Must be a 12 volt car radio? Voltages are low because input is probably lower than expected.
Don't have a schematic but check output transistor. Might be large diamond shape? If it is there will also be a current adjustment. Small metal with screwdriver slot. These can make poor contact over time.
Norm
:I have an Automatic CTP-5071, MT-5073, MUS 5059 auto radio which I am trying to restore. The dial lamp lights, but I have no audio at all. The source voltages are way down, between -.5 volts to -1.5 volts, where they should be 8.8V, 10.2V and 12.4V. I have replaced all the caps but the problem persists. I am lost.........What do I try next?
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SIR Reed . . . .
O.K here is your working-mark-up schematic for same. All of the electrolytics are boxed in [ FUSCIA] and the first unit to ascertain integrity of would be the ½ ohm 1 watt “confusible” resistor in the emitter leg of the output transistor.[YELLOW BOX]
If it is open, the output transistor would be suspect, pull and do a resistance check from emitter to collector, in the low decades of resistance or even lower would signify a bad unit. Other replacement options have been listed, for other like Germanium PNP power category of transistors in the TO-3 casing profile. Do note that a mica insulator is required between the case / collector and the heat sink. Liberally sopped in bacon grease . . .or MORE preferrably . . . silicone grease.
If it happens to be bad, you could then leave it out of circuit and evaluate the rest of the receiver by the placing of a 5 ft length of wire into the antenna connector . . .a la . .antenna, and then monitor the collector to ground of the X4 driver transistor with metering in AC low voltage range.
Then as you slowly tune into a station, you should see the meter respond to the AF modulation and then drop off, as tuned off from the station. This is certainly easier to see on an analog type of metering, or in the digital category if you happen to have a FLUKE which additionally has a fast responding set of ~100 linear bar graph - hash marks on its LCD display.
Your voltages given didn’t mean much to me, as per most likely being for the output transistor, but there were no voltages being up in the 12 or 8 volt level categories. Thus the nagging suspicion of that .5 ohm being BLOWN wide open.
Waiting for driver and output voltage readings, just in case you don’t nail it right off the bat.
Standing by for feed back . . . .
73's de Edd
