Modifications for the Kenwood TR-7625

19-07-1998 Alternator Whine, TR-7600/7625
Author: Trio-Kenwood Communication, inc.

Service bulletin no. 39 (9-7-1979)

In some mobile installations, alternator whine may be heard during transmit. External B+ filtering does not have sufficient effect.

In some instances, using the cigarette lighter will cause this problem. Running off the fuse block, and even directly from the battery may still not eliminate the noise.

First, check power line routing in the engine compartment. It should be kept clear of all secondary HV harness wiring, and clear of the alternator, regulator, and ignition primary circuits. Careful routing should reduce or eliminate noise coming in through the power line.

Check for clean ground connections at the antenna and radio.
Check for clean and tight battery connections.

If all of these measures fail, replace L22 on the VCO unit X50-1580-10 from the original green coil, to either an orange or black coil. No adjustments should be necessary.

Old part number L40-1021-03 1mH
New part number L40-1021-43 1mH

Please notate your Service Manual.

19-07-1998 TR-7625 Intermittent TX
Author: Trio-Kenwood Communication, inc.

Service Bulletin no. 804 (7-2-1980)

When servicing a TR-7625 for mechanically intermittent TX, check the heavy WHITE DRB lead at the push-on connector directly in front of relay RL1 on the RX TX unit.
This post may either become seperated from the land, or the land may crack from vibration. Resolder the post, plus reinforce the connection with a small piece of solid wire soldered on the foil side of the board.

20-02-2000 Correcting Frequency Difference Between RM-76 and TR-7600/TR-7625
Author: Trio-Kenwood Communication, inc.

Service bulletin no. 33 (19-3-1979)

The RM-76 will be about 500Hz higher in frequency then the TR-7600/TR-7625. This will not present any problem most of the time. Out specified tolerance is ±750Hz.
The operating frequency may be out of the receiver input of a repeater if the transceiver is turned slightly high however.
The frequency difference may be corrected by adding additional diodes in series with both the 02 and 52 lines in the RM-76. This is shown in the figure below.

The foil paths from the connector to diodes D18 and D19 are cut and the new diodes soldered on the foil side of the board. The cathode and of the diodes is soldered to the connector side. We recommend using either 1S2076 or 1S1555 diodes.

20-02-2000 TR-7600/7625 Audio tone on TX
Author: Trio-Kenwood Communication, inc.

Service bulletin no. 45 (10-8-1979)

Some TR-7600/7625 users report a 0w-background tone during TX, especially noticeable at full quieting by the receiving station.

On the PLL unit X50-1580-00, changes:

New Part L18 33uH L40-3301-03

20-02-2000 TR-7600/7625 Optional ceramic filter
Author: Trio-Kenwood Communication, inc.

Service Bulletin no. 50 (9-8-1979)

Adjacent channel rejection may be improved by changing one capacitor & installing an optional narrow ceramic filter. On the TX RX unit X44-1320-10, change;

Old Part L41 L72-0309-05 CFT-455 F2
New Part L41 L72-0306-05 CFL-455 F

18-03-2000 TR-7600, TR-7625 Battery Memory Backup
Author: Trio-Kenwood Communication, inc.

Service Bulletin no. 806 (7-2-1980)

Memory in either radio may be retained by installing a battery inside the unit. This feature would be useful when transporting the radio base to mobile, or when operating base. The AC supply can be shut off while retaining the single memory.

Obtain and install a small 6V DC battery, appropriately secured and insulated, inside the radio. Wire as illustrated through a diode. Current drain will be approximately 0.5 mA with the mail supply OFF.

19-03-2000 TR-7625 Final module replacement
Author: Trio-Kenwood Communication, inc.

Service Bulletin no. 820

When replacing the output hybrid with a "red dot" unit, an additional 47pF cap must be installed between the M57712H output terminal and the RFO warp post.

Install the M57712H with white silicone heat sink compound. Install a 47pF as shown between the hybrid output and the RFO terminal. Spread L21 as necessary for at least 30W output at approximately 5.5A total current consumption.

Note: Hybrids not having a red Mitsubishi logo do not require the additional cap or adjustment.

19-03-2000 TR-7625 Hybrid amplifier module substitution
Author: Trio-Kenwood Communication, inc.

Service Bulletin no. 826 (30-5-1980)

(Supercedes #820)

Final modules obtained from Trio-Kenwood Communication’s Parts Department after 1/5-1980 MUST be installed as outlined. Two versions of the hybrid may be supplied, either marked as an M57712H, or as an M57733. This information applies in either case.


  1. Remove and delete C49, 22pF
  2. Add a ground lug adjacent to the RFI terminal.
  3. Add 10pF across the RFI terminal and ground.


  1. Adjust TC2 for maximum output at 146MHz-
  2. Adjust VR4 for 5W output at 146MHZ, low power.

New part: 10pF C45CH1000