Work Day 29th May 2021

I picked up on the monitor that that we struggled get the vertical hold stable on last week. It was impossible to adjust the vertical hold with the monitor in situ so the very heavy monitor has been taken off its runners and sits on an old pallet ‘table’ (see below) so I can now get at the variable resistors.

CRU1 and CRU2 can also be seen in the photo, these have now been refitted and the side of the display console is back on. Unfortunately there was still no success in adjusting the vertical hold so does the problem lie with the monitor or its CHARGE channel? (CHARGE being the Ferranti-designed video system – Compact High-Resolution Advanced Raster Graphics Equipment).

I replaced the monitor with our spare which gave a perfect display until it started to show additional horizontal lines.

It was now that other faults with the displays appeared. The Engagement Controller’s display became a white square and the Jamming Assessment display lost it’s vertical hold but I suspect that is the monitor.

Note: The monitors are mounted on their side so what appears to be a loss of horizontal sync is actually vertical sync.

Last week Pete M said ‘first thing to do next week is check the +/- 5V at the CHARGE box’. I actually used a card extender and measured the +5V on a TTL device on a CHARGE card, it was 4.5V! Answer, crank up the +5 power supply but that didn’t make any difference and the +5V power supply is rated at 120 Amps! Is this a problem with the heavy loading of the CHARGE +5V in the LCP? A couple of monitors also need setting up or fixing, e.g. the instructors monitor has low brilliance and looked to have lost a colour (that problem comes and goes) and one CHARGE channel didn’t look to be working – could be the low voltage. The plan now is to give the monitors a refurbish and set up and also check out the suspect CHARGE channel and the spare CHARGE card set.

Here are the CHARGE cards used. There are four sets of cards (one for each display) with each set comprising two Pixel Stores and a Controller. As can be seen these are very complex cards that do not lend themselves to easy fault-finding and repair.

CHARGE Pixel Store
CHARGE PIXEL STORE

CHARGE Controller
CHARGE CONTROLLER

A couple of weeks back all the digital input and output cards were checked for bad AVX decoupling capacitors that were acting as low value resisters and loading their +5V supply (In this case it was preventing the simulator from booting). The CHARGE cards use the same AVX capacitors so these will now be checked as it could explain the power supply loading. Eliminating such ‘known’ problems and refurbishing connectors etc. on PCB’s and monitors in the LCP/simulator will, hopefully, improve reliability.

Last week the LCP roof struts were refitted and this week R clips were fitted to the securing pins as opposed to split pins. The R pins couldn’t be found last week as they had been put somewhere safe!

Pete H

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