 3
of IC18 4070CMOS (pay particular attention to
C11 10uf cap).
2 If signal is high RESET circuitry is o.k.
NB. Signal should go low when shorting pins 19 and 20
of J1 - keyboard interconnection header plug.
c)
Cause of Trouble
Fault on address bus
Check Point
Probe system address bus of C.P.U.
MTX Service Manual