Memotech Limited MTX 500, Руководство по обслуживанию

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32
b)
Cause of Trouble
Faulty Bridge Rectifier
Check Point
Check your +5v and +12v
Repair Method
1 If signal is poor trace fault from either the
7805 or 7812 Regulators to faulty component.
SYMPTOM 5
When power is switched on:- Green screen and humming
noise.
Whilst testing the MTX during Manufacture the most
common fault we find is:- On fire up - Blank screen
and humming sound. Quite frankly these are the most
difficult faults to repair due to the fact that just
about any component can cause these symptoms. We find
that solder shorts are responsible for the majority of
these problems, but occasionally we do find faulty
components.
Since all the MTX's are thoroughly tested before
despatch, faults occurring such as green screen and
humming, after despatch are more than likely going to
be component break down.
The biggest problem is whether or not the ram chips are
functioning correctly or not. The Memotech Ram Test
Rig can pin point a fault either on the data bus or the
memory page address lines. Whether or not the Rig
detects a faulty Ram the fact remains that it will
eliminate eight key components which is a great help.
Without a Ram Rig Test the chances of finding a faulty
Ram with only an oscilloscope are very slim indeed.
However, green screen and humming faults are not
necessarily due to faulty Rams. When you have the
symptom of green screen and humming there is a strict
procedure to follow.......
MTX Service Manual