Sony KV-E2912U - won't turn on - AE-1A chassis - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Welsh Anorak · 25th Apr 2019, 4:20 pm

Good grief - you've nearly rebuilt the TV! Maarten's spot on here - most of those parts will have been OK and it's so easy to introduce aditional faults when blanket changing - we've all done it.
The voltages you have measured appear to be on the transformer's pins which will make no sense. You need to measure the DC voltages AFTER the respective rectifiers.Disregard the heater voltage, but are the tube heaters actually glowing?
Let's get back to basics. Do you have 135v when the line stage is disconnected and the PSU is loaded by a bulb? If so you can be confident of a line output fault or a low resistance in a fed line. If you are getting voltages 'south' of the rectifiers then it's fair to assume the output stage is working to some extent, though the output transistor will be getting warm.
Narrow down the area in trouble then we can start testing components.
If the original transformer was grey and made in Slovakia then in the bin it goes! Putting it back might cause more parts to fail.

Retrorepair · 25th Apr 2019, 7:21 pm

Of course your both right, it's a classic wxample of being lazy and making more work for myself.

The low voltages I posted were all taken from points marked on the board as 12v, 5v etc. Mostly daughter boards so definitely after rectification. The HT was taken from the test point. When it's in standby it's a steady 135v but when it's trying to turn on and the standby led flashes it drops to about 118v. No low voltages are present until it tries turning on and all are about half what they should be.

I've not worked on a monitor with no HT before, I work more with low voltage electronics but repaired my share of them. I've seen the lightbulb test before but never needed to try it so not sure what to do.

It seems to me maybe something's gone slightly short and is sinking some of that voltage. Just need to understand what area to work from, though knowing more about these chassis would help. Is there any recommended reading for TV chassis working theory?

The chopper is a large blue potted block so I'll leave it where it is

Michael Maurice · 25th Apr 2019, 7:58 pm

Quote:

Originally Posted by Welsh Anorak

If the original transformer was grey and made in Slovakia then in the bin it goes!

That really only affecting later sets, late 1990’s, early 2000’s

Maarten · 25th Apr 2019, 9:04 pm

If the 0V on the 27V line was indeed measured after rectification, first thing I would do is stick a multimeter on diode test between +27 and ground (set switched off) and look for a low reading (positive test lead on +27 line). Then, starting at the rectifier and working away from the line output transformer, see which component causes the low reading. If there isn't a low reading, the fault could be elsewhere. I'll look for a schematic in the meantime.

The lamp test is in this case, disconnecting the +135V line from the line output stage and put a 75W light bulb between +135V and ground. If it measures 135V while powering the light bulb, the power supply is probably working correctly.

P.S. Maybe a moderator could update the subject line to reflect the correct model number KV-E2912U (see #30)?

Retrorepair · 26th Apr 2019, 4:15 pm

27v doesn't seem to measure too low on diode test anywhere down the line that I can see.

Ok, so at which point should I disconnect 135v and put my bulb?

Retrorepair · 26th Apr 2019, 4:49 pm

Quote:

Originally Posted by Welsh Anorak

The voltages you have measured appear to be on the transformer's pins which will make no sense. You need to measure the DC voltages AFTER the respective rectifiers.Disregard the heater voltage, but are the tube heaters actually glowing?

Only the 27v was measured from the transformer pins, the rest were taken from points labled 12v or 5v etc.That said, I get the same 0v on a pin labled 27v too.

The heaters are not glowing. There's no sign either that I'm getting HT.

I measured right on Q604 (5v regulator) and in standby it measures 6v but when it's trying to turn on/flashing led, it drops to about 3.5v

Retrorepair · 28th Apr 2019, 3:02 pm

I've gone through every resistor on the board to check their values are correct and while I've found and replaced a couple that were a bit off, no change at all. All the diodes seem fine and I think I've replaced already all the major components.

Is it at all common for the chopper tx to fail? This one is a large blue potted unit. I hope not as I can't even find refrence to it's existence online, let alone a replacment.

