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Old 24th Sep 2022, 9:25 pm   #1
Zuofu_C
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Default RCA 24F650T (Thomson ITC-008 chassis) relay clicking/power cycling but no image

Hi All,

I've got a RCA 24F650T, that I've done a fair bit of work on, including dumping the EEPROM and installing a socket for the EEPROM, but recently I've got an issue which is baffling. So issue started with the TV refusing to power on, I will turn it on, it will click (I can hear the screen energize) and then it will flash white for a split second, and then turn off - upon which time it will restart. I've disassembled the screen and tried reprogramming the EEPROM with my known working .BIN with no avail.

I did notice that if I remove the EEPROM completely and power up the TV, it will start in the menu with some random settings for a couple of seconds, upon which time it will shut off (and then go back into the same power cycle loop). I'm going to try to replace the EEPROM (a new one is coming in tomorrow), but I was also thinking if you had any ideas. I'm also planning on putting my oscilloscope on the I2C lines, in case the I2C lines are being pulled high/low somehow (though I'm not sure how).

Is there anything on the analog side that you would recommend checking? I've attached the datasheet for the chassis, the visual inspection of the PCB looks pretty good, no obviously leaking capacitors. My particular TV has a separate PCB for the East-West drive, which I don't seem to have the schematics for.
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File Type: pdf THOMSOM ITC008.pdf (1.25 MB, 46 views)
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Old 25th Sep 2022, 11:25 am   #2
Ambientnoise
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Default Re: RCA 24F650T (Thomson ITC-008 chassis) relay clicking/power cycling but no image

I am not a tv person but your mention of I2C lines reminded me of a long struggle with a Sony set. I didn’t have a scope at the time but managed to ascertain that the I2C was misbehaving but which of several chips could be responsible? Turned out to be a (spike protection ?) zener on the line which had gone partial short (3v ish rather than 5v6) leading to indeterminate logic states. Worth a check.
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Old 25th Sep 2022, 12:09 pm   #3
Welsh Anorak
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Default Re: RCA 24F650T (Thomson ITC-008 chassis) relay clicking/power cycling but no image

Not familiar with this model, but we did have problems with some of the late Thomsons that would trip the set if the CRT was tired and took too long to reach full emission.
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Old 25th Sep 2022, 10:40 pm   #4
Zuofu_C
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Default Re: RCA 24F650T (Thomson ITC-008 chassis) relay clicking/power cycling but no image

Quote:
Originally Posted by Ambientnoise View Post
I am not a tv person but your mention of I2C lines reminded me of a long struggle with a Sony set. I didnít have a scope at the time but managed to ascertain that the I2C was misbehaving but which of several chips could be responsible? Turned out to be a (spike protection ?) zener on the line which had gone partial short (3v ish rather than 5v6) leading to indeterminate logic states. Worth a check.
Thanks for the reply. I just did some checks with the oscilloscope, and the I2C waveforms look fine (clean, sharp transitions, no weird looking/floating logic levels. Also, I noticed that the Zener clamp diodes aren't even installed on my set DR011/DR012. I also replaced the I2C EEPROM and flashed it to the known working but I'm getting the same error.
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Old 25th Sep 2022, 10:50 pm   #5
Zuofu_C
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Default Re: RCA 24F650T (Thomson ITC-008 chassis) relay clicking/power cycling but no image

Quote:
Originally Posted by Welsh Anorak View Post
Not familiar with this model, but we did have problems with some of the late Thomsons that would trip the set if the CRT was tired and took too long to reach full emission.
Thanks for the reply...yes that's certainly possible. The set has a lot of hours in it (it was my primary retro-gaming set), at least I feel less bad retiring it if that's in fact the reason
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Old 27th Sep 2022, 3:07 am   #6
Zuofu_C
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Default Re: RCA 24F650T (Thomson ITC-008 chassis) relay clicking/power cycling but no image

I've fixed it! The fact that the TV works (for a little while) with no EEPROM installed gave me a big hint: so even though the I2C was working correctly when probed, I still had my suspicions since it seemed like a software/firmware issue. Upon further inspection, I found the following on the external "debug" connector, the 4 pin debug connector (which I had been using to tap the I2C bus) has cracked from the stress of being connected to an external device.
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