Modifications for the Kenwood TM-455

19-07-1998 Solution 9k6 TM255/455 English language
23-04-2000 TM-455A/E Change in pin diode English language

Solution 9k6 TM255/455

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.

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.

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


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TM-455A/E Change in pin diode
Author: Kenwood Communication, inc.

Service Bulletin no. 1058 (6 May 1994)

Some early versions of the TM-566A/E have been discovered with a bad solder connection at the final module pin diode, D601. If the impedance of this devices is too low, the power consumption for this devices goes up. This increased power consumption might cause excessive heating of the solder connections, and may result in a failure of the connection(s) after long FM transmission.

On the TX/RX unit replace diode D601 with a UM9401, change R606 to 100 ohm, change C623 to 5 pF, and C624 to 12 pF. After replacing these parts, readjust the NULL and Protection circuit using the procedure provided in the service manual.

Parts required:

Qty   Description                          Part No.         Circuit Description
 1    Pin diode                            UM9401           D601
 1    100 ohm chip resistor                RS14DB3A101J     R606
 1    5 pF chip capacitor                  CM73F2H050D      C623
 1    6 pF chip capacitor                  CM73F2H060D      C624

Time required for this modification is 60 minutes or less.

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