Need help to revive Rotovibe!!!

[Steve Conner]

Never, but I once spread mango chutney on my toast instead of marmalade.

[bob1]

Rotovibe

Steve
what