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Crumbtrail TV Forums: TV Equipment: TV Repair Forum:
RCA - Sound, no high voltage

 

 


herman2003
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May 12, 2003, 3:47 PM

Post #1 of 1 (2492 views)
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RCA - Sound, no high voltage Can't Post

I have a RCA model F25432 (CTC203AD5) that has sound no picture. I seem to have about half the voltages that are derived from the autotransformer T14401. Mainly, the low voltages up to 130 volts.

I have some sound, no picture. Putting a scope on the video IF IC, I have the horizontal output signal. Even up to the horizontal drive transistor, I have the 230 volt waveform signal on the collector. From there it goes through a transformer, T14301 and on to the base of the horizontal output transistor HOT (Q14401). I do not have the the 16 volt p-p signal on the base of the HOT. I checked the transformer and components between the horizontal drive transistor and horizontal output transistor. However, the waveform is not present at the base of the HOT. I am suppose to have a -.07 volt on the base of the HOT and 130 volts on the collector. I have -.021 on the base and 138 volts on the collector of the HOT. At this point I am not sure if the HOT is bad or the flyback transformer is bad. On the schematic symbol of the HOT, it shows an internal resistor between the base and the emiter and an internal diode across the emitter to collector. My B&K transistor checker showed that it was good in the circuit testor mode. However, testing the HOT in the circuit, it showed the NPN transistor as both PNP and NPN and showed it was good. Perhaps, I should take it out of the circuit and test it.

Lastly, I can't verify if the fly back is good without a flyback tester. I do not have the 24-26kv voltage on the secondary of the flyback transformer T14401. Apparently, the primary side winding (pins 2 to 10) have conductivity, because the 138 volts is supplied to pin #2 and pin #10 of the flyback transformer is the source to the collector of the HOT> Not sure where to go from here. Thanks for any assistance.


 
 
 


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