On Sat, Apr 29, 2017 at 2:34 PM, Aaron Jackson <aa...@aaronsplace.co.uk> 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