开云体育

I've done some additional wire tracing and I believe I may have found
the overheated resistor on the TR3 schematic. From my wire tracing
in the TR3, Pin 11 on the rear power connector is the +250VDC power
supply voltage. Pin 11 connects to R111. R111 connects to the positive
terminal of C145B, 60ufd 250VDC capacitor, one of the 2 capacitors in
the only can capacitor in the TR3.

I've found a picture of the underside of a TR3 and the color band of the
overheated resistor are ORANGE ORANGE RED SILVER which is 3.3K 10%
and it's a 1/2W resistor.

If C145B shorts to ground under voltage then that could cause R111,
3.3K 1/2W resistor to overheat. This would short out the +250VDC rail
causing loss of receiver function, no audio, etc.

If my Ohms Law math is correct, a shorted C145B would cause 75ma
of current to flow through R111 at a power level of 18W.

I = E / R
"E" is 250
"R" is 3300

250 / 3300 = 0.075 amps (75ma)

0.075 x 0.075 x 3300 = 18W

I have measured continuity from one lead of the overheated resistor to
pin 11 on the rear power connector and see continuity. I measured
continuity from the other overheated resistor lead to C145B and found
continuity. Using an ohm meter doesn't show C145B shorted but that's
because the battery voltage is too low to measure the short in C145B.
Under +250VDC C145B could easily short causing R111 to overheat and
loss of +250VDC voltage to other circuits.

I have a few more measurements to take to be sure then I'll have to replace
C145 can capacitor.

73
Mike W5RKL