On Monday, July 21, 2014 2:02:15 AM UTC+2, wrote:

Page 70 of the PDF shjows what is supposed to be feeding that, and it ain't good news. If you don't find a bad connection, you need a power trandformer. that is probably pure unobtainium.

Hi Jurb,

thanks for the info. I have the service manual, but even with that at hand I'm stumped (alas, no EE degree). As Mark pointed out, it *seems* easy enough.

There is continuity from the filament pins all the way to the PSU, so it's definitely not a bad connection. There's an 82ohm resistor between each 4VAC supply and the -30VDC centre tap which check out fine. There's also an electrolytic cap and a 4.7V zener diode in parallel in the -30VDC supply; they also check out fine. There's nothing else in that circuit on the display board, so I can't think of anything else that could fail there.

The circuit is basically the same as fig. 17 in Noritake's Guide to Fundamental VFD Operation (http://www.noritake-elec.com/vfd_ope...html#5VFDBias), only the whole thing is biased to -30VDC.

BTW, 6-8 volts is WAY to much vor that. They call for 4 VAC, you go to 8 DC and the thing is superheated. Hopefully it will be alright. That hting is even more unobtainable than the transformer.

The filaments don't begin to glow until about 5VDC. at 8VDC I'd say the display is bright enough to be readable through the plastic cover.

I assume these things do alter their resistance with age, right?

If it tunrs out to ne the trandformer, stop back for some - umm - engineering tips. I'm sure Digikey has a dandy off the shelf solution but it can probably be done cheaper.

Well, the xformer does churn out the 4VAC unloaded BUT I can't measure any continuity in the secondary, which is unsettling. Am I getting some spurious induction from the other windings?

Um, what was that about engineering tips again? :^)

Thanks & best regards,

--Roland