BBD Dead?

[Jack]

I have an original ibanez FL-9 that does "turns on" but doesn't flange. Is there a way to check if it's the BBD?
Cheers

[Mark Hammer]

Possibly.  A problem which occurs often enough to warrant consideration is that the trimpot (usually used) to set the bias voltage on the input to the BBD has become jarred or movd from its original optimal location.  The BBD needs the audio signal to "ride" on a DC voltage supplied by the bias.  More, or less, than that voltage and you don't hear anything from the BBD.  You can tweak the trimpot without damaging the BBD.  If all is behaving "normally", you shold hear no BBD output, then fuzzy, hazy output, and finally clearer BBD output and then hazy again, as you rotate the trimpot.  It is possible to nail an optimal setting by ear in this way.

Alternatively, the FET which enables/lifts the delay path from the mixing stage at the end might be shot for some reason, and essentially "stuck" in the off position, despite the rest of the circuit (indicator LED, etc.) looking okay.  Identify the FET in question (often a K30)and jumper the drain and sourc to try out this theory.

[Jack]

after adjusting the trimpot there is now flanging but only in the "background", very faintly, that responds to the controls. Unfortunately I have no idea how to identify the FET. If anyone has a schematic that would help A LOT.

Cheers

[Mark Hammer]

Tell us what the numbers are on the transistors that ARE on the board, and I'll tell you which one is which.  Note that transistors starting with 2SK 2SJ or K or J are FETs, while those starting with 2SC or C are not.  That info will probably help you nail it easily.