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Old 19th Apr 2019, 6:27 pm   #1
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Default Sony KV-E2912U - won't turn on - AE-1A chassis

I'm trying to rescue a trinitron from 1990, I've had it randomly turn on before but not for ages now.

I was filthy when I got it but I cleaned it up, replaced a load of caps, replaced the LOPT, touched up the whole D board solder joints.

The standby LED usually flashes on and off, no pattern. Sometimes it doesn't, sometimes it flashes quickly, others slowly.

It always degausses and the heaters never glow.

Anyone got any ideas?
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Old 20th Apr 2019, 8:24 am   #2
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

A common fault with Sony receivers was a faulty/dry joints on the frame chip causing the symptoms you describe. If the chassis utilizes a chip [centre of chassis] it might be worth a check.
The 29" tube had a short life but let's hope your lucky. John.
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Old 20th Apr 2019, 10:12 am   #3
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

I'm pretty sure I'll have reflowed it already but I'll have a look. I know it has 3 circuit protectors in the HV section so might take a look at those too.

It's frustrating as when it did turn on the picture was lovely.
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Old 20th Apr 2019, 10:53 am   #4
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

if the heaters are glowing it means the power and line output sections are working. What happens if you turn the G2 up? If necessary ground one of the cathodes via a 22K resistor to see what happens on the screen.
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Old 20th Apr 2019, 11:58 am   #5
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

The heaters don't glow, only signs of life are the degauss and flashing standby LED
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Old 20th Apr 2019, 12:46 pm   #6
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

Bear in mind you very often need a head magnifier to find these dry,s.Sometimes just a crack across the joints.
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Old 20th Apr 2019, 1:59 pm   #7
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

I think some AE-1x versions (B and C, I'm not sure how similar their circuits are) had a high ohm resistor in the voltage divider for the +B regulation that went O/C. I don't remember the exact symptoms, though.
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Old 20th Apr 2019, 3:32 pm   #8
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

Not sure if it is relevant but a while ago I struggled with a Sony 29 inch set (can’t recall chassis type). This had all sorts of random faults from not coming out of standby to retuning itself to switching itself off. After a long saga I discovered that the I2C comms between the major chips was being corrupted by a spike protection zener on one of the bus lines. This was a 5v6 and was acting like around 3v3. Easy to check by looking at the idle state, once I twigged. The set had a small mains-5v smpsu which was on even in standby. Worth checking that too.
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Old 21st Apr 2019, 12:13 pm   #9
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

Check the soldering on any heatsinks too, these are used as chassis return links on this and some other chassis.
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Old 21st Apr 2019, 12:38 pm   #10
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

Ok so I've now:

Reflowed every solder point on the D board
Checked all high power resistors and all check out ok
Swapped out the large 400v block cap to no avail

Ive not checked zeners but then I don't have an idea where they might be. I can't find any circuit protectors either so I'm now questioning my schematics.

I did monitor standby HT though and it starts around 118v and gradually drops to about 116 after 15 minutes or so. Is this normal if the set is in protect? I can't get the standby light steady on with the remote (but it does work). Adjusting the standby HT pot I can only ever get it to about 131v at full turn.

Quote:
Originally Posted by Red to black View Post
Check the soldering on any heatsinks too, these are used as chassis return links on this and some other chassis.
Yeah already reflowed them all, I had the same thought.

Should I only be directing my attention to the D (main) board or should I be checking sub boards too? I have reflowed and changed caps on the neck card.
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Old 21st Apr 2019, 2:21 pm   #11
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

I have a fault list for this and other Sony chassis which maybe of some help, which I don't mind posting up later.
I have now been out of the repair game for about 10 years and my memory is not what it once was.
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Old 21st Apr 2019, 3:04 pm   #12
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

That would be incredibly helpful, thank you!
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Old 21st Apr 2019, 8:33 pm   #13
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

Have you checked that the low voltage lines are correct? A fault listing I have said flickering standby light was caused by the 5V line being low. Check Q604 which is in the power supply area.
I own a similar TV with the AE1 chassis and agree with the previous posters that fractured solder joints can be difficult to spot. I had problems with the picture size jumping and it was a bad connection to board J1.
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Old 21st Apr 2019, 9:38 pm   #14
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

I have and all DC voltage seems lower than it should be. Low voltage slowly rises but HT slowly drops over time. Neither are what they should be. Kinda suggests something transformer related maybe? Or voltage feeding it?
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Old 22nd Apr 2019, 9:58 am   #15
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

Well it randomly went into standby and the standby HT did indeed rest at 135v and found no low voltage. Coming out of standby goes back to our flashing led. After a while it's back to just flashing but it does seem to change as I'm moving things around. To be honest it really does feel like there's a dry joint somewhere but I don't think I've missed any?
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Old 22nd Apr 2019, 10:16 am   #16
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

I must have spent 50% of my life attempting to trace faults like this. Not such happy days. J.
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Old 22nd Apr 2019, 10:46 am   #17
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

I think I would try warming up sections of the pcb using a hairdryer. If there are capacitors with marginal performance you might find the set springs back to life. I would start in the PSU section. If all voltages are low it sounds like a fault on the primary side of the transformer, perhaps some of the components around the IC.
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Old 22nd Apr 2019, 11:01 am   #18
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

All Sony CRT TV's had an HT of 135V
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Old 22nd Apr 2019, 4:24 pm   #19
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

It does when it randomly decides to enter standby. As soon as it tries to switch on it drops to about 118v.

I've now swapped (from a known good chassis):

Q609
D601
C818
IC502
T802
C604
IC601
D612
D910
C613
PS601 + PS602 tested ok

I can't find any components which read strangely. It just worries me that it never even tries to start the tube now when it did when turn on now and then when I first got it.
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Old 22nd Apr 2019, 4:36 pm   #20
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Default Re: Sony KV-2912U - won't turn on - AE-1A chassis

Here is a list of faults for that chassis, see attached.
Ps. that list was not compiled by me so I cannot verify the accuracy of any information contained within it, use at own risk etc..etc.
It might help still
Attached Files
File Type: txt Sony AE1 Fault list.txt (10.9 KB, 681 views)
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Last edited by Red to black; 22nd Apr 2019 at 4:39 pm. Reason: ps. added
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