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3Phase615V · 20th Oct 2019, 9:28 pm

Hi,

I have owned and used, almost daily, a very reliable Hitachi C1714TE 17" colour TV for 22 years. However, for the first time ever it's failed to switch on fully and won't budge out of standby. With this particular TV, the red power-on/standby LED lights brightly when in standby then dimly when the set is turned on, so as not to be a distraction during TV viewing I guess. Anyway, on switching on the TV power button, I can hear for about a second, as it normally does, the tube static crackle, but then nothing. At the same time the TV is powered on, the standby LED lights dimly during the static charge but then glows brightly to indicate the TV has switched to standby. In this state neither the TV remote nor the built-in channel up/down buttons bring the TV on as they should.

So with that, I found the TV's service manual online (C1714TE Service Manual) and took a few voltage measurements. As expected with there being standby power, on the primary side, I found just over 300V-AC at the collector of Q903 (ON4584/BUT12AF) but that the base of Q903 doesn't connect via R918 (not installed) to the collector of Q902 but instead goes directly to the emitter of Q901. This can be seen by comparing the schematic to the track side image (see attached). Also the transistors stated for Q901 (2SA1390C/D) and Q902 (BC368) in the schematic don't match the ones installed in my TV, with Q901 being a JC558B and Q902 being a 2SC368. I check the stated SM voltages on Q901/2 and found they did not really match the stated values, but as I have standby power I've assumed they must be okay.

So moving on to the secondary side, I checked the output voltages on T901 and found the cathode side of D951 (S1) to have 117VDC and the cathode side of D852 (S3) to have 14.1VDC. I guess with these voltages I can at least assume I have a good power supply but I am not sure of how the standby circuit works here so I am in need of some guidance and pointers on what to test next as clearly something is blocking the power-up sequence.

Any advice gratefully received.

Here are my voltage test results.

Q903
B: 0 V
C: 318 V
E: -2.14 V

Q902
B: -2.7 V
C: -2.38 V
E: -2.0 V

Q901
B: -0.6 V
C: -0.645 V
E: 0 V

D951 cathode: 117 V
D952 cathode: 14.1 V

Cheers!

20th Oct 2019, 9:28 pm	#1
3Phase615V Tetrode Join Date: Nov 2011 Location: London, UK. Posts: 90	Hitachi C1714TE stuck in standby Hi, I have owned and used, almost daily, a very reliable Hitachi C1714TE 17" colour TV for 22 years. However, for the first time ever it's failed to switch on fully and won't budge out of standby. With this particular TV, the red power-on/standby LED lights brightly when in standby then dimly when the set is turned on, so as not to be a distraction during TV viewing I guess. Anyway, on switching on the TV power button, I can hear for about a second, as it normally does, the tube static crackle, but then nothing. At the same time the TV is powered on, the standby LED lights dimly during the static charge but then glows brightly to indicate the TV has switched to standby. In this state neither the TV remote nor the built-in channel up/down buttons bring the TV on as they should. So with that, I found the TV's service manual online (C1714TE Service Manual) and took a few voltage measurements. As expected with there being standby power, on the primary side, I found just over 300V-AC at the collector of Q903 (ON4584/BUT12AF) but that the base of Q903 doesn't connect via R918 (not installed) to the collector of Q902 but instead goes directly to the emitter of Q901. This can be seen by comparing the schematic to the track side image (see attached). Also the transistors stated for Q901 (2SA1390C/D) and Q902 (BC368) in the schematic don't match the ones installed in my TV, with Q901 being a JC558B and Q902 being a 2SC368. I check the stated SM voltages on Q901/2 and found they did not really match the stated values, but as I have standby power I've assumed they must be okay. So moving on to the secondary side, I checked the output voltages on T901 and found the cathode side of D951 (S1) to have 117VDC and the cathode side of D852 (S3) to have 14.1VDC. I guess with these voltages I can at least assume I have a good power supply but I am not sure of how the standby circuit works here so I am in need of some guidance and pointers on what to test next as clearly something is blocking the power-up sequence. Any advice gratefully received. Here are my voltage test results. Q903 B: 0 V C: 318 V E: -2.14 V Q902 B: -2.7 V C: -2.38 V E: -2.0 V Q901 B: -0.6 V C: -0.645 V E: 0 V D951 cathode: 117 V D952 cathode: 14.1 V Cheers!