Sony KV-1320UB MK1 Power on/Screen fault - UK Vintage Radio Repair and Restoration Discussion Forum

JoeDoyle · 26th May 2025, 6:09 pm

Hi all

When powering on this set snow appears with no signal as expected but then an uncontrollably bright screen with lines going across it appears, then the snow reappears 20 seconds or so later and it behaves normally. What could possibly be causing this odd fault? Also, if I power this set off when this fault starts and turn it back on soon after it's OK too. Please can someone point me in the right direction? Many thanks, Joe

John123 · 27th May 2025, 1:42 pm

Hello Joe,

The symptoms you describe sound like typical bad capacitor behaviour. Check the flyback boost cap and caps surrounding the line-output transformer, RGB drives, CRT neck board, etc. Also check for dry solder joints especially in high-heat areas of the PCB.

Given the age of the set, it may be pertinent to re-flow the solder to all pins of the line-output transformer with quality leaded solder. Always good practice with most sets, even relatively modern ones.

As always, the necessary safety precautions when working with a live TV chassis. We don't know your skill level so if you don't feel confident, perhaps try a request in the 'Repair and Restoration Services Wanted' section of the forum.

JoeDoyle · 31st May 2025, 10:15 am

Thanks John,

I will do as you suggested, there’s a cluster of 160v capacitors next to the line-output transformer. I do have a capacitor tester, so I’ll disconnect each one and test in turn. I will resolder all the pins of the LOPT too. I’ll report back on how I get on.

JoeDoyle · 22nd Jun 2025, 5:51 pm

This is a bit of a late response, but I found the fault. R901 which forms part of the instant on circuit with the tube heaters, was removed to try and illuminate another fault but it didn’t work and I left it out anyway because I didn’t like the idea of having tube heaters on when plugged in. I reinstalled R901 and the fault ceased.

Maarten · 22nd Jun 2025, 9:32 pm

Unless you start up the set while the cathodes are still cold, I assume?

26th May 2025, 6:09 pm	#1
JoeDoyle Diode Join Date: May 2025 Location: Bristol, North Somerset, UK. Posts: 9	Sony KV-1320UB MK1 Power on/Screen fault Hi all When powering on this set snow appears with no signal as expected but then an uncontrollably bright screen with lines going across it appears, then the snow reappears 20 seconds or so later and it behaves normally. What could possibly be causing this odd fault? Also, if I power this set off when this fault starts and turn it back on soon after it's OK too. Please can someone point me in the right direction? Many thanks, Joe Attached Thumbnails

27th May 2025, 1:42 pm	#2
John123 Heptode Join Date: Jan 2007 Location: Luton, Bedfordshire, UK. Posts: 929	Re: Sony KV-1320UB MK1 Power on/Screen fault Hello Joe, The symptoms you describe sound like typical bad capacitor behaviour. Check the flyback boost cap and caps surrounding the line-output transformer, RGB drives, CRT neck board, etc. Also check for dry solder joints especially in high-heat areas of the PCB. Given the age of the set, it may be pertinent to re-flow the solder to all pins of the line-output transformer with quality leaded solder. Always good practice with most sets, even relatively modern ones. As always, the necessary safety precautions when working with a live TV chassis. We don't know your skill level so if you don't feel confident, perhaps try a request in the 'Repair and Restoration Services Wanted' section of the forum. __________________ Regards, John

31st May 2025, 10:15 am	#3
JoeDoyle Diode Join Date: May 2025 Location: Bristol, North Somerset, UK. Posts: 9	Re: Sony KV-1320UB MK1 Power on/Screen fault Thanks John, I will do as you suggested, there’s a cluster of 160v capacitors next to the line-output transformer. I do have a capacitor tester, so I’ll disconnect each one and test in turn. I will resolder all the pins of the LOPT too. I’ll report back on how I get on.

22nd Jun 2025, 5:51 pm	#4
JoeDoyle Diode Join Date: May 2025 Location: Bristol, North Somerset, UK. Posts: 9	Re: Sony KV-1320UB MK1 Power on/Screen fault This is a bit of a late response, but I found the fault. R901 which forms part of the instant on circuit with the tube heaters, was removed to try and illuminate another fault but it didn’t work and I left it out anyway because I didn’t like the idea of having tube heaters on when plugged in. I reinstalled R901 and the fault ceased.

22nd Jun 2025, 9:32 pm	#5
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,719	Re: Sony KV-1320UB MK1 Power on/Screen fault Unless you start up the set while the cathodes are still cold, I assume?