STx....Has the TX backplane, got any "Surface Mount" bits ? or are they, all "Though Hole" normal type bits?
Working from memory (because i couldnt take any pictures!) The backplane is segmented but it would be virtually impossible to change one segment because of the common coupling bar (transformer secondary) running top to bottom. There are also daughter boards on the backplane boards with tuning coils for each amplifier prior to the main coupling torroid. Its mainly edge connectors and co-axes terminating on the backplane, but labour intensive to change.
Also, can you get, to the Rear of the backplane PCB, through the back doors ?
Yes by removing some vented cover plates
Reading up on it, seems there are Four boards, each with 16 PA module sockets on, a total of 64 plug in modules. Yes something like that, amps sit side by 2 X 32 although a lot of the modules are not actually in use because its not running at 25 kW. There are also amps that run at lower powers called the binary amps which fill in the gaps between the high power amp steps. The amps are essentially on or off depending on the instantaneous power needed. There is a very complex looking board accessible from the front which decides how many amps are required at any given time. I hope that never goes wrong !
Each module has a Ribbon cable connector, well known for bad connections, with the IDC "Forks" not right home.
Yes this seems to be the problem and of course you cannot see the tracks when they pass under the ribbon connectors. This is where we think the problems lie.
As you say, quite a time consuming job, especially as the copper tube, that goes through all the Toroids, (as a secondary)
needs unbolt, to get one of the Four backplane PCB out.
Absolutely. its a major strip down.
Do the Plug in PA Modules, just have male PCB "fingers" that plug into female sockets on the mainboard?. Yes they slide in and out quite easily.
Can you see corrosion on the solder pins etc? have bits just bad tarnish, or rotted away?
The whole thing looks to be in poor shape, particularly where the cooling air passes over the boards. I think there are three air inlets each with a fan pushing air in.
You can just about see the backplane and daughter boards on the caroline official facebook page. Martin Fisher was re-tuning the amp coupling coils for 648 from 828 (i think)
all the best,
STx
Rod Watts
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