By this point I'm out of ideas. Anyone near Essex fancy looking at it for me? Will pay good money to get this thing working.

Retrorepair · 28th Apr 2019, 4:48 pm

Ok well substantial update, got it to turn on! Trouble is, it ONLY turns on when I have my multimeter probing the collector of Q607. Now as I've already replaced this AND already replaced D610, I'm wondering what is at fault. D624? D271?

Retrorepair · 28th Apr 2019, 5:01 pm

Ok well now it just seems to come on regardless. 100% sure probing that pin made a difference, unless I accidentally shorted two pins and it's brought something back to life? It does seem to be having a vertical deflection issue where the image is rapidly shrinking and wxpanding vertically but this was an issue when it turned on when I first got it too so somehow, all the parts I've changed have made no difference at all!

So while I'm happy I've not made it worse, I'm confused what could even now be the problem.

HamishBoxer · 28th Apr 2019, 5:15 pm

And you have reworked the pins on frame ic?Plus the regulators that go dry jointed?

Retrorepair · 28th Apr 2019, 5:23 pm

I've reworked every single point on the D board.

HamishBoxer · 28th Apr 2019, 5:25 pm

Of course or did you change the frame ic itself?

Another long shot is,the feed res normally a safety res, that feeds the diode that supplies the frame voltage is intermittent.

Retrorepair · 28th Apr 2019, 5:51 pm

Yeah I changed it for a parts board IC. I have a new TDA8172 here, would that work instead of the 8170?

I'll check that resistor. The image does stabalize after a while, but if it's exactly the same problem as before, it'll destabilise again and shut down after 5 mins or so then we will be back to a flashing led.

Maarten · 28th Apr 2019, 6:14 pm

Given those new symptoms, chances are there's a loose connection somewhere in the vicinity of where you had to probe to start the set up. Maybe not a loose soldering connection if you redid them all, but rather a hairline fracture in a copper track.

Retrorepair · 28th Apr 2019, 6:49 pm

That sounds entirely feasible given that is was only after pulling the chassis for cleaning that it wouldn't even try to turn on anymore.

I also measured the HT while it was on and it was fluctuating between 136 and 138v. Possibly as if there's a fracture it's only just making connection so whilenit looks like a deflection issue it could well be shutting down and powering up rapidly.

HamishBoxer · 28th Apr 2019, 7:34 pm

Are is there an HT pot?(Intermittent)

Retrorepair · 28th Apr 2019, 8:41 pm

There is but I've not been near it, worth checking out though

davyrocket2 · 29th Apr 2019, 8:34 pm

I suggest having a very careful look around the area you placed the probe and look at each contact and find the other end to see if it has continuity there could be crack or a break that is too small too be visible

Retrorepair · 7th May 2019, 7:17 am

Continuity from Q607 to the end of those traces seems fine, no cracks in traces to my eye and now the TV stays on most of the time. After 20 minutes or so it will shut down but then power right back up for another 20 minutes or so. It's all very random and I do suspect there is a cracked trace but where it is I don't know. I'll come back to this thread if I have any updates.

One thing I will say is this thing runs hot, it's no wonder there's so many heat related issues on these sets. I'm gonna install a silent fan in the upper case to extract some of the heat I think, maybe give it a bit more lifespan.

Retrorepair · 13th Nov 2019, 9:11 am

Hey guys, I'm back with more issues with this set!

So I finally got it to work reliably by reflowing all the daughter boards and it was fine for months but now I've a new issue.

The set turns on fine and the neck glows happily but no image on screen, not even the OSD. If I leave it half hour it will finally show an image and stay that way until I turn it off but when I do, same thing.

If I tweak the V size pot I can see the top raster so it is on but it seems the blanking isn't letting the image show. Does anyone know how I can disable this so I can see what's going on when I start it up? I'm guessing it's not a stable raster?

