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Old 13th Nov 2019, 9:29 am   #61
Michael Maurice
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Default Re: Sony KV-E2912U AE-1A Chassis - Part 2

This is a classic symptom of a worn CRT, what happens if you increase the A1/G2 control?
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Old 13th Nov 2019, 10:38 am   #62
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Default Re: Sony KV-E2912U AE-1A Chassis - Part 2

AKB circuit. Usually one of the guns is lower emission, and the set blanks the picture at start up - there is an IK detect line feeding this info back to the mainboard. The picture usually flashes a bit before returning fully.

There are various tweaks you can do but in my case I never had one that then worked longer than another six months or so.
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Old 13th Nov 2019, 2:38 pm   #63
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Default Re: Sony KV-E2912U AE-1A Chassis - Part 2

I have raised the heater voltage slightly in the past to get around this issue with a worn Trinitron CRT. It works but as ben says it only buys you some time.
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Old 13th Nov 2019, 3:48 pm   #64
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Default Re: Sony KV-E2912U AE-1A Chassis - Part 2

Of all the brands of TV I might be tempted to rescue, late 80s Sony is the least tempting for this reason! Plus, they're damn heavy too...

I think the only large screen Sony I have is a KV2730, the one with detachable speakers, circa 1984. No idea if that chassis suffers from AKB symptoms. Must dig it out...
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Old 14th Nov 2019, 11:22 am   #65
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Default Re: Sony KV-E2912U AE-1A Chassis - Part 2

I was dreading this being the case. I forgot the symptoms so wasn't sure. IIRC this was a common issue with 29" sets, some only a few months old so I suppose it's done well. Easily the best Trinitron I've had but I guess time to start looking for another.

Thanks for the help guys.
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Old 14th Nov 2019, 11:25 am   #66
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Default Re: Sony KV-E2912U AE-1A Chassis - Part 2

Actually, would having adjusted the screen volts on the neck board cause this if set too high/low? I did make some adjustments when I last had it open and to be fair it seemed to coincide with this now that I think about it.

In fact, I believe tweaking this pot actually got it to fire up. Bad pot maybe? Most on this set seem to be iffy in some way or another.
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Old 14th Nov 2019, 12:11 pm   #67
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Default Re: Sony KV-E2912U AE-1A Chassis - Part 2

Trust the A1 res and diode are ok?
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Old 14th Nov 2019, 2:30 pm   #68
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Default Re: Sony KV-E2912U AE-1A Chassis - Part 2

Quote:
Originally Posted by Retrorepair View Post
Actually, would having adjusted the screen volts on the neck board cause this if set too high/low? I did make some adjustments when I last had it open and to be fair it seemed to coincide with this now that I think about it.

In fact, I believe tweaking this pot actually got it to fire up. Bad pot maybe? Most on this set seem to be iffy in some way or another.
The pot doesn't need to be bad for those symptoms. Just turn it up slightly and see of the symptoms improve. If you turn it up and get flyback lines, turn it back slowly until the flyback lines disappear.
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Old 14th Nov 2019, 3:07 pm   #69
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Default Re: Sony KV-E2912U - won't turn on - AE-1A chassis

I would add to Maarten's valid comment that you may find that you increase the G2, then back it off when the retrace lines appear, getting an acceptable picture...only to find the next time you switch on you are back to square one! So don't back it off too much.

At the end of the day, all these tweaks to the heater and screen settings are best seen as temporary workarounds. Just enjoy it as long as you can and keep looking for another set (not a Sony of this vintage!)
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Old 14th Nov 2019, 5:14 pm   #70
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Default Re: Sony KV-E2912U - won't turn on - AE-1A chassis

The only reason I touched the screen pot at all was due to the red bleeding. Turning it down corrected the issue (there is no adjustment for red drive). Could this mean something is driving the red too hard which is what's causing the odd AKB voltage? Or adjusting down just highlighted the start of the degradation maybe.

I honestly just wanna make sure I've ruled out every possibility
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Old 14th Nov 2019, 8:19 pm   #71
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Default Re: Sony KV-E2912U - won't turn on - AE-1A chassis

Colour bleeding due to cathode wear is usually solved by turning up the G2 voltage instead of turning it down..

Bleeding can also occur when the supply voltage for the cathode drivers is too low or has too much ripple as it is the result of the drivers being driven into saturation which the AKB circuit will do if the feedback is too low.
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