Sir Bashir Ahmed . . . . .
Observations . . . .
What we seem to have there is the battery maintenance system for telecons 48VDC line ringer supply . . . BUT . . .with there being less and less need
for such a supply with the majority of phones now using simplified and less power hungry ringing alarm alerts.
Or if being a miles long remoted system, it being a supply for repeater amps tapping off from.
By the looks of that custom marble floor . . . . monetary consideration is being of absolutely NO concern . . . . just buy all new units.
However, that Harmer Simmons company is now defunct and aparently left with back rent due and has released their internet site to a porn site.
MOREOVER . . . with 6+ other units covers shown being torn down and visible , a good "engineer" should be able to easily take a working unit and evaluate voltages around the power switch mode and regulator circuitry to see what has gone awry in the somewhat stupendous outputting of 72VDC vice the normal 48VDC.
For sure, you have some salvageable / cannibalizable spare working parts for evaluation, instead of having an unknown one of a kind unit.
Your one good photo of the supply PCB did do good enough to date the units at circa 2000' ish by its parts being used.
On what little does show on that photo, one can see the AC power coming in from the top right corner and passing down to be rectified . . hidden . . .
and having raw DC power stored in the right bottom cluster of 220@450V E-caps to then feed to the center bottom ferrite based power transformer with its external yellow kapton tape wrap. The all important POWER semis would be mounted on the bottom corners heat sink.
You can then see the massive width foil paths if the unfiltered 48DC supply busses coming up and into the gold colored ferrite based filter balun L202 and the DC then passes thru R-03-10-22-and 23 surge limiting resistor busses and on into the 4 respective filters to their left. The processed 48VDC then gets switched by the hefty mechanical relay above them.
(Like relays . . . switch heater and broiler elements current capacities on electric stoves and ovens )
48VDC at 40 amps is being one HEFTY power supply.
And even more impressive, after charging the hefty, back up battery bank associated with it.
Thats all I can see without better photos to ascertain the unseen portions of the PCB power devices and their amcillary drive IC .
73's de Edd . . . . .
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No time for a bath? . . . . Easy Peasy . . . . just wrap yourself in masking tape and remove the dirt by simply peeling it off.