25th Apr 2019, 4:20 pm	#41
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,916	Re: Sony KV-2912U - won't turn on - AE-1A chassis Good grief - you've nearly rebuilt the TV! Maarten's spot on here - most of those parts will have been OK and it's so easy to introduce aditional faults when blanket changing - we've all done it. The voltages you have measured appear to be on the transformer's pins which will make no sense. You need to measure the DC voltages AFTER the respective rectifiers.Disregard the heater voltage, but are the tube heaters actually glowing? Let's get back to basics. Do you have 135v when the line stage is disconnected and the PSU is loaded by a bulb? If so you can be confident of a line output fault or a low resistance in a fed line. If you are getting voltages 'south' of the rectifiers then it's fair to assume the output stage is working to some extent, though the output transistor will be getting warm. Narrow down the area in trouble then we can start testing components. If the original transformer was grey and made in Slovakia then in the bin it goes! Putting it back might cause more parts to fail. __________________ Glyn www.gdelectronics.wales

25th Apr 2019, 7:21 pm	#42
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis Of course your both right, it's a classic wxample of being lazy and making more work for myself. The low voltages I posted were all taken from points marked on the board as 12v, 5v etc. Mostly daughter boards so definitely after rectification. The HT was taken from the test point. When it's in standby it's a steady 135v but when it's trying to turn on and the standby led flashes it drops to about 118v. No low voltages are present until it tries turning on and all are about half what they should be. I've not worked on a monitor with no HT before, I work more with low voltage electronics but repaired my share of them. I've seen the lightbulb test before but never needed to try it so not sure what to do. It seems to me maybe something's gone slightly short and is sinking some of that voltage. Just need to understand what area to work from, though knowing more about these chassis would help. Is there any recommended reading for TV chassis working theory? The chopper is a large blue potted block so I'll leave it where it is

25th Apr 2019, 9:04 pm	#44
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Sony KV-2912U - won't turn on - AE-1A chassis If the 0V on the 27V line was indeed measured after rectification, first thing I would do is stick a multimeter on diode test between +27 and ground (set switched off) and look for a low reading (positive test lead on +27 line). Then, starting at the rectifier and working away from the line output transformer, see which component causes the low reading. If there isn't a low reading, the fault could be elsewhere. I'll look for a schematic in the meantime. The lamp test is in this case, disconnecting the +135V line from the line output stage and put a 75W light bulb between +135V and ground. If it measures 135V while powering the light bulb, the power supply is probably working correctly. P.S. Maybe a moderator could update the subject line to reflect the correct model number KV-E2912U (see #30)? Last edited by Maarten; 25th Apr 2019 at 9:12 pm.

26th Apr 2019, 4:15 pm	#45
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis 27v doesn't seem to measure too low on diode test anywhere down the line that I can see. Ok, so at which point should I disconnect 135v and put my bulb? Last edited by Retrorepair; 26th Apr 2019 at 4:39 pm.

28th Apr 2019, 3:02 pm	#47
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis I've gone through every resistor on the board to check their values are correct and while I've found and replaced a couple that were a bit off, no change at all. All the diodes seem fine and I think I've replaced already all the major components. Is it at all common for the chopper tx to fail? This one is a large blue potted unit. I hope not as I can't even find refrence to it's existence online, let alone a replacment. By this point I'm out of ideas. Anyone near Essex fancy looking at it for me? Will pay good money to get this thing working.

28th Apr 2019, 4:48 pm	#48
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis Ok well substantial update, got it to turn on! Trouble is, it ONLY turns on when I have my multimeter probing the collector of Q607. Now as I've already replaced this AND already replaced D610, I'm wondering what is at fault. D624? D271?

28th Apr 2019, 5:01 pm	#49
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis Ok well now it just seems to come on regardless. 100% sure probing that pin made a difference, unless I accidentally shorted two pins and it's brought something back to life? It does seem to be having a vertical deflection issue where the image is rapidly shrinking and wxpanding vertically but this was an issue when it turned on when I first got it too so somehow, all the parts I've changed have made no difference at all! So while I'm happy I've not made it worse, I'm confused what could even now be the problem.

