Help with Sencore CR31a CRT Tester

[egrand]

Does anybody else have one of these? I picked one up over the summer and it seems to work on all the functions except setting the filament voltage. When I set it for a particular volt range it shows on the meter somewhere in that range, but when I try to adjust the variable knob it only changes it about .1 volt on either side. For instance, when I set it to 6.3 volts the meter shows 6.6 and I can only adjust it between 6.5 and 6.7. When I checked the actual voltage at the socket it is 7.5v and still only adjusts .1v. Similar results on all the other ranges.

I'm thinking testing a CRT at that much higher voltage will throw off the other tests. I also think it should have a wider range of adjustment. I've replaced all the electrolytics and tested the resistors. The only resistor I replaced was the 15K 1W that was reading 16.6.

Could the transformer be bad or the diodes? I'd sure like to use this as it has 21 different adapters and a HV probe. I got a B&K 470 at the same time, but it doesn't have all the adapters for B&W. I bit the bullet and ordered the stuff to make my own universal adapter for the B&K, but I'd still like to get the Sencore going since I've got it.