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FT736R Power Supply



Thanks to everybody who replied with help, suggestions or just words of
encouragement.

Here is the summary of what was suggested and implemented:

A bit of Background:
My FT736R is about 5 years old, and I have over the years added the
optinal Frequency modulles to it (50MHz and 1G2). These modules fit
right next to the Power Supply and restrict the Airflow arround the
power supply (also they consume power...)
The net result of this is that the FT736 runs warmer than without these
additional Modules.

Examining the Power Supply confirmed the smell that I had been smelling,
the PCB under R17 and R18 had been very hot, showed brown/black
decoloration.

The suggestions:

Examine the electrolytic capacitors in that area: C9 (220 uF/16V) and C?
(1 uF/50V). Repalace at least C9, likely to be dried out. Be sure to
replace the capacitors with 105 degree C types.

Examine the solder Joints of R17 and R18. Resolder these and better:
place these Resistors Vertically so that the air can better circulate
arround them.

Place a small Fan in the Power Supply cooling the suspected area. 
Fans used to cool 486 processors have a size that fits nicely in the
PowerSupply, fed throug a small resistor to reduce the acoustic noise
level they provide a welcome additional circulation in the crammed space
inside the FT736. The fan takes it's powe directly from the Power Supply
output (13.6V) and will continue to turn a couple of seconds after
powering off the radio whilst the power supply discharges.

All these suggestions heve been implemented now in my radio, the
temperature of the radio is moderate (hand warm), the acoustic noise
level is quieter than my already quiet PC. The Radio has been on
continuously for the last 4 days, it looks like the combination of all
these cures did the trick

Thanks again for all the replies

Arne
KF6EDK / PA0KKV

p.s.
Of course it is possible to feed the radio from a separate Power Supply,
even Battery Backup is possible that way, it was not a road I wanted to
take however. Thanks for the suggestions though!
A.

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