Work Day 19th December 2020

The 24V 10A PS (Power Supply) in L Rack that failed two weeks ago is serviceable again. I confirmed that there was no output at home and did my usual checks and removed all the Tantalum capacitors on the controller board; there are four, two off 22uF 16V and two off 22uF 25V. Checked all four and both 22UF ts were dead. The ESR is usually around 0.5, not 0.12 as these were (see below); they were changed and the PS burst back in to life.

I still went ahead and changed all the RIFA capacitors as several were showing crack in their casing. A time consuming job but it has to be done while on the unit is on the bench.

Also, the G6 40A PS that went up in smoke has been repaired by changing all the RIFAs for Metallized Polypropylene X2s and it tested OK once more.

So the plan for last saturday was to refit the power supplies and change the FT81 monitor and test out the Simulator.

It was cold and damp as always during the winter months in the hangar and all work is still concentrated on the LCP.

The repaired power supplies are back in operation.

The FT81 had lost its Y Hold and was found to be a simple matter of adjustment. This is now fully serviceable as can be seen on accompanying photo displaying a test screen of H’s.

The issue now is that equipment works in a dry and warm environment, put it in the LCP in its cold and damp environment where it needs resetting or at worst goes U/S.

Attempts to get the LCP simulator up and running after the cabin repaint have taken a step forward and a step back again which is frustrating. Power supplies keep failing, mainly due to the RIFA X2 capacitors not being able to handle the damp conditions. If it’s not the X2 capacitors it’s the small bead tant capacitors that are not keen on the damp. An example of these problems is when a power supply was transferred to the LCP from the test set up in 2nd Line (spare room at home) it has gone U/S in a week with what looks like a Tant capacitor failing.

So, it was time to start switching on again. First task, connect the SCSI disk emulator to SCSI cable and plug in its 5V power supply, the one I used last week as it was left in the LCP. This time no 5V, the PS was dead!!! No great problem as I can plug the SCSI disk emulator in to the disk system power supply in the computer rack. Second task, check the Argus powers up before switching on the I/O rack and display console. Last week the Argus came up OK before a power supply failure but this week there were no LEDs on the front of the GX processor, it looked dead! Not going too well so far but then I looked at the replacement FT81 and that had now lost its Y Hold and this was the monitor I soak tested for hours at home! (Exclamation marks reflect my frustration). Not the end of the world though as I can switch off the Argus and just power on the I/O rack and display console, at least it will get power on after all this time and I’ll see if the monitors display the CHARGE firmware info. Switched on and LEDs on the I/O cards came on so looking good but only two monitors are showing the CHARGE firmware display, Instructors and Tech Sup. A quick look at the CHARGE cards show two sets active but the other two sets look dead, no green LED. This could simply be a power switch  on the back of the CHARGE chassis but at this stage I couldn’t be bothered to take the rack cover off to check! Time was getting on and at that point yet another power supply went up in smoke in the computer rack as another RIFA capacitor failed. Definitely time to go home.

I haven’t returned any spares to the LCP after the repaint and I’m now taking a different approach to faults. Obviously the cold and damp in the hangar is playing havoc with the kit, mainly the power supplies and the Argus cards with their interconnections and backplane connectors. Leaving spares in the LCP is not good, especially over the winter months.

We are dealing with kit that is around 35 years old and getting directly to the point there is no merit in running, or trying to run, the LCP during the winter months at least while it is in it is current environment. It may be cold and damp but we are fortunate to have both the LCP and T86 under cover while restoration is ongoing. Another factor is that we have not been able to keep the LCP ‘warmed through’ for the past year when the various lockdowns prevented access.

As time allows I’ll press on at home, checking the Argus cards, fixing both the SCSI emulator PS and also the latest PS from the computer rack that failed today. I won’t be at Cosford next Saturday but will find a day to return before the New Year but even that will depend on lock down status.

To all our readers best wishes for your Christmas and we have the new year to look forward to, stay safe and well.

Pete Harry, Mike Strange and the BMPG Team.