Service BulletinAmateur Radio Division

Subject: TS-660 - Microprocessor LatchupDate: January 25, 1982

Microprocessor latchup may occur if the power switch is cycled several times in quick succession, if the supply is turned off while the power switch remains on, or if the power supply is turned on with the transceiver already on. Symptom will be no display, erroneous display, or locked display. Change two components on the control unit to prevent further trouble.

On the control unit X53-1220-00:
  1. Replace R23 680 ohm with a 470 ohm resistor (RD14CB2E471J).
  2. Remove and delete C4 47uF
  3. Add a 22uF 16V electrolytic (CE04W1C220M) on the foil side on the board between D24, R23 (positive) and ground (negative).

NOTE: Changed capacitor is marked RED.

  1. This change applies to units before serial number 209xxxx.
  2. Installation time for this procedure is 1/2 hour or less.

©1981 Kenwood