28th Apr 2019, 5:15 pm	#50
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,931	Re: Sony KV-2912U - won't turn on - AE-1A chassis And you have reworked the pins on frame ic?Plus the regulators that go dry jointed? __________________ G8JET BVWS Archivist and Member V.M.A.R.S

28th Apr 2019, 5:23 pm	#51
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis I've reworked every single point on the D board.

28th Apr 2019, 5:25 pm	#52
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,931	Re: Sony KV-2912U - won't turn on - AE-1A chassis Of course or did you change the frame ic itself? Another long shot is,the feed res normally a safety res, that feeds the diode that supplies the frame voltage is intermittent. __________________ G8JET BVWS Archivist and Member V.M.A.R.S Last edited by HamishBoxer; 28th Apr 2019 at 5:49 pm.

28th Apr 2019, 5:51 pm	#53
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis Yeah I changed it for a parts board IC. I have a new TDA8172 here, would that work instead of the 8170? I'll check that resistor. The image does stabalize after a while, but if it's exactly the same problem as before, it'll destabilise again and shut down after 5 mins or so then we will be back to a flashing led. Last edited by Retrorepair; 28th Apr 2019 at 6:09 pm.

28th Apr 2019, 6:14 pm	#54
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Sony KV-2912U - won't turn on - AE-1A chassis Given those new symptoms, chances are there's a loose connection somewhere in the vicinity of where you had to probe to start the set up. Maybe not a loose soldering connection if you redid them all, but rather a hairline fracture in a copper track.

28th Apr 2019, 6:49 pm	#55
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis That sounds entirely feasible given that is was only after pulling the chassis for cleaning that it wouldn't even try to turn on anymore. I also measured the HT while it was on and it was fluctuating between 136 and 138v. Possibly as if there's a fracture it's only just making connection so whilenit looks like a deflection issue it could well be shutting down and powering up rapidly.

28th Apr 2019, 7:34 pm	#56
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,931	Re: Sony KV-2912U - won't turn on - AE-1A chassis Are is there an HT pot?(Intermittent) __________________ G8JET BVWS Archivist and Member V.M.A.R.S

28th Apr 2019, 8:41 pm	#57
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-2912U - won't turn on - AE-1A chassis There is but I've not been near it, worth checking out though

29th Apr 2019, 8:34 pm	#58
davyrocket2 Pentode Join Date: Apr 2011 Location: Westgate On Sea, Kent, UK. Posts: 246	Re: Sony KV-E2912U - won't turn on - AE-1A chassis I suggest having a very careful look around the area you placed the probe and look at each contact and find the other end to see if it has continuity there could be crack or a break that is too small too be visible

7th May 2019, 7:17 am	#59
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Re: Sony KV-E2912U - won't turn on - AE-1A chassis Continuity from Q607 to the end of those traces seems fine, no cracks in traces to my eye and now the TV stays on most of the time. After 20 minutes or so it will shut down but then power right back up for another 20 minutes or so. It's all very random and I do suspect there is a cracked trace but where it is I don't know. I'll come back to this thread if I have any updates. One thing I will say is this thing runs hot, it's no wonder there's so many heat related issues on these sets. I'm gonna install a silent fan in the upper case to extract some of the heat I think, maybe give it a bit more lifespan.

13th Nov 2019, 9:11 am	#60
Retrorepair Pentode Join Date: Apr 2019 Location: Denbigh, Wales Posts: 150	Sony KV-E2912U AE-1A Chassis - Part 2 Hey guys, I'm back with more issues with this set! So I finally got it to work reliably by reflowing all the daughter boards and it was fine for months but now I've a new issue. The set turns on fine and the neck glows happily but no image on screen, not even the OSD. If I leave it half hour it will finally show an image and stay that way until I turn it off but when I do, same thing. If I tweak the V size pot I can see the top raster so it is on but it seems the blanking isn't letting the image show. Does anyone know how I can disable this so I can see what's going on when I start it up? I'm guessing it's not a stable raster?