Seems to be working fine as a terminal hooked up to the TV which is good news. I am sure you are correct about me having made a measurement error there...
I'll take another look at the schematics. Thanks again, Aaron. > On Sat, Apr 29, 2017 at 2:34 PM, Aaron Jackson <[email protected]> > wrote: >> The heater and control pins appear to be giving sensible voltages. The >> logic of the board is fine, I can type on the terminals keyboard and I >> get the correct characters on the other end of the serial cable. The PSU >> is putting out 31v which seems fine? > > Err, the PSU has 3 voltage outputs, +5V, +12V, -12V. I am not sure where you > are measuring 31V between, but that doesn't sound 'fine' to me. > > On the other hand, if the +12V rail was 31V the CRT heater would be burnt > out. If the +5V was 31V then the logic ICs would be totally fried so it > wouldn't > respond to the keyboard. > > So I suspect a measurement error.... > > >> >> I'm used to discharging the tube before fixing things inside CRTs >> (usually I only attempt to fix simple things like a broken toggle >> switch), but I have not managed to get a spark off this monitor. The >> tube doesn't seem to get charged up at all. I've measured the >> capacitance of nearly all caps and they seem fine, diodes seem to be >> working fine. Does this mean it is most likely the flyback transformer? > > According to the schematic of the monitor section (p16 of the 17 page > .pdf file I have) there is a bleeder (discharging) resistor between the EHT > output and ground inside the flyback. This would discharge the CRT in > a few seconds I think. So you probably wouldn't be able to get a spark. > > I assume you don't have an EHT meter. > >> Are there any other bits I should be wary of and test properly? >> >> Thanks again for your help. Your voltage listing and advice in general >> has been very useful. > > Do you have a TV-rate video monitor with a composite video input? If > so, connect it to the BNC socket on the logic board. That's a video > output. If you get no video there, then you need to troubleshoot the > video logic first. > > -tony
