R-1715/TRC-87A Military UHF Receiver

©Brooke Clarke, N6GCE

Front

Bottom

Bottom cover removed

Description

This is a 5" high rack mount Military UHF radio receiver made by Motorola for the Air Force. All connections are on the front panel. The 19 pin connector is labeled 120/208 Volts, 400 CPS, 3 Phase 4 wire. My plan was to replace the 400 Hz supply with a 60 Hz Power Supply brick which would fit in the right rear empty space behind the three synthesizer modules. Never did make the conversion.
The synthesized tuning covers from 220.00 to 399.95 MHz. In addition there is a triple cavity preselector that is tuned by the manual geared tuning knob whose dial is calibrated with 5 MHz ticks. This receiver was designed to work with a transmitter very close by. Solid state construction using mostly discrete components (the golden age of surplus) should make it repairable.
Power Supply A7
Power Supply connector J108 is a D type with 15 pins, 10 of which are used and 5 are n.c.

The 4 solid colors White, Gray, Purple and Green come from the front panel connector and On-Off switch.

The 2 White-Blue-Red striped wires come out of the power supply and go to terminal E102. (probably 18 VDC)

The 3 White-Red striped wires come out of the power supply and go to terminal E104. (Probably 24 VDC)

The 1 Black wire goes to Ground.

This implies that there are only two power supply voltages used. The E102 and E104 terminal posts are located just behind the 4 each tublar 400 Hz power line filters. The Front panel meter switch has positions for 18 Volts and for 24 Volts. The rear wiper on the meter switch connects to E104 in the 28 Volt position and to E102 in the 18 Volt position.
The main power transformer has a circuit diagram showing a "Y" input (Gray, Purple & White) including a common (Green) wire, and a "Y" secondary (without a common wire) with the rating 21 Vrms L-L @ 3.5 Amps. So the total power supply load current should not exceed 3.5 Amps DC.
The A7 Power Supply module can easily be removed by loosening two screws on the side of the receiver and pulling it up and out of the chassis.

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