TM-255 Mods
 

Adjust LOW power setting
The way to adjust low power is to regulate VR401. This trimmer can be found under the speaker (regulates power between 2 and 30 watts).

Adjust HI power setting
To regulate the power of the HI position is to adjust VR601. You can find this trimmer on the back left side
(remove top and locate the  alu cover).

Please be carefully when you dismount and locate the trimmer.

Adjust TX-Power/SWR ratio
At the same place you can find VR603 and that is the SWR protection control. Be carefull when adjusting this trimmer, because it protects your transceiver against bad SWR, but can be usefull when power drops to much on relative good SWR.

Adjust AGC
To adjust the AGC time constant of the transceiver locate VR402 that can be found on the left side at the center when removing the top.

Note:
Please be carefully with these adjustments! All modifications you make is totaly at your own risk.
 

Dear OM's

This is what I found a service technical report from Kenwood acc. TM255 and TM455 9600bps Date November 8, 1994

SUBJECT: Countermessure against modulation during packet 9600bps operation with some older models.

Phenomenon:
A trouble modulation malfunction during packet 9600bps operation was found in the manufacturing process even trough there in input in the DATA terminal.
Pay heed to this trouble in replacing the analog switch IC13.

Cause:
This trouble is cuased by variation in the analog switch IC13.
Even if the 9600bps SW Tr.(Q20:DTA124EK) has been turned ON, the analog switch IC remains unstable.

Counter messure:
We decided to raise the analog switch IC13 voltage while the 9600bps SW TR. (Q20:DTA124EK) is in action by changing the chip resistor R117 in the TX-RX-unit of TM455A/E and of TM255A/E.....etc.

R117=10K to be replaced with 3K3


So if you have problems with those two say to your dealer to ask for SERVICE TECHNICAL REPORT No. B510-94-081E page 1/2 and page 2/2

73's DE PAT KE6MI

Dear OM's

This is what I found a service technical report from Kenwood acc. TM255 and TM455 9600bps Date November 8, 1994

SUBJECT: Countermessure against modulation during packet 9600bps operation with some older models.

Phenomenon:
A trouble modulation malfunction during packet 9600bps operation was found in the manufacturing process even trough there in input in the DATA terminal.
Pay heed to this trouble in replacing the analog switch IC13.

Cause:
This trouble is cuased by variation in the analog switch IC13.
Even if the 9600bps SW Tr.(Q20:DTA124EK) has been turned ON, the analog switch IC remains unstable.

Counter messure:
We decided to raise the analog switch IC13 voltage while the 9600bps SW TR. (Q20:DTA124EK) is in action by changing the chip resistor R117 in the TX-RX-unit of TM455A/E and of TM255A/E.....etc.

R117=10K to be replaced with 3K3


So if you have problems with those two say to your dealer to ask for SERVICE TECHNICAL REPORT No. B510-94-081E page 1/2 and page 2/2

73's DE PAT KE6MIQ

To enter service menu :
Hold down NB and MHz keys + Power ON.

Turn the Frequency Tuning knob to change menu number.
UP/DOWN keys to change value

 A0 Checksum diplay
 A1 RIT center
 A2 IF-Shift center
 A3 LSB carrier point
 A4 USB carrier point
 A5 S-meter adjust S1 (not FM)
 A6 S-meter adjust S9 (not FM)
 A7 S-meter adjust full (not FM)
 A8 S-meter FM start
 A9 S-meter FM full scale
 AA RF-meter adjust low
 AB RF-meter adjust middle
 AC RF-meter adjust high
 AD DTSS single tone frequency
 AE ALC start (microphone gain control by ALC)
 AF ALC zone max (microphone gain control by ALC)
 B0 ALC zone +6dB (microphone gain control by ALC)
 B1 Microphone gain level FM
 B2 Microphone gain Level SSB
 B3 Write to Eprom by pressing UP or DOWN key.
 

• Remove the plastic cover,
• Remove the rubber waterproof seal, and remove the 8 screws on the aluminum cover.
• Set the radio so that the front is facing you.
• Locate VR1 (measure approx. 5cm from the right and 5 cm from the back)
• Rotate VR1 counter-clockwise to reduce the ouput power towards the setting you desire
  Note: the relation between the low- and high power setting is about 2,5 x.
  Example: If your maximum power is set to 50 watts your low power setting will be around 20 watts

ATTENTION
The KB2LJJ takes no responsibility for any damage during the modification or for any wrong information made on this modification.