Yes indeed the good news is that the monitor suspected of having a power supply fault is working but with a ‘no fault found’ solution.
Four of these large CRT monitors are used in the LCP; they are Mitsubishi Electric model C3920 for display of 682 x 512 pixels.
Here are the four displays with the simulator running.
They require an RGB input with composite syncs superimposed on the green video channel. This shows the details of the non-standard video.
Pete H was doing the work in his home workshop where it took a while to set up a test rig with CHARGE cards etc to be able to drive the monitor with the non-standard RGB video used in the LCP system.
This set-up provides a test card from firmware in the CHARGE system to supply suitable signals for fault finding.
CHARGE (that is Compact High-resolution Advanced Raster Graphics Equipment) was devised and developed by Ferranti design engineer Peter Don-Duncan specifically for the Argus 700. There were few applications of the product and Bloodhound is believed to be the sole remaining user.
Inspection had already shown that there was no visible indication of a heat-damaged component and when first switched on there was nothing on the screen as per the symptom in the LCP. After checking the 6.3V supply voltage for the tube heater voltage Pete noticed the EHT was OK …. no not because he got a belt from the supply of25kV DC but because he felt the static charge on the CRT face!
There was still nothing on the screen though so Pete proceeded to check some details when around he glanced at the screen and noticed that the test signal was displayed. So what was the fault … poor continuity on connector or an obscure dry joint!
The monitor white balance needs setting up and I’ll do this during the week.
So, what about the smell of burning experienced in the LCP ? Thankfully it wasn’t the Flyback transformer in the monitor which is a great relief, so a suspect is the usual problem that initiates a nasty smell namely a RIFA filter capacitor going in a Farnell power supply. I’m sure we have replaced all the filter capacitors in the computer rack PS’s but when we have time those in the display console and in the rack (is it S rack?)
could do with a check. A filter capacitor going U/S does not stop a PS from working.
This is a great relief as every time a monitor fails it starts me thinking about how we can replace the Mitsubishi monitors!!!!