Greetings to the group:
I had a working RM-561 until the display died. It had a brief time of intensity going bright to dark intermittently. One day I turned it on, and I had no display. Got into to it and found my -3300V down to -200V, When I disconnected the main power transformer filament winding to the CRT, my -3300V came up to -3600V, so it would appear that my main power transformer CRT filament winding insulation has broken down. (I never checked the actual 6.3V due to the HV on it).
The original power transformer is part number 120-280. I have a pull from another 561 that appears to be a later revision (it has the silicon diodes) and it's part number is 120-280-00. From what I can see, it appears that TEK beefed up the filament windings with a heavier insulation (almost rubbery compared to just enameled wire). Almost like they knew these would go bad.
Before I get busy swapping it out (looks like a big job), I have some questions to the brain trust of Tekscopes:
1) can anyone confirm for me that the -00 power xfmr is in fact a revision with regard to the CRT filament winding (with the HV on it) ?2) Is there any way to rig up an alternate 6.3V CRT filament supply? Of course, the regular 6.3V filament xfmr won't be insulated to 3.5kV? Has anyone done anything like that? (Back in my TV repair days, we would eliminate a shorted CRT by winding a separate filament winding on the flyback).3) Is there a specific reason to elevate the filament to -3300V? What if I just powered it with a regular filament xfmr isolated from the -3300V?? The Cathode of the CRT comes off on a separate pin and does not show an internal connection to the filament on the CRT. 4) Will Tektronix warranty my defective transformer with the so-called lifetime warranty? :)
Regards, Ryan ScottN7QJ
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