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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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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 |
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