meaning of "FB" symbol on circuit board

[dragonfrog]

Does anyone know what sort of a component would be indicated by PCB labels "FB1" (and 2 and 3)? It would be a two-lead component, about the size of a standard through-hole resistor. The printed symbol on the board is just a thick line (the other symbols on the board are pretty standard - it has zigzag lines for resistors, and so on)

The background: I recently acquired a Suzuki Omnichord OM-100 (a kind of analog electronic autoharp. They're pretty cool). On dismantling it, I saw that one chip, I'd guess the ROM with the OS, was labelled "Omnichord 100/200", and that there were unpopulated spots on the circuit board to supply the features of the OM-200. So, my guess is that the OM-100 and OM-200 used the same OS and board, just the OM-200 used a fully populated board.

Most interesting to me, the OM-200 had some simple MIDI output capabilities. And right there on the board, it looks like just a few components are missing to add MIDI out to my OM-100.

For the resistor values, I'm sure I can figure out sane default values. But for the "FB*" components, I don't even know what they might be.

I could just use jumper wires I guess, as most MIDI schematics don't seem to have anything but an overcurrent resistor or two. But I'd at least like to know what I'm leaving out.

Thanks
Mark

[Danno Gee Ray]

Ferrite Bead?

[dragonfrog]

Yes, that must be it, thanks! Explains why I don't see them on other MIDI schematics, too, since things usually work fine without them. Piece of wire it is!

[badstatic]

Interesting, my omnichord OM-27 also has an un-populated area of the PCB. Mainly it's missing 5 X '4069's' and a bunch of transistors........... any idea what these missing components will do?

[Sam_Zen]

The 4069 contains inverting buffers.
So in combination with the transistors, it stays quite unpredictable what the function would be.
Better check which signals on the PCB are connected to the inputs, to get a clue.
You can find the pinout here :
http://www.kpsec.freeuk.com/components/cmos.htm#4069

[dragonfrog]

That's very interesting.

That there are 5 (!) of the 4069s makes me wonder if they might be used for sound processing, rather than logic - that makes 30 inverting buffers, it seems like an awful lot unless you were doing something to polyphonic sound, using several buffers per voice.

Are there other 4069s on the PCB, or are those 5 the only ones?

Another that arouses curiousity - this site (http://www.klangbureau.de/Omnibend_E.html#chip) suggests the OM27 chip was capable of generating chords in all 12 keys, though the buttons are only there for 9 - maybe some supporting features for the other chords not implemented?

I'd echo what Sam_Zen suggests, trace out the circuit on the PCB. Trace back from the inputs, as well as forward from the outputs - where the signals eventually end up getting sent might tell you something...

[Danno Gee Ray]

It's likely that this circuit board was used for more than one model of the instrument. Might I suggest you find other models and see what the difference in functionality is? If the same ciruit board is used for more than one model, a simple omission of components may constitute a less expensive model. Inclusion of ALL the components could then be used for the high end, or "Flagship" version.

It is cheaper to manufacture a line of product when a single board is used in this manner.

[dragonfrog]

For later versions of the Omnichord, that's definitely true, Danno - by simply adding a DIN jack and a few resistors, I did get MIDI out from my OM-100.

So, if you can sort out the differences between the OM-27 and the next model, I think the OM-38, maybe those are candidate features...

[electri-fire]