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TUCoPS :: Radio :: ic751_4.txt

Icom IC-751 Mods


Subject: IC-751 Bad Cap Problems

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This info may be helpful to ICOM-751 owners with units approaching five
years of many operating hours; two UNRELATED problems occurred, both due
to a similar 10uf electrolytic opening up.  The first was the input cap.
to the 5-volt regulater chip which supplies PLL board. Proper by-passing
is required, probably to prevent internal oscillations in the chip. 

Replaced it with a tantulum. (Also arbitrarily replaced electrolytic on
the output side of the 5-volt reg. chip). The symptoms were 3 or 4 minutes
delay before unit would function.   Also the screw holding the reg-chip to
its heat-sink was a little loose...probably due to COLD-FLOW characteristics
of aluminum.  This can also occur in pheof aluminum.  This can also occur in phenolic P-C boards where the ground-
foil is supposed to be bolted tightly to the chassis. It would probably be a
good idea to use small split-ring lock-washers (along with flat-washers) in
these cases to maintain tension over time.

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