[Icom] IC 751 problem

[Morrison Hoyle]

I wonder if anyone has any pointers to the solution of this problem.

I know this is an old radio but it has done so well in the 15 years approx
that I have had it so I am reluctant to abandon it.

On switch-on, the radio occasionally works perfectly, but most often, the PLL
system seems to fail to work.  All the indications are OK, no movement on the
S-meter and no signal received.  The way I get it to work is to switch to
memory mode and start the scan of the 32 memories.  Sometimes the radio will
spring to life in a minute or two, but sometimes it can take 15 to 20
 minutes.

Another associated problem which fortunately doesn't happen too often is that
after working OK for an hour, shifting the VFO does NOT change frequency.
The displayed frequency changes but the received frequency doesn't change
until I have moved  by quite a lot - say 50 Khz.  Then it moves to some
random frequency which I cannot control.

Obviously the PLL board is more than a bit sick.  I have changed the 4
plastic trim caps for ceramic as advised by Icom and some of the
electrolytics on the board have also been changed.  The 7805 regulator which
got extremely hot has also been replaced and the upstream 10 ohm resistor
replaced by 15 ohms to reduce the heat dissipation of the 7805.

I suspect a dry joint or cracked track on the PCB.

Has anyone got any ideas?  Has anyone got a 751 which doesn't seem to work
but the PLL board is believed to be OK which they might part with?

73 - Morrison
VK3BCY qthr

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