Vox 1902 Repair

[rineanna]

Anyone have any tips on how to troubleshoot a Vox 1902 Flanger pedal? I found it the other day but it's not working. Bypass is fine but there's no LED lighting or sound when it's on. No oscillation even. It's got the Reticon Sad-1024 chip which I don't really want to buy again unless that's definitely what's wrong with it. Anyone help?

[Anitoli]

Do you have a schematic for that?

[sikter]

It could be fried protection diode because of wrong polarity power supply connection.
Easy fix if just diode is dead.

[rineanna]

Here's a link to the schematic http://www.voxamps.com/downloads/circuits/1902flan.jpg

I'm hoping that it's a blown diode which I've had to repair on my Phase 90 before but I can't see any burning and I don't know which diode is the one for the voltage

[Anitoli]

It should be D1 zener although the schematic doesnt indicate value.

[sikter]

I would try with 1N4004.. Make sure you solder it correct way as the diagram shows.

[Anitoli]

To the OP, the schem shows two batteries in series. Is that what this thing takes?

[rineanna]

Yeah it takes two 9 volts. It says on the side of the schematic that D1 is an RD-16. If I jumpered it out to test it should it work?

[sikter]

Yeah it takes two 9 volts. It says on the side of the schematic that D1 is an RD-16. If I jumpered it out to test it should it work?

It should if no other compnents have died.
But if he was testing it using 9V DC power supply that would be probably be the reason why it wouldn't work.

Proper voltage is 18V DC, it could probably worked on 15V (more or less) but 9V DC is not enough

[rineanna]

No I was using two 9v batteries. I'll try jumpering the diode and let everyone know. Hopefully it works

[sikter]

Hm, if you were using batteries and wireing inside pedal
was original you shouldn't burn the diode in the first place.
Anyway you can always use it as a "mute-pedal".

[rineanna]

Well I actually found the pedal. Didn't ever see it working so I was hoping to get it going as she's meant to sound great. I tried jumpering the diode but still didn't work

Any more tips?

[Anitoli]

Yes, the push button switch appears to be a DPDT switch. Verifty that when the switch is in the on position you are gettin continuity across the connections.
If you have a voltmeter you can trace the voltage from the batterys point to point through the circuit. this might help.

The RD16 designation means it is a 16v zener diode used for voltage regulation. If you suspect it is shorted you can lift one end and see if the unit will work, although if it were something would be hot.

Also the output jack is a switch. make shure there is something plugged in or you wont see any power at all.

[rineanna]

I mightn't have had anything plugged into the output when I tested it. Let me try again and I'll let you know

[rineanna]

Just gave myself a nice 18V shock there

I clipped the diode and got the LED to light very faintly. Still no signal though. Bypass is fine and I noticed that if I pull out the battery then the pedal is engaged I can hear a small hiss through the speakers.