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Thinking trimmers or the dip switches. Everything else is standard stuff (white box film caps, red mica caps, small ICs are dual op amps, the large IC is the bucket brigade chip). At least 1 of those trim pots will be the bias adjust for the BBD chip. Find a schem and all will be relatively obvious. ... fine...



I think those dip switches are for the line/instr selection (see top right quadrant in schem directly under the output jacks AND the matching switch on the input side, directly to the right of that note on the top left). Interesting feature.

 

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I'm with Granny on the dipswitches. Note that the schematic he posted uses a Reticon R5101 delay chip, while the pic shows a Matsushita MN3008. The Reticon chip is spec'd at 2000 stages, while the Panasonic/Matsushita chip is 2048 stages. Essentially the same, although the MN3008 takes up less space. The schematic shown would seem to be from a later-issue 3-knob unit. I have no idea what the more recent 5-knob versions are using, but an educated guess would be the MN3208.

Both Reticon and Matsushita went through pahses where the one ceased production of something that the other one continued making for a little while. Both Panasonic and Reticon have long since stopped making delay chips. Coolaudio - owned by Behringer - has resurrected the MN32xx series, and XVive, a Chinese company, has brought back the MN3005.

Note that, since the unit provides sum and difference versions of the chorus effect at its outputs (i.e., dry + wet and dry minus wet), there were no stompswitches available at that time, which could yield true bypass of a stereo effect. As a result, the original 3-knob version unit used a SPDT stompswitch to cancel the wet feed to the mxing stages. Later 5-knob versions would use a DPDT switch to do the same thing, and engage a status LED.

You can find more info about the chips here: Behind the Bucket Brigade | Premier Guitar
 
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