problems with a Dunlop Rotovibe

[mr_doyle]

hi all

i've got a broken Rotovibe, wondering if anyone could help me out.
I can't find any schematics out there, nor Dunlop is selling them anymore.
After some components replacing, current now reaches the J176 transistor, but then i've lost its trace.
I've checked out ICs and they are ok, same for Caps and resistors.
Leds turn on/off but no sound is coming out of the fx.

Any input appreciated.

Thanks in advance,

D.

[Ry]

Welcome to the forum!

I've been fielding the Rotovibe questions as best I can.  No, there is not a schematic online or anywhere else that I've seen one.  I haven't heard that anyone has managed to repair one either, but I'm more than willing to help out.

Have you read the Debugging Page?  The link is at the top of the forum pages.  It talks about using an audio probe to trace the signal through the circuit.  I highly recommend using this method.  You will need to determine where the signal should go by looking at the circuit and the data sheets for the chips in it.

It sounds like you're off to a good start, having gotten this far.  What did you replace?

I may have to take my rotovibe and trace out the circuit over my christmas vacation.  This topic has been coming up a lot lately.

Ry

[The Tone God]

I may have to take my rotovibe and trace out the circuit over my christmas vacation.  This topic has been coming up a lot lately.

I've been thinking about the samething. I have the board from the rotovibe that I gutted. If you want to give a shot go ahead otherwise I may do it with some of my spare time which I have little of.

Andrew

[p1_ind]

I had a friend that had the same kind of problem with his Rotovibe.
I tried changing some of the ICs but that didn't fix it.
Then I was also coming to a JFET on his that I suspected as the problem,
on his the JFET said J175.
So I ordered one and replaced it, no luck.  Then out of curiousity I put
a J201 in it and it worked.
All  the info I found says that a J175 is a P-Channel JFET and a J201 is
a N-Channel.
I told my friend what I did and he said "As long as it works its OK with
me."
So you might try that, I'm not saying that is the proper way to fix it but
for me it worked.

Adam

[Ry]

I will take it and a multimeter with me on vacation.  If I get time, I'll give tracing it out a shot.

Ry

[mr_doyle]

thanks to everybody guys!

I tried changing some of the ICs but that didn't fix it.

+1

Then I was also coming to a JFET on his that I suspected as the problem, on his the JFET said J175.

me too, but mine was a J176

So I ordered one and replaced it, no luck.  Then out of curiousity I put a J201 in it and it worked.
All  the info I found says that a J175 is a P-Channel JFET and a J201 is
a N-Channel.
I told my friend what I did and he said "As long as it works its OK with
me."
So you might try that, I'm not saying that is the proper way to fix it but
for me it worked.

i'll try this of course!

i suspect the source of problem was a wrong power supply.

thanks again guys!

D.

[gluedtogether]

I know this is an old post, but I found the same problem with a rotovibe and after trying everything else, found this post.  I just picked up a broken Marshall Vibratrem for $5 which doesn't work. the Led does, but no sound. the circuit seems similar to the rotovibe, without the expression pedal.
I just got the schematic from Marshall and low and behold, there are two J176's I am going to try replacing those with J201 and see if if works.

I will post if it does

[lovric]

search some more around here, ~jc mailett posted some hand drawn schemes.

[Joep]

If you suspect the power supply it might be an idea to check some voltages. The IC's are probably opamps so check the voltages at the supply pins. On an 8 pin DIP opamps it's pin 8 that should be reading around 9V (in case the Rotovibe runs on 9V).

Joep