Modifications for the Yaesu FT-102


19-07-1998 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 anode choke.

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 circuit.

NO TX - NO DRIVE : R01 on RECT A UNIT. Check driver valve after replacing this.

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 be replaced.

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 essential.