Hi Tony, Thanks for the information, that is all very useful! I think I will open up my VT420 which is working nicely to compare the glow in the base followed by checking the voltages, as you describe.
Thanks again! Aaron. Tony Duell writes: > On Fri, Apr 28, 2017 at 4:38 PM, Aaron Jackson via cctalk > <cctalk@classiccmp.org> wrote: >> Yes we checked for the glow. It's very dim but it is there. I will bring > > What do you mean by 'very dim'? It should be a distinct orange glow, > best seen looking > up the base of the CRT. > > I normally start by checking the CRT pin voltages. There's nothing on > the pins of > a monochrome CRT that can't be measured with a normal multimeter. The sort of > voltages I would expect are : > > pin 2 -- cathode -- 70V-100V > pin 1 or pin 5 -- control grid (the 2 pins are linked inside the CRT) -- > perhaps > 10V-20V less than the cathode > > pin3,pin4 -- heater. One will be grounded (0V). The other will be around > 11V-12V > > pin6, pin7 -- anodes. I forget which is the first anode and which is the > second > (focus) anode, but expect a few hundred V -- say 400V-800V on each of them. > > The higher voltages (cathode, anodes) will come from the flyback transformer > in the horizontal output stage, so if they're all missing, suspect problems > there. If the heater voltage is low, suspect PSU problems. > > I assume you have the printset (I think I got it from bitsavers). The monitor > section circuit looks very standard to me. > > -tony