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Started work on the HV issues on the two Type 547's. Experimenting to see if I can get the HV to stay up without resorting to removing the HV transformer and figuring out a way to get it rewound.
Schematic of HV circuit.
Making sure the scope still has good power and trace. It does.
All the covers removed exposing the five 5642 HV rectifiers. My initial plan was to just change the HV disc capacitors first. But I discovered that the capacitors are underneath that plastic assembly which would require removal. Quick change in plans and decided to just change the HV rectifiers first and check results. Installing SS rectifiers eliminates the filaments which in turn lightens the load on the HV transformer. So in theory it should run with less load on the HV Oscillator which in turn may prevent a shutdown. That's the theory.
The five SS rectifiers installed. The 5642 HV rectifiers will be kept as spare stock. There's nothing wrong with them.
Power up and no arcs or sparking. Set the HV test point at the CRT cathode to the spec'ed -1850V.
Perfect trace. Sharp and plenty of brightness. Everything was great, at least for a while. After about 20 minutes noticed the trace was growing both vertically and horizontally. So much so that a 0.5V p-p was displaying in excess of 0.6V p-p. I had already buttoned everything back up so I'm going to have to remove all the covers again and monitor some voltages. That's going to be follow on and I'll post results.
In other news. The 7B92 500MHz timebase plug-in showed up. It was missing one of the side covers but I have some spares from parts units. Other than that it's in very good shape. Some pictures of the internals. This plug-in is packed tight. At least 3 layers deep. And surprisingly heavy.
Well guess what? Seller sold it as fully functional. It doesn't work. No trigger, no sweep, no trace. I contacted the seller. I'm getting a full refund including shipping and he stated to keep the plug-in. So I'll put it in queue for future repair.