Hi I trying to fix Sony KV-27FS12 27' TV.Front LED blinking 4 times.I found short horizontal output transistor D2578.After replaced and try to turn on TV the transistor blow out again after it start working for few seconds.There is no bad solder connections on the board.I suspect bad flyback.Any suggestions?Thanks
A scope and basic troubleshooting...
Leonard
The light bulb trick would have saved the HOT...they don't short for no reason...this thing, if memory serves, requires a multiple-step troubleshooting procedure that I don't recall, the ability to vary line AC input, etc...if you can't find the correct procedure, and don't have the gear, take it to a shop that can repair it.
Tom
First thing I'd check are electrolytic capacitors, Sony sets that are blowing parts can be a real pain to fix, they're good units but very touchy in some respects and have to be fixed just right.
I checked the caps which is involve in B+ line.All good.The TV start doing HV but for few seconds then Horizontal output transistor blow out and TV shut down to safe mode.I checked HV by HV meter connected to anode.Any other suggestions.
PS TO TOM I'm a shop working in this business for 15 years.Fixed previous models of Sony for 5 minutes especially when 2 blowed out transistor in power supply and in chain reaction of blowed HO transistor.I never had the problem like this with Sony that's why asking people who got similar problem before to safe some time on troubleshooting.
Check the pincushion diodes and the related passive components in the output stage.
If you can, drive test and ring test the flyback. Also, look at the collector waveform as you start it up and if it doesn't go directly to a clean pulse with no ringing, you likely have a bad flyback.
These sets have had bad flybacks and problems in the pin circuits that will blow outputs.
Le>>
Replace any electrolytics in the horizontal drive circuit. Did the HOT get hot before it failed? If it did, I would suspect a horizontal drive problem.
It could be a bad flyback, but the bad Sony flybacks I've seen always caused instant HOT failure. Andy Cuffe
snipped-for-privacy@psu.edu
I have seen quite a few that do not blow the output. Just changed one in a KV36FV16 that would shut down on trying to start. Rings bad out of circuit, had ringing on the collector pulse in circuit, and drive tests bad. I have seen some Sony FBTs that ring good have a clean pulse and only test bad on the drive tests.
Leonard
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