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Vertical problems on PTK195

Occassionally I have PTK195 lightbox come in with coolant slop on the front most PCB where vertical circuit & micro are. Usually a wash and check of components fixes these after several rounds.

Except this one is resisting me. BTW this particular is P56830xxyyy

Every components are checked, cleaned if required and replaced: diode, caps, and 8 pin SIP reistor pack and vertical IC.

Every time the vertical is turned on or replaced, The 26V side vertical amp stage dies slowly in several seconds but the ground side of vertical amp stage is working, giving noisy 3" band of raster in middle. No overheating or blowing craters.

RCA uses TDA8172 IC between 26V supply and ground with 15V feeding through IC's output via vertical yoke winding. Voltages are there and

15V starts good then unloads to around floating 22V as deflection slowly collapses. So waveforms looks like a flat waveform with small pips for retrace and a ramp sloping down from 15V mid-point to ground.

BTW, 26V is there at vertical IC, no noise either.

Cheers, Wizard

Reply to
Jason D.
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Missed some spillage or corrosion on the board there Jason. Cleaning and restoring these after the glycol seeps into the boards can be a real challenge. I'll bet some of the glue under smd components have become contiminated as a result. Going to take a bit more inspection and cleaning to restore the beastie.

Reply to
Papa_J

Sometimes you have to take out the Micro / EPROM and chipper socket just to be 100 percent sure. Isn't that vertical IC feed with dual V+ ,one from the fly. Diode and small resistor I got caught once now I change em when I see em. Dont even check them just replace them.

kip

Reply to
kip

26V and 13V comes from fly via two diodes. Does this help?

Vertical only get one feed, 26V, the 13V is fed through yoke winding to the vertical IC output as midpoint between 26V and ground. Been this way since CTC17x even eariler through ATC113.

To others, The only one SMD is capacitor for vertical circuit itself, already replaced with another and through cleaning. The other SMD items is only for feedback pulses back to the chassis.

I'm very certain that coolant did not leak onto component side because the holes were shut with original solder and did careful check just in case. Previous one had few open holes and got some on solder side.

Washing goes like this: HOT tap water (nearly 70C) TSP then rinse then hot water & oxiclean, rinse throughly, then alochol drenching for assisting drying. Then dried carefully with heat gun. Yes did both sides. Done two before with success. That's for only 4" band along front area where coolant tend to hit anywhere; audio amp, micro, pincushion and vertical circuits.

Cheers, Wizard

Reply to
Jason D.

I was told by the RCA rep to use an ammonia based cleaner like Windex for the first wash as ammonia breaks up the glycol coolant. Have done many that way, windex, followed by water/tsp, then distilled water rinse and alcohol to aid drying. I reccomend some compressed air, make sure to blow out from under connectors /components. If the fluid has been on there a while be sure to check for corrosion underneath components, had that problem before on a Samsung with fluid problems. Cleaned it and the HOT kept failing, the drive transformer had conductive goo underneath it.

Jammy

Reply to
ampdoc

Been there many times I have seen coolant corrode components leads in two. Got this fixed too. This latest 195 got me really stumped!!

Cheers, Wizard

Reply to
Jason D.

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