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Put in a few hours after work and got our friend Pandora's Autex 1600 fully working. This unit is the smaller cousin of the big Message Exchange Switch that we had at HQ and would have been installed in Council bunkers up and down the UK. They would have been connected to a couple of printers and terminals and were used to send messages around to other Council bunkers, the ROC and RGHQs.
When we got it the unit didn't power on, there was a tripped circuit breaker at the rear of the unit. All the voltages from the power supply were alright, the big capacitor on the backplane was changed and all the tantalum capacitors on the boards were changed because they often become short circuited with age. It's quite likely that the circuit breaker tripped when a tantalum capacitor went short circuit and caused too much current to be drawn from the power supply. Three of the tants tested as faulty once they were removed. After all that the unit switched on, but didn't initialise properly and just lit up all its LEDs.
A bit of detective work lead to finding that of all the board sockets on the backplane, only one of them had contacts for both sides of the PCBs and also that only one PCB had contacts on both sides of the board. The double sided board wasn't in the double sided socket and was duly swapped over. We checked this against a photo of a working unit and Dundee and verified it was correct.
After that the unit still didn't power on and so we started looking at the battery backup for power and found the 6V lead acid battery was only sitting at 3V. It was so low that a 6V battery charger wasn't actually believing anything was connected and wasn't charging it and so we gave it a quick blast on a 12V car battery charger in low voltage recovery mode and that did the trick in just a few minutes. Once the battery was back at 6V the Autex fired right up, the clock LED began to flash and we knew we were in business!
The backup battery is to keep the RAM chips powered on to preserve their contents during power cuts. Rather than keep the whole unit running there is a ribbon cable which just keeps the RAM powered up. If the battery is dead then the RAM doesn't get powered so the unit doesn't initialise. It's an interesting design, but means a broken battery will leave you high and dry.
To finish off the repairs the broken mains cable gland was replaced. It's great to see another of these units running and in a few weeks we will get the two 1600s from our bunker repaired and running too! ...
Phew, that’s done for today, a huge difference. We’ll have to repeat it next week with the mower to sort out all the tufts and lying down bits.
We haven’t been able to run tours this year because of Covid19 and we have still had outlays such as a new brushcutter and so on. We realise that times are hard all over, but if you can spare us a few pounds to
keep us in petrol and strimmer line it would be very much appreciated. Please see the Donate button on this post. ...