FRG7700 - FRV7700

 

FRG7700 - FRV7700

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** NOTE THAT MOST OF THE PROBLEMS WITH INTERMITTENT INCORRECT

FREQUENCY DISPLAY ARE CAUSED BY THE PLL GOING OUT OF LOCK. IF

THE FAULT IS AN OCCASSIONAL INTERMITTENT ONE, IT IS WORTH JUST

FULLY REALIGNING THE PLL, THEN GIVING A LONG SOAK TEST.

NO AUDIO OUTPUT : Check the audio ic.

DISPLAY READS APPROXIMATELY 39MHZ : This fault may well be

intermittent. Early versions of the 7700 sometimes suffered from

this fault due to low outout from the PSU bridge rectifier when

it had got hot - replace the bridge rec. The fault can be caused

by some PLL faults, and also by lack of local osc signal fed to

counter circuitry. Check alignment of PLL. Q25 (MC 4044P) has

given problems on a couple of occassions. Check for bad

connections on the interconnecting cables between the PLL and

the control circuitry.

DISTORTED SSB RX : The bridge rec in the p/s can cause this

problem. If it goes faulty the power supply volts drop as the

unit warms up. This drop in voltage can cause problems with the

PLL not locking.

DRIFTING : Bridge rec as above.

HUM ON RX : Bridge rec as above.

VFO DOES NOT TUNE OVER THE FULL 1MHZ RANGE : If the tuning

appears to stop before the VFO has reached the end of its tuning

range on all bands then check the alignment of T2007.

UNIT DOES NOT TUNE ON SOME BANDS : Check alignment of the four

main VCOs in the PLL. Also check for dry joints or cracks in the

print around the band change switch.

FAILURE OF ONE OF THE RECEIVE MODES : Check the mode switch,

which has given problems on a few occassions.

MEMORY FAULTS : On the few occasions when I have had memory

faults, it has always been traced to on of the random access

memory chips.

BAND CHANGE SWITCH SELECTS WRONG BANDS : If the RX works ok

otherwise, then it is worth checking that none of the memory ics

are outputting data when the MR button is not depressed. (This

assumes that the band change knob has not come loose and slipped

out of position).

INCORRECT SEGMENT ILLUMINATION ON DISPLAY : Check the SIL

resistor networks around the micoprocessor outputs. Check the

microprocessor.

NO AUDIO : Check the audio o/p ic.

FRV7700

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NOT RECEIVING : Check the output emitter follower transistor Q03

- this is a very common fault.

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