by GordoGibbo » Sun Mar 31, 2013 6:20 pm
Well gents, the more I dig into this old girl the more it's beginning to make a little bit of sense to this untrained eye of mine. Having the schematics helps, and I've poured through them...and with every pour-through, even though most of it is Latin to me, a little bit is coming into focus.
Even though it doesn't have a full complement of modules, there are enough there - as Mike suggested - to get by with, and more on that in a minute.
What I am missing is a small transformer identified as being in position T 11 and is identified as a transformer that feeds the cue system. I'm also missing something called an AT 263A, which goes in at position A 19 and is identified as a monitor amplifier. So what this suggests to me is that I won't have a working cue system, or talkback (probably, but I don't need that anyway for the moment), or what I would need to drive a monitor. I just wonder if, without those two pieces, there will not be anything to drive the headphones.
I'm also missing what appears to be two, out of four power supplies. Mike Cleaver thought, based on memory, there was one or maybe two power supplies...either both to drive the thing or one serving as a redundant. There is a massive transformer, identified as going into position T 28, that is said to drive all the power supplies. But that said, there appears to be four power supplies, or which I only have two.
Here's what the book says: "There are three PS 878 48 volt regulators for program, monitor and cue amps." These are identified as PS 2, PS 3 and PS 4. I'm hopeful that the order in which they were described...ie, 'program,' 'monitor' and 'cue' is in order and therefore corresponds with the numbers...ie, PS 2 would be 'program,' PS 3 would be 'monitor' and PS 4 would be 'cue.' That would make sense, wouldn't it?
The fourth power supply is actually the first one that is identified as PS 1 and is described as PS 877, a 36-volt regulator for input and booster amps.
The book also says this" "A separate 24-volt dc unregulated supply is provided for dc control. All supplies are fed from transformer T 28."
What I am missing are the supplies that sit at position 1 and 2. I have 3 and 4. Thus, I need a PS 878 and a PS 877. I suppose, since 2, 3 and 4 are all PS 878s, I could harvest, say, #4 which I assume drives the cue circuit (I'm missing the transformer anyway) and move that one into PS 2, which I would assume drives the PGM circuit, which is what I would need, bare bones, to get the board operational. That just leaves PS 1, which is the PS 877...which appears to be an important one....
As for modules, as I said at the top most of them are there, and thanks to the schematics I can figure out what slots feed what. I can also look at the front of the board and judging by what the tags / labels say for the specific channels, I can tell what that channel was used for.
Channels 1 - 3 on this one were wired for carts, tape decks etc. And the slots contain MT 244A modules, which are described as being appropriate for matching high level inputs. CH 4 is the CR mic channel, and it had a lone AT 240 sitting in the 'stereo right' slot with nothing in the left. I don't know what an AT 240 is, but going through the manual the AT 240"A" is a pre-amp designed for low-level inputs. There are other areas where they have 240As for mic inputs, and there are various references throughout the manual to this affect as well, so I've come to the conclusion that the 240A is the appropriate module for microphones.
They also had CH 7 on the front of the board ID'd as a mic channel, and lo and behold there was a lone AT 240A in the 'stereo right' slot (nothing in the left, or the top row of the two-row rack).They also had an AT 240A sitting in stereo left of A13, which appears to be the stereo record bus. Nothing in the right. I don't know if there was a reason why the right-hand side was empty, but again....the bottom rack, which is a bit more difficult to service, was completely full of modules while any of the missing ones were from the top rack - which is more accessible - so my guess is, the modules were harvested for the other, twin to this board they had, once this board was decommissioned.
Anyway, I don't anticipate using the record bus of the board for anything....unless, of course, I start up an internet radio station someday and therefore cannot interrupt the program to record a weather forecast or something on record bus. So...just for fun, I removed the lone AT 240A from the record bus (left) and also removed the lone AT 240A from the right side of CH 7 - which was identified on the board face as a mic channel. I then swapped out the lone AT 240 from the R (bottom tray) of CH 4 and I now have to AT 240A modules in CH4, which is wired as the main CR mic.
Makes sense to me. And here's another reason why I think the AT 240A is the preamp, and thus appropriate for microphones. In the A10 slot, which is identified in the schematic as being the PGM BOOST, they have two AT 240As sitting there. Beside them, at A9 which is identified as BUS IN, they've got two MT 244A modules sitting there.
Thus, it seems that if and when the day comes that I get this puppy up and running, after it's been recapped and given the once-over by some kind of professional, I will at least have a working mic channel with two AT 240A modules left and right in CH 4.
Here's the thing. Remember when I said CH 4 originally had a AT 240 (no "A") sitting in the Right slot (bottom tray), with nothing above it? Well, when I pulled the module out and looked at it, someone had written this on the side of it: "Modified for phase reversal (underlined), June '76." Does that mean there is a problem with phase reversal in CH 4 and they had to modify this particular module to compensate for it? Or was there a problem with the module itself, so they had to modify the module just so the module would play nice?
And because there was an empty slot above it, I don't know what was in there....whether it was another AT 240 or an AT 240 A. There are no other AT 240 modules in the console, just the one. The remainder are AT 240 A, MT 244 A and three AT 242 A modules sitting in PGM LEFT and PGM RIGHT, and what appears to be RECORD BUS mono at A13.
Anyway, that's my story for tonight. Looks like I'm looking for the four pieces noted above....the AT 263A that sits at position A 19, the small transformer that sits at position T 11, and the PS 877 power supply that sits at PS 1, and the PS 878 power supply that sits at position PS 2.
Have a great evening....
Gordo