Vox Cambridge 30 disaster

[guiguy]

The opto-coupler was notorious for causing various faults in these units. You could just try bypassing it. You will not have tremolo, but if the 'bad' sound disappears, then you know it was caused by the opto.

Did you happen to know off the top of your head which pins I should bypass?
Cheers
Pat

[g1]

Upper right area of schematic, right of IC3. R41 connects to one leg of opto, R42 connects to another leg.
Those 2 points should get connected for bypass test.

[guiguy]

Upper right area of schematic, right of IC3. R41 connects to one leg of opto, R42 connects to another leg.
Those 2 points should get connected for bypass test.

Sorry it has taken me so long to get back to this.
I bypassed the opto-coupler and the amp got really really loud!

So...I bought an opto-coupler. The only one available around here was a Fender one (16282).

I replaced it and the amp got quieter!

SO, I took it out and scratched my head.

I tested the voltage accross the led side - nothing.
I tested the voltage to R59 and from the voltage supply and ground and it was about 5V

I cut the opto-coupler appart and re-installed it to see if the light was doing something.
The amp got loud (because the sensor was exposed to my bright light) but the bulb in the thing was doing nothing.

I installed an led in the hole and it just barely seemed to light up ....only enough to see a line of light.

So! Any ideas?

Anyone ever see this? I am guessing that maybe ic6b is not providing a ground to the opto coupler bulb?
or could ic4a be involved?

Ugh
Pat

[g1]

That Fender opto won't work right. You need the proper one. I'm not sure where you can get it.
I think there was another post about it recently.

[The Dude]

If I'm looking at the right thing, the supply side of R59 should be 9.1V- and you have 5V? Is that correct? Check directly at the cathode of ZD1. Do you have 9.1V there? Do you have 15V on the cathode of ZD3?

[guiguy]

If I'm looking at the right thing, the supply side of R59 should be 9.1V- and you have 5V? Is that correct? Check directly at the cathode of ZD1. Do you have 9.1V there? Do you have 15V on the cathode of ZD3?

Yes, I have 9v at one side of R59 and about 5v on the other side.

[The Dude]

Well, never mind. I misunderstood your post. Sorry.

[g1]

The fender won't work as it is a neon type.
VTL5C3 type will work. (see post #4 & 5 here: http://music-electronics-forum.com/t46528/)
You can get them from small bear or ebay:

Photocoupler XVive VTL5C3 Work-alike - Small Bear Electronics

https://www.ebay.com/itm/Xvive-Audio...19.m1438.l2649

[guiguy]

That Fender opto won't work right. You need the proper one. I'm not sure where you can get it.
I think there was another post about it recently.

I bought it because I found at least three posts that siad to use a Fender one. Either way, should I not have voltage between the two holes where the light attaches to the circuit board? I dont get anything.

[Enzo]

Look at the schematic, it depends how you have VR12 set.

[DrGonz78]

I bought it because I found at least three posts that siad to use a Fender one.

That's odd. What site were those posts from?

[g1]

That's odd. What site were those posts from?

Yes it's very odd. Someone may have recommended a fender LED type opto from the red-knob style amps. But the fender 16282 is a neon type and will not work in this circuit.

[guiguy]

Yes it's very odd. Someone may have recommended a fender LED type opto from the red-knob style amps. But the fender 16282 is a neon type and will not work in this circuit.

Well, you are right about that! I bought one off ebay and it did the trick!
Thanks for all the help, folks!
I still have to put it through it's paces but it sounds clean and loud and now the trem works as well as ever.