Sony Trinitron no picture, sound OK


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Sony Trinitron no picture, sound OK

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Michael G
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Jul 8, 2005, 3:31 PM

Post #1 of 10 (3625 views)
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Sony Trinitron no picture, sound OK	Can't Post

Hi everyone,

I read several messages on the forum with similar problems, but it seems that I have something different. The picture disappeared yesterday evening on a about 10 year old 32XBR45 TV. Filament looks okay, increased screen output on the CRT board, but saw bright green screen with retrace lines that were not filling the entire screen horisontally, but showed pincussion effect, while the entire screen was bright. I immediately turned the brightness down. Shorting the filament limiting resistor ( R704, per Mel's advice) gave similar results, but at a lower screen output.

Please advice what could be potential problems and how do I fix them. I have a multimeter and a scope. Thank you.

mel
Veteran

Jul 8, 2005, 10:44 PM

Post #2 of 10 (3611 views)
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Re: [Michael G] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

Check to see if you have about 150 vdc on pin 11 of the CRT. If not, check for a short between pins 11 and 8 and post back with results.

Michael G
New User

Jul 8, 2005, 11:17 PM

Post #3 of 10 (3609 views)
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Re: [mel] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

Hi Mel,

Thank you for replying. I have about 205 V dc on pin 11 and there is ~ 4.6 M ohms between pins 11 and 8

mel
Veteran

Jul 9, 2005, 6:02 AM

Post #4 of 10 (3602 views)
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Re: [Michael G] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

OK, the CRT isn't shorted. The closest info that I have to your model is a 32XBR48 but I am assuming that it is basically the same circuitry. Check the voltage on pins 10 and 12 also to see if they are at about 200 vdc. If so, check Q1761 and D1767. Next check for 9 vdc on pin 2 of IC1761/2/3. If those are good, you probably have a failed jungle IC.

Michael G
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Jul 9, 2005, 1:28 PM

Post #5 of 10 (3597 views)
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Re: [mel] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

Thanks again Mel. The voltages are the same on pins 10, 11 and 12 at about 205 V dc. However I can not find the components you mentioned on the CRT board. Numbers on the CRT bd are in the 7XX range, but there is no 761 or 767. Could you please guide me which board are they on. Thanks.

mel
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Jul 12, 2005, 1:16 AM

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Re: [Michael G] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

OK I'm back with the correct schematic. Have you checked the voltages on the transistors in the video circuit (e.g. Q317, Q722, Q721 and Q772)? Since all three guns are cut off by the high voltage on the cathodes, I'm looking for something that is common to all three paths and the one thing that I do see is the 9 vdc from the power supply. Also common is Q770 and its related components. Also check for proper voltage at pin 25 of the jungle IC. If everything checks out OK. it is probably the jungle IC

Michael G
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Jul 12, 2005, 2:57 AM

Post #7 of 10 (3561 views)
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Re: [mel] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

Hi Mel,

A can not fine the common problem with video output. I thought it is D777, replaced it with 4.3V zener, but still have practically zero V across it. All DC voltages appear to be fine, I got 9, 200, and 1kV. I do not think that Q770 can hold all cathodes at 205 Vdc.

The Jungle IC is puzzling me. I have nice AC and DC signal on pin 1, almost picture perfect as per schematic, however, the signal on pin 3 looks different than on schematic. I do not know the role of this signal. I also do not have any video outputs on pins 22, 23, and 24, while I do have almos proper DC voltage on pin 25.

While adding the screen voltage I can see that I do have video signal on the screen, which contradics the jungle IC output that I observed.

Overall , I do not know what to think and what to try next. Looking forward for your advise.

mel
Veteran

Jul 12, 2005, 5:21 AM

Post #8 of 10 (3560 views)
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Re: [Michael G] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

Pin 1 is the video and pin 3 is the color component. A friend recently had a similar situation and said that after he changed the switching IC, he was back with a picture but it was washed out so he also changed the jungle IC which brought the set back to working normal. It was a different model but I think that the principal is the same. You do have two buffer transistors between the IC and jungle so scope pin 45 of the switching IC next

Michael G
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Jul 25, 2005, 2:19 AM

Post #9 of 10 (3424 views)
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Re: [mel] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

Kudos to Mel,

Your original intuition and experience were right on the money. It was the jungle IC. According to the schematics, it had the right input, but the wrong output. I changed it today and TV is back to normal.

Mel, thank you very much for your help and advice.

Kind Regards,

Michael

mel
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Jul 25, 2005, 10:37 PM

Post #10 of 10 (3407 views)
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Re: [Michael G] Sony Trinitron no picture, sound OK [In reply to]	Can't Post

Yer welcome. Glad it worked out.

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