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These modules were re-capped and cleaned, with a lot of tidying up to be done on some of them.
The original modules had two balanced input stages for the console group output and the tape return. A third audio stage was used as a driver for the console meters.
Two relays (called "SYNC" and "PGM") were used to select between the two input sources and configure various fader and meter modes. The third relay was for the MUTE and SOLO-IN-PLACE functions, driven by switching and transistor logic.
The original 2046-094 Channel Input Module used an ancient uA739 14-pin dual op-amp IC for the balanced input stages, buffered by some API 077 discrete transistor modules to drive the faders.
These modules had been modified by a previous owner to replace this IC with an 8-pin NE5532 IC and eliminate the buffer modules. A later version (2046-094-C) did away with the buffer modules and went to a single sided board.
In this incarnation, the two line inputs originally used for the console group output (PGM) and the tape return (SYNC) were designated Line 1 and Line 2.
The SYNC Relay was used to select Line 2 input. The PGM relay was not used. A simple wiring change made all sends PRE fade. On the mainframe, the master PGM line was connected to ground to disable the PGM relay. If necessary, the PGM relays could be removed and used as spares. If this is done, a single link must be installed.
The relays fitted were not the originals and had adaptor boards to fit them in place of the original relays. There were issues with intermittent operation of these relays and it appears most of these problems were caused by poor soldering of the adaptor boards and cutting the relay pins too short. Many of these had to be repaired, consuming an enormous amount of time.
The retro-fitted relays were relatively large and clunky but they were efficient (low coil power consumption) hermetically sealed types (indicated by the yellow casing), making them reliable.
Ironically, the relays on the other monitor section I had to work on were the originals and had very few problems!
This bulky board contained nothing but illuminated switches and the mix summing resistors. These boards were completely original, with no modifications.
These boards were cleaned and all switches cleaned with Caig Laboratories DeOxit D5 spray.
In most API consoles, the lamps are run on a considerably lower voltage than their nominal 24V to reduce power consumption, lengthen their operational life and prevent the operator from being blinded by excessive light!
These consisted of a set of four API 2520 modules driving output transformers, capable of driving balanced or unbalanced 600Ω lines.
These boards were used extensively in the console main frame and were configured in different ways for specific applications. As summing amplifiers (in API terminology "ACA"), the board was configured for "virtual earth" inputs (no input resisitors) and connected to external summing resistors (such as the ones on the 2048-143 Channel Assign Boards). As buffer amplifiers (such as console fader returns), input resistors were installed on the board. The feedback resistor/capacitor combination set the overall gain and varied with different versions.
On these boards, the capacitors had been replaced some time around the late 1980's/early 90's with Panasonic types. As has been seen in many vintage consoles 20 years on, these capacitors had leaked acid all over the boards, damaging tracks. The burning sensation when handling these boards underlined the problem! The capacitors and other damaged components were removed and the various damaged tracks were repaired. These boards were so bad, there was only one solution - wash them in water to neutralise the acid, drench with DeoxIT D5, then thoroughly clean and dry...
The output transformers could be configured in different ways. In this incarnation, they were configured with a ratio of 1:2 for driving a single +4dBm output. A 2-pin connector was added for an unbalanced output (pre-transformer), which was used by the monitoring section.
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The mainframe wiring was in a bit of a mess, due to work and modifications done over the years. It must have been a bastard trying to work on the thing on your back from underneath the console! Wiring around the Channel Input Board connectors was repaired and tidied. The wiring loom was untied and redundant cables removed. The remaining audio cables were re-loomed and wired to the Rear Panel DB25 connectors. Most of the wiring on the mainframe passes between the motherboard and the Line Output boards. 
Summing Resistor Board
The small board was for summing signals from the main console. New summing resistors were added for the 8 signals from the Sub Input Board. 
New loom to connect the line outputs to the rear
panel.
This custom loom configures the 10 Line Outputs to the Sends connector and Line Output to DAW connector on the Rear Panel. |
