It was on with the painting of the wheel arches and other bits and pieces under the chassis; a time consuming process of preparing, corrosion treatment, priming and top coat
Mitsubishi C-3920 Display
One of the display monitors developed a fault which gave the appearance of a free running display sync. Initial investigation soon exposed the problem, see the two accompanying oscilloscope screen shots of the H-Sync and V-Sync at the output of the video circuit (inputs to the deflection circuit). The first shows the defective monitor and the second a working one
Fortunately we do have the circuit diagrams for the monitor so it was down to some old fashioned fault finding.
The horizontal sync is stripped from the green video input from CHARGE, all RGB video channels were being processed correctly by the monitor so everything pointed to the creation of the vertical sync which is created by a few TTL 74 series devices including NAND gates and a couple of mono stable multivibrators with timing set by capacitor and resistor combinations. The fault was eventually fixed once the capacitors and TTL devices were changed, there was no single point of failure. Components were changed that improved the vertical sync but stability wasn’t achieved until all the TTL and capacitors in the vertical sync circuit were replaced. The display of the now serviceable and stable monitor is shown in an accompanying photo. The now serviceable monitor shows the ‘firmware display’ created by CHARGE before a video input is received from the Argus 700.
One of the challenges with the Mitsubishi monitors is the setting up of the video and deflection PCB’s. Following this latest repair a new BMPG version of the set up instructions is being created for the simple reason that set up instructions in the manual don’t do what you expect, that is balance the RGB video with sufficient contrast etc.
Yet more time was spent on the radar chassis with the focus on surfaces that can be seen, wheel arches, the chiller boxes etc. The hidden chassis components can wait. The reason is that time will be needed over the coming weeks to get the T86 aerial assembly components installed, the In-Flight Reference aerial etc. I also intend to get the internal chrome handles and fittings for the T86 cabin re chromed in the near future. I need get to Dudley to organise that. No photos of the chassis this time, there’s only so much of a good thing you can dish out.
Away from Cosford
A start has been made on fixing one of the Mitsubishi C-3920 display monitors. The accompanying photo shows the faulty display which is only present when the video is connected. The photo shows the test rig for running the monitor in second line – a spare bedroom.
To fault find I use a USB PicoScope so it’s easy to capture images. The two attached are of the horizontal (top) and vertical (bottom) syncs from the video PCB to the deflection PCB. The vertical sync looking somewhat random.
We have the circuit diagrams for the monitor but we do not have a test schedule or examples of typical waveforms for a working monitor. To rectify this I have brought back a spare (working) monitor from Cosford and will create a test/reference document to use in future fault finding. It will also help with the current fault.
Nothing much to report on this week as the day was spent abrading and priming the patch that Pete M fitted last week to the back of the LCP box body and carrying out preparation and corrosion treatment on another T86 wheel arch.
An aside, can anyone recall seeing this radar map attached to one of the LCP drawer assemblies that are now at the Hack Green Cold War Bunker? We are trying to establish which LCP the units come from.
This is part of a mock-up of radar displays driven by the LCP sub-assemblies shown below