univibe fix

[john3696]

Hey,  I have a question for you guys...I found a dunlop univibe at a garage sale this weekend for $5.  I figured if I couldn't fix it I could scrap it for parts since it looks in good condition.

well I put the 18V through the pedal and my signal goes through to the amp with the pedal on or off.  the Volume pot works when the pedal is on but none of the other pots work(speed and intensity) and both the switches seem to work(light the leds when switched)

It looks as though someone might have spilt something on it once since there is a little bit of rust on the Speed Pot and some of the solder joints.  now I have only built a few small pedals and I don't truly know what I am doing, I can just follow diagrams and instructions well.  

so what would be the first place to look to find out what is wrong with the circut?  or would I just be better off scraping the pedal?

I think I am going to desolder and resolder the rusted joints and replace the rusty pot first, but after that I would be stumped...

thanks for your help :?:
Graham

[Torchy]

Firstly you should read this http://www.geofex.com/Article_Folders/univibe/uvfrindx.htm carefully and understand how the vibe works.

Then you could read this http://www.lynx.bc.ca/~jc/pedalsUnivibe.html

I would say they bulb will have blown for an easy starter. If the bulb doesnt light then the vibe does nothing (the Cancel switch actually switches off the lamp driver tranny) but buffer the signal. Buy a couple of bulbs while you're busy Turn the lamp trimpot to maximum resistance, power the vibe up and slowly decrease the value of the trimpot. If the bulb doesnt glow then your driver transistor has probably gone. Replace with a 2N3904 and try again.

Lots of people with more knowledge than me around here so post back with results

[Chris R]

Interesting read.  I didn't know the old univibe had 2 inputs.  I bought one a few years back.. and it only had 1 input.  

Is there an advantage to have 2 inputs ?

C

[Torchy]

Pedal sharing ?  :wink:
Honestly dont know why two inputs ....

To help the original problem, if you dont get it working with new bulb/driver tranny then d/l
this http://www.generalguitargadgets.com/v2/diagrams/neovibe.pdf and check the
voltages given on the circuit diagram.
You should have roughly the same on your vibe. The LFO is (I think) where your problem is. Maybe. Probably.

[gez]

would I just be better off scraping the pedal?

$5 for a Univibe?!  You jammy sod!  Personally, I'd stick with it and try to bring it back from the dead.  Even if it means replacing huge amounts of the original circuit it'll be worth it (and a great learning experience).  

I've never had the privilege of working on one of these babies, but I'm sure many here have and will offer advice.  Good luck!