Memotech Limited MTX 500, Service Manual

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34
Repair Method
1 If any address signal is absent - Reset MTX
whilst probing. If signal is still absent -
start by replacing C.P.U.
2 Check both 74LS157's (PCB Location 6C and 6D)
to see if they are multiplexing.
3 If 74LS157 pin 1 pulse is absent, check pin 14
of PAL14L4 and follow circuitry through pins
3,4,5 and 6 of the 74LS04 (PCB Location 2B) to
REF points MPX. faulty.
d)
Cause of Trouble
Faulty system data bus
Check Point
Probe pin 2 or 14 of all rams
Repair Method
1 If signal is absent reset MTX whilst probing.
If signal is still absent refer to MTX Rig Ram
Test.
MTX Service Manual