Memotech Limited MTX 500, Service Manual

Page: 41 / 78

37
d)
Cause of Trouble
MTX 512 with internal expansions only
Check Point
Check right hand bus connector
Repair Method
1 Either make sure the bus connector is clean
or...ideally hard solder the expansion board to
the mother board.
NB: Before these tests are carried out always check
that you have a good tape recorder that is set
at the correct volume (between level 7 and 10).
Check your cassette leads (remember ear to ear
and mic to mic). Check that the cassette tape
itself is working - and not damaged.
SYMPTOM 7
Problems with sound (Depress control key and G key
together for note).
a)
Cause of Trouble
Faulty SN 76489 AN (5E)
Check Point
Start by probing I/O of (4E) 74LS374N
Repair Method
1 Press control G - you should be getting pulses
from 4E 74LS374N outputs. If absent disable
offending output from 5E SN76489.
2 If still absent 74LS374N is faulty.
3 If pulse is present on 74LS374N the 76489 is
faulty.
MTX Service Manual