Memotech Limited MTX 500, Service Manual

Page: 44 / 78

40
SYMPTOM 9
Add on faults - e.g. Memory expansions, Rom boards,
RS232, Printers etc.
a)
Cause of Trouble
Memory upgrade not obtaining Ram top
Check Point
Check for correct prom coding, see page 45, check
rams in sockets (if any) for poor connection
Repair Method
1 If prom is o.k. make sure that both edge
connector and upgrade connector is clean.
2 Check links on the upgrade are correctly
soldered in the LO position.
3 R1 = 330 OHM.
4 R2 = 680 OHM.
5 If green screen fault refer to Rig Ram Test.
b)
Cause of Trouble
Rom Boards
Check Point
RE/CPM pin 9, 5A, 74LS273N of MTX
Repair Method
1 Type Rom 2 whilst probing pin 9 of main PCB -
location SA. Look for pulse
2 If pulse is absent, check foe washer on
underside of board - under TIP 2955
3 Check pal chip on MTX.
MTX Service Manual