Sony Trinitron KV-13FM12 brightness issue
 

This set has a very good picture except for the problem that image brightness flickers. If turn the tv on with no signal or a signal you can see the brightness of the raster flicker. It reminds me of watching an 8mm movie on an old projector but worse. Also the on screen menu doesn't flicker. My first thought it might have a bad cap as it does get little bit better once it has been on for a couple of minutes. I did test them but couldn't find any that had bad ESR.

:no: well that ended poorly as big dummy here forgot to plug the yoke back in when he went to test it. As you can expect that didn't do TV any good. I did plug back in the yoke but the damage has already been done.This set is a very very low hour and that's a shame that I did that I killed the set.

Are you sure the unplugged yoke fried something? I thought just about all TVs with a yoke plug had protection for running with the yoke unplugged? (Two pins on the plug connected together as a jumper, that removed power from the horizontal drive circuit when the yoke isn't plugged in) :scratch2:

Yes, they're *supposed* to, but in reality, some yoke plugs were simple 4 wire affairs with no interlock loop..

Without an interlock, an unplugged yoke can damage the horizontal output. This TV is "recent" enough where a shorted horiz output shouldn't damage the regulator...

John

Yoke connector was only a 4 pin with no interlock. The set came on and buzzed really load. I emideitely unplugged the set and then noticed that the yoke was unplugged. I hooked up the yoke and plugged the set back in. The set then emditly powered up and then TV just buzzed. I once again unplugged the set. I am surprised the microcontroller didn't shut the set down as it is from 2002.

The uPc wouldn't have much effect on these TVs. Most of the shutdowns are done in the circuits themselves.

For what it's worth, even pros leave plugs unconnected by accident. I remember leaving a CRT ground lead that would be connected to the CRT aquadag ended up draped over the chassis board when I was delivering the repaired board back to the customer's house (35" Zenith console). When the TV came on, the wayward ground lead spit HV onto the main board. It took out the jungle, comb filter, and micro in a split second.

Get an ohmmeter and check the horizontal output Collector to ground and look for a dead short - odds are the transistor failed when the yoke got unplugged. The buzzing however is odd. Normally, a well designed power supply will simply shut down on overcurrent if the output shorts.

Is there a schematic on-line?


John

Thank You John, I appreciate your response :thmbsp: