This thing is f___ing haunted or something. Other person does not bevlelv my conclusion either, so I present it to you.
The ticket says "dead". I plug it in, with my handy scope probe near the SMPS transformer an it looks normal. The normal stuttering and then normal, well normal for that chassis. I pointed my remote into the crack between the lightbox and the top back of the cabinet. The set fired up !. I unplugged it, went to check caps in the SMPS, found 350V units in there, replaced them. OK , but not the right track.
When I went to fire it up again, it crackled and shut down. I was thinking coolant leak but I now pull the CRT leads from the HVB first. This is soon becoming an industry (axiom ?) standard with me. Due to the frequency or cracked CRTs and coolant leaks, it is worthy of checking into.
I have scoped the 143 and 15 volt lines during startup, and have already replaced both of their rectifiers. I scoped the main, and I know sometimes you can't see on the scope, so I clip leaded in a
470/200. No good.
Now in this set, standby B+ is only 138 volts. Caps have been changed. Both diodes as well. Also the 205064, and it now shuts down even disconnected from that.
I scoped the regulated B+ and it is not getting excessive, We know it's not a coolant leak because the CRTs are disconnected, and get me right on this, the lead to the focus block has been out as well. Everything has been checked independentely.
Checking the HV is a real bitch in this chassis, but I might just have to do it. Pin 5 of the fly is putting out 38V P-P and that is high. If you look at the shutdown detector it feeds you can see, and it's also almost as high to the actual filaments.
I am leaning toward a bad fly, but I relly don't want to order one unless I'm sure.
Could this condition be related to the totally FUBAR way they derive the 220 and that other source ? Could..................
I will let this post stand, it got me here. This is what seperates the Men from the boys.
I just figured it out, it it the fly, but a wierd thing, one connection is broke. Specifically the connection that grounds the main secondary for all the scan supplies. You see it is no longer grounded in the proper place, and somehow this double forward/reverse rectifying system they got is providing a ground. This means there is a leakage path also.
Not for sure, but that is a floating winding and funny things can happen to floating windings.
Mind you that everything else is normal off the fly. All scan derived sources are , well I checked most of them. It is just putting out a 38 volt pulse on pin 5 instead of like a 28 volt pulse. The pulse width is normal.
Has anyone seen this happen before ? and if so, is it the fly ?
Thanks for anything.
JURB