Quote:
Originally Posted by TheSquirrel
... trying to determine the cause of the frame collapse and I've been looking in the area of the frame coils circuits, fusible resistors, electrolytic capacitors and the vertical control IC, IC301, a TDA1170s.
I've been looking at building a safe discharging method for the capacitors and CRT.
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Generally you are on the right track. For this sort of fault (Frame scan collapse) you don't need to worry about discharging power supply caps, or the CRT for that matter (as there is no need to take the crt's eht connector off or pull off its base socket). The power supply caps will self discharge due to leakage if you wait 20 minutes, likely there will be bleeder resistance anyway, but its really academic for this fault, because the tests you need to do, ideally, are done with the unit powered up anyway.
The common faults for zero frame deflection current in the yoke are failed power supply to your frame oscillator or frame output stage, all of that is in your TDA1170 IC (perhaps a fusible resistor powering it is open). The TDA1170 itself could have failed, they can run hot. Even if the power supply filter capacitor on the TDA1170's power input supply had failed unlikely it would stop the IC from working completely and there would be some frame deflection.
(The frame output stage is very much like its power audio output stage counterpart, its a linear amplifier primarily. The frame deflection output amplifier (in your IC) is designed to apply a trapezoidal shaped deflection voltage to the yoke, which produces a linearly increasing ramp of current with a rapid crt beam flyback, back to the start of vertical scan)
So to fix this fault the best move is to power the monitor with the brightness set to near zero (you don't wan't to burn a horizontal line into the screen) then test the power supply to the TDA 1170. If the supply is there, I would suspect the IC, or one of the components immediately associated with it. If its power supply feed has failed, find the reason why.
If you can't get the exact schematic for your particular monitor, just look up the data sheet for the TDA1170 instead, the circuit will be nearly identical to the example circuit there.
Here is a useful data sheet:
https://datasheetspdf.com/pdf-file/1.../SGS/TDA1170/1