SERVICE AND REPAIR NOTES
Bulletin
TECHNICAL INFORMATION / 8000 W. SUNRISE BLVD. / FT. LAUDERDALE, FL 33322

SRN- 1303B
APC 672, 749
Date: June 2000

Memo To: SRN Mailing List 
Deadline: March 31, 2002
From: Radio Product Group / CGISS

Subject: HT750/HT1250 Turns On in Charger (with ON/OFF switch in OFF position)

The user may experience the following when charging a Nickel Cadmium Battery while attached to a
HT750/HT1250 radio (UHF/VHF) in its associated Motorola charger.
Once the battery has reached full charge, (charger green light remains constant) and the radio with battery are left in the charger, the radio may momentarily turn on every few minutes. The radio may emit a beep or beeps and turn back off.

Models Affected: AAH25KDC9AA2AN, AAH25KDC9AA3AN, AAH25KDG9AA4AN, AAH25KDF9AA5AN, AAH25KDH9AA6AN

Serial Numbers: 672TYSxxxx through 672TBPxxxx
                                749TYSxxxx through 749TBPxxxx

The Nickel Cadmium battery has a relatively high internal impedance when it is fully charged.   
The HT750/HT1250 charger supplies a current pulse (1.2 Amps peak) lasting 5 seconds every 5 minutes, once the charger is in the maintenance mode. This is similar to the trickle charge mode in older chargers.
The current pulse applied to this high impedance battery produces a voltage peak that can reach 12Volts during the time the charger�s current pulse is present.
The radio�s electronic on/off switch will turn on, due to conduction of a 10V zener in the path of the electronic on/off switch transistor. The conduction occurs when the supply voltage reaches 11.4V.

Replace diode VR450 with part number 4802245J77 that is located near the flex connectors and can be replaced without removing any shields or the radio chassis. Please refer to the Professional Series Radio Detailed Service Manual for exact component location, part number 6881088C46.

Parts and $35 labor is authorized by warranty. Contact your local Motorola Authorized Service Representative to arrange for this modification. Factory Mutual Approved product should follow the guidelines for repairs and service.