Circuit Overview:
Organ and Synth like Trilogy but without string section or presets. The Organ has 4 drawbars of 16, 8 , 4 and 2 foot stops and the TDA1008 Divider/sustainer chips can deliver the tone mix through the separate volume control. Meanwhile the pitch generation has two 74LS221 oscillators as with all Crumars from DS-1 on pretty much, to create two time bases which can be altered with a fine pitch control for osc 1 and a coarse for osc 2. THere is also a glide with it's own CEM3310 EG though it only uses the attack segment I guess really. The 6.2V supply is attached to the buss wire so that every key that is hit has that voltage on it's wire. There are 3 boards, each having the dividers/sustainer facilities for 4 notes. ANd each note has two dividers; one for each of the two oscillator sources. The 6.2V from an activated key branches with three diodes. One diode allows current to flow to a 'gate' buss that is common to the diodes of the other notes that are grouped together for the particular 'channel' we are talking about. C and F# are channel 1. C# and G are channel two and so on til we're at F and B for channel 6. Anyway the gate then for a particular channel goes to 6V roughly or a bit less if any of the notes associated with it (eg. any C or F#) are being held. Also at the branch is a line whose diode charges a 4.7uf tantalum capacitor and that voltage is used to activate the output of the TDA1008 divider/sustainer chip for that particular note. Well actually both chips are paralleled for the two oscillators of that note on this line. The third diode goes to a series capacitor which allows a pulse through to the 'trigger' input of the CEM3310 EG chip on that particular channel. THe gate tells the same chip when it's time for the release envelope segment.
Service Tips:
Follow the divide down troubleshooting proceedure with missing/noisy notes and so forth. These parts being under the keyboard on Trilogy and Stratus. Missing groups of notes would be a bad VCA or something on a synth card. (Eg. no C and F# would be card 1. etc.) Beware though I had a LOT of connections on the motherboard for the analog boards go bad. Trace breaking right near where the interconnects are. Another issue I had wer CEM3310 chips that were latcing up. ie. they'd hold the level high til I release all the notes on that channel! I put in a different chip for those two channels and all was fine. It was intermittent. Dirty key contacts may also cause bad triggering of course. They must be very clean on this unit! Also one tantalum cap leaked a bit and was causing TDA1008 not to stay open long enough for the long release envelope to play out on that particular note. Many hours on this one. I retrofitted a Yamaha D80 keyboard into it. I had to put my own buss bar in because the conductive rubber contacts yield too slow of a rise and create sporattic triggering of the EG's. IT's also slightly narrower and wound up a little higher so I had to do some case mods. What a pain. :-)
Parts:
Lots of discrete parts but likely some oddball ones. Ask if you need a specific part.
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