Anyone know of any "typical" failures on a Sony Trinitron KV-27S10 (manufactured 9/94) that would make it dead as a door stop? I had bought the set for my parents, and had worked without a hitch for years. Just recently they were watching it and the picture just disappeared. I recently picked up the set from them (bought them a new one) and have done a cursory external review of it. It's dead!
When plugged into the wall, sometimes can see a tiny arc at the plug when put in the socket. No humming, no noise, no lights, nothing. Tried the power button. Tried the remote. Again nothing.
Any suggestions as to what might be wrong or what to check? I am pretty handy with electronic stuff, but mostly in the digital domain.
There are a lot of possibilities and causes for the set to be dead.
You will need to do some basic troubleshooting and voltage measurements for specific help. A good place to start could be the user switches, check for 5V dc to see if the standby power supply is running, then you can scope the system control ic to see if it is running.
Make sure you are fully aware of the safety required when working in the tv set with it plugged in. I strongly recommend you have the tv plugged into an isolation tranformer as it increases the safety margin for both you and your test equipment.
If you do not know the difference between the tv sets hot and cold grounds, do not attempt to do anything inside the tv until you find out and the related implications of both.
Typical failure: 2SC4927 shorted horizontal output, bad connections @ the horizontal drive transformer, shorted Q601, & 602 2SC4834 PWM switching regulators, open .1 ohm fusible resistor R607, VDR 601 bad 1-807-288-11, & "possibly" bad VDR 602, & 603, but these are usually ok.
I keep seeing this recommendation for changing the VDRs. While there may be some value in changing them due to damage in the metal oxide from repeated conduction events, when the HOT fails and takes out the power supply, the VDRs are not likely to be a problem. VDRs are protection or dumping devices. If they check open with a DMM they are not likely to be a problem in the PS. They can be tested for clamping voltage, though if they are failing, they fail by leaking rather than not clamping at near the rated voltage. A handy way to test them is with the h-pulse drive on a sencore tester and a scope.
It is more important to use the correct parts, ie higher rank 2sc4834 and to verify the duty cycle of these. I use P rank versions, that we get very inexpensively from ACME Enterprises in Orlando and match them. Virtually all units that fail this way are fixed completely with just the HOT, Q601,Q602, R607, and resoldering the components in the base circuit.
When the PS fails on its own or due to surge damage, it is important to check all of the components in the primary, particularly the poly caps. Of course, the VDRs are suspect in these cases. When the PS fails due to loading such as a shorted HOT it is rare to see problems other than the parts listd above.
Also, the 2SC4927 can be replaced with several other transistors that will run cooler and may be more reliable. We have had success with the 2SD1881 but others will work as well.
"When the PS fails on its own or due to surge damage, it is important to check all of the components in the primary, particularly the poly caps. "
... check for blown fuse(s) in the power supply section,due to voltage surge or lightning strike. This event is quite probable and is simple to detect and repair. .... If not familiar with safety procedures, always unplug the power cord first.
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