Mutron Bi-Phase Optical Switch Question

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pmkipp
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Post by pmkipp »

Trying to repair a '78 Bi-Phase. The B side does not work. Dry signal goes through, no effect. LED on that side does not light up. Footswitch was tested and works fine. A-side works perfectly and sounds amazing. Took apart, removed the B side LED and it is dead. Removed the optical switch (which is in the same circuit) and it is dead. Measured the same voltage going to the B side as goes to the A side. So, what do I replace the opto-switch with? Don't mind making one, but cannot find a similar LDR. I removed the LDR side of the optical switch on the A side, and tested it with the circuit on and it tested at about 1k. Got no reading when the A side LED is off. So, do I need an LDR that is 1k light and infinite (or very high) resistance dark? I know I can adjust a trimmer if things are off a bit, but am hoping to get as close to original as possible. Thanks.
Pete's Pedals
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CheapPedalCollector
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Post by CheapPedalCollector »

Didn't they use VTL5C1 in that? Should work I guess.

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pmkipp
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Post by pmkipp »

Those are rated at 20k light, but on further reading I think the resistance goes down if the input current goes up. Probably need another trimmer in place of the stock resistor - thanks. Those are easy to come by.
Pete's Pedals
St Louis, MO

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PMowdes
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Post by PMowdes »

You'll have a hard job replacing the opto pot, but that just controls the depth if I remember correctly. You should be able to get side b running by shorting the footswitch pad to ground

I'll have a dig around I have the schematics somewhere

Have a look at the builds on deadendfx.com
We have the original and a modified version that does away with the need for the opto pot.

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ppluis0
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Post by ppluis0 »

pmkipp wrote: 11 Oct 2021, 23:47 So, do I need an LDR that is 1k light and infinite (or very high) resistance dark?
Hi pmkipp,

You can try building a DIY optocoupler using a 5 mm high efficiency led and one LDR facing each other into a piece of heat shrink tube.
Image

The photocell (AFAIK) with lowest resistance when are illuminated -using a green led- is the 5506

https://juriedengineering.com/products/ ... istor-5506

Let us know if this help to repair this unit.

Cheers,
Jose

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PMowdes
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Post by PMowdes »

Nearly all of the Biphase schematics are here.......

http://www.crazy-patroche.com/article-m ... 52497.html

The expression pedal schematic is here

http://www.freestompboxes.org/viewtopic ... 86#p162986

There is a mistake on the crazy patroche schematic

The pedal input should be J6-4 (the input that runs into R78 / R79 / IC216A - 3)

J6 pins should be

J6-1 > GND
J6-2 > Phaser 2 switch
J6-3 > Phaser 1 switch
J6-4 > Expression pedal in / out
J6-5 > +15V decoupled

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