SONY KV-2647R No HV

[ThePlague]

Hello All

I’ve been using this Sony KV-2657R 30P Chassis for about 3 – 4 hours a day for the last couple months. It appears to have been a low hour set with a very strong image.

Initially, the set would turn on it with a high pitch whine that would go away in about 20 seconds. Then recently it started doing the 20 second whine followed by a whine about 10 minutes after power on that would last around a minute. No picture degradation that I could detect, just noise.

A few days ago, there was a loud pop but the set kept running and the picture was fine. Sounded like a capacitor blowing. I powered it off and inspected it for any obvious signs of damage but found nothing. I used the set for another day and there was again a loud pop and I lost HV.

I inspected the unit again, but found no obvious signs of failed components. I suspected that the HOT may have gone bad. Pulled the HOT and performed a diode check and it came back fine. I replaced it with a NOS HOT I had just in case. I then noticed that the 125V 1.6amp fuse had blown. I replaced the fuse and powered on the set. That is when smoke came from resistor R539 near the flyback and there were high voltages arcing coming from the H-STAT on the CRT itself. I powered down the unit and pulled R539 and also C532 as it had a direct connection to R539 on one side and ground on the other. C532 came back fine, no short and capacitance value within spec. I also inspected capacitors C530 and C566 before the HOT as they had ties to ground but they were fine.

I powered on the set again and received a flash from the neon lamp NL601 for high voltage protection, the 125V 1.6amp fuse did not blow. There is no HV voltage present. I am a bit stumped as to why R539 would be the one to burn up, but I am now suspecting that its possible the flyback went bad, which would partially explain the whining sounds for the past couple months. The flyback is captured in the circuit as T502.

I just wanted to check with everyone if they have had a similar failure and if my flyback conclusion is justified. Thankfully I can source NOS flybacks for this unit for about ~$20. Hopefully there was no permanent damage to the H-STAT.

[vol.2]

Can't solve your issue exactly, but I can tell you what I would try in terms of troubleshooting. And obviously, you are responsible for your own safety when working around potentially lethal voltages, I make no guarantees for you. I will say though, don't work on a powered device without an isolation transformer.

Did you check the CRT tube for shorts?

You have the schematic with voltages. Did you verify that all of the voltages are correct under test conditions? (probably with rainbow pattern)

How is B+?

Did you check the main voltage rails for shorts?

[Username1]

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Hi!

I would check Q505, & Q506 also. And Sony's are very strange animals, If you replace
a Horizontal Output transistor, it often has to be a Sony part of the exact number,
not a replacement number. So be careful there.... Also there is that diode
built into that Horiz. Output Transistor, so "Diode Test" might not be
the best for that one.... And it's a Sony.... Also 2 of your scans are
not that clear & hard to read and follow.... But good luck with
the Sony..... And Yes, check voltages When that neon light
comes on I bet something is turned off to prevent HV
start-up.... Sony..... Also the neon light might be
the reason your fuse did not blow 2nd time,
Sony.......


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