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                             K E N W O O D
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                        Kenwood Service Centers

   Kenwood Service Corporation             Kenwood Service Center, East
   2201 East Dominguez Street              829 Lynnhaven Parkway, Suite 130
   Long Beach, California 90801            Virginia Beach, Virginia 23452
   Telephone 1-310-639-5300                Telephone 1-804-340-1702

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BULLETIN # 861
MODEL: TR-7800/TR-7850
SUBJECT: TR-7850 Memory Improvements

(Supercedes bulletins 829, 836, 841)

TR-7800 & TR-7850 memory retention may be improved by the following changes 
on the Control and RX units.

Control unit X53-1180-xx

1.If not already present, add a 470k 1/2w resistor (RD14BB2B474J) (R54) on 
the foil side of the board from connector 11 UP line to ground. 
(Units before serial number 1110301)

2.If not already present, add a 470k 1/4W resistor (RD14BB2B474J)
(R55) on the foil side of the board from connector 11 DOWN line to 
ground. (Units after serial number 1110101)

3. Hard-wire the two via holes (through holes without component leads 
installed) along the foil trace between Q18 pin 1 and L1.

4. Change D1 from an XZ-060 (6V, 5%) to a WZ-040 (V11-4102-50) (4V, 10%) Zener.

5. Check D3 for leakage, which would load the MB line voltage below its
normal 5.2V DC settinq.

RX unit X55-1270-xx

1. TR-7800; Change R94 from 56 OHM 1/2W to 150 OHM 1/2W (RD14CB2E151J)

2. TR-7850; Change R94 from 100 OHMS 1/2 to 150 OHMS 1/2W (RD14CB2E151J). 
This will reduce battery charge current to approximately 10 to 12 mA.

3. Cut the foil at the input to Q27, and connect Q27 input to the BB 
terminal Connector 1 for constant battery charge at Power switch Off, 
and floating battery charge when using a TK-1 or BC-1 charger unit for 
memory back-up in base station operation.

4. Check D18 for leakage, loading the MB line.

Notes: 1. With 13.8V DC applied to the radio, and the power switch OFF, 
          adjust VR2 on the RX unit for 5.2V DC at cothector 1, MB terminal.

       2. We recommend using either Sanyo or GE NiCad Batteries. 
          We suggest not using Radio Shack or Eveready batteries in 
          these radios.

       3. If memory loss persists after all changes and checks, suspect 
          control unit Q18 is defective.