Quote:
Originally Posted by CRTs
Thanks everyone for the suggestions, I reached out to those two vendors but did not have any luck.
It's been suggested that there was never a cross for this part, and once NOS from the OEM was exhausted, thats it.
Feeling like a needle in a haystack situation now.
We're 95% confident the flyback is bad at this point. Per the retired tech who's been excellent at guiding and assisting me with this repair -
Once the sweep circuit is started we have decent amplitude of waveform going to the base of the horizontal output transistor. The transistor is working because there is a greatly amplified waveform at the collector; not enough, but very much more than the base. Also – the 220vdc source is flyback derived, but the waveform at that diode is only around 100v p-p. It is a single diode rectifier circuit (half wave) so we need to see around 200 vpp coming off the FBT to make 220DC.
Another also – the HV is produced by the winding of the flyback rectified by 4 internal diodes, per the Sams. Using the diode check function of my Fluke 73, I cannot measure any conduction regardless of what direction the probes are attached; very probable open HV winding inside the FBT.
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Is very difficult to measure these diodes with DMM or suchlike, due to large forward drop of each one. Better is to make a simple gig using a >20V PSU and a series current limiting resistor, and then measuring the resulting voltage in the flyback.
About Vpp of waveform, yes, even being very asymetrical in this case (H sweep), is needed to have sufficient Vpp to make work, and this directly reflects in the Vdc measured (if rectified is lower, for sure some issue is there).