Modifications for the Yaesu FT-102
Yaesu FT-102 mods
LOW RX SENSITIVITY : Check aerial i/p fuse which is a small wire
ended bulb located on the small pcb in the top PA compartment.
It is not possible to use any old bulb here as most will give
several dBs attenuation.
INTERMITTENT LOW RX SENSITIVITY : Suspect the relays on the RF
pcb around the RF amp. Note that some of the relays are 24v
types and not the more usual 12v. Don't miss the relay at the
front of the board under the shaft of the bandchange switch
which is difficult to change. I have often tried to clean the
relays but they usually go intermittent again within a few weeks
- it's better to change them.
RF AMP NOT WORKING : Check the relays which switch the RF amp
and then check the two fets in the RF amplifier (2SK125).
PRESELECTOR NOT TUNING CORRECTLY : There is a shaft coupler on
the bandswitch shaft - if the screws in this are loose it is
possible for the front and rear sections of this switch to be
out of physical alignment.
NO RF OUTPUT (PA DRAWING CURRENT AS NORMAL) : The main aerial
changeover relay (on pcb in the top PA compartment) has been
known to burn out.
VARIOUS PA FAULT CONDITIONS : Check for physical short circuits
around the band switch in the PA compartment. I have once had
burnt out tags on the bandchange switch - this was impossible to
see before I removed the switch.
FLUCTUATING POWER OUTPUT : check the PA valves and check the PA
INTERMITTENT MAINS FUSE BLOWING : Suspect that one of the PA
valves is flashing over occassionly.
NO TX : Check the series pass transistor in the 12v. regulator
circuit. I have twice seen cases where it has overheated,
melting the solder on its leads, causing a physical short
NO TX - NO DRIVE : R01 on RECT A UNIT. Check driver valve after
POOR NEUTRALISATION : This can sometimes be a problem if 2 or 3
different types of valves are used in the PA.
PA WON'T NEUTRALISE : I had one case where the user had
connected the PA screen grid supply to a higher voltage on the
rectifier unit, causing this problem.
FREQUENCY SHIFTS WHEN CLARIFIER ON : Dirty contact on RL4001,
the clarifier relay.
FM TX WAY OFF FREQUENCY : Failure of Q13 (TC5081P) on AM/FM
unit. See Yaesu mod sheet to prevent further failure.
LUMPY VFO DRIVE : The couple of occassions that this has been a
problem I have usually improved it by cleaning and relubricating
the mechanism. If its really bad the drive will probably need to
KEY CLICKS : Some of the earlier models suffered from key clicks
on CW. To cure this connect a 0.68 microfarad cap between key 1
on the REC A board and earth.
DRIFT ON CW : Some of the early units suffered from a drift of
50-100Hz during the first couple of minutes of CW transmission.
Yaesu suggest removing C153 (3.3 microfarad) on the local unit
to cure this problem. It is located between X4002 and T4014.
NO 29-30 MHZ : See CB de-modification below.
CB DE-MODIFICATION : See Yaesu mod sheet. The CB modification
allowed the 29-30Mhz range to cover 27-28Mhz and the counter did
not display CB frequencies. Careful alignment of the VCOs is
This counter shows the number of hits since the
9th February 2000
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