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TR-7800, TR-7850 Memory Improvements
TR-7800 & TR-7850 memory retention may be improved by the following changes on the control and RX units.
Procedure
Control unit X53-1180-xx
If not already present, add a 470 Kohm ½W resistor (RD14BB2B474J) (R54) on the foil side of the board from
connector 11 UP line to ground. (Unite before serial number 1119391).
If not already present, add a 470 Kohm ½W resistor (RD14BB2B474J) (R55) on the foil side of the board
connector 11 DOWN line to ground. (Unite before serial number 1119391).
Hard-wire the two via holes (through hole without components leads installed) along the foil trace between Q18
pin 1 and L1.
Change D1 from an ZX-060 (6V, 5%) to a WZ-040 (VII-4102-40) (4V, 10%) Zener.
Check D3 for leakage, which would load the MB line voltage below it normal 5.2 V DC setting.
RX unit X55-1270-xx
TR-7800: Change R94 from 56 ohm to 150 ohm ½W (RD14CB2E151J).
TR-7850: Change R94 from 100 ohm to 150 ohm ½W (RD14CB2E151J).
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.
Check D18 for leakage, loading the MB line.
With 13.8V DC applied to the radio, and the power switch OFF, adjust VR2 on
If memory loss persists after all changes and checks suspect control unit Q18 is defective.
the RX unit for 5.2V DC at connector 1, MB terminal.
We recommend using either Sanyo or GE NiCad Batteries.
We suggest not using Radio Shack or Eveready batteries in these radios.
Note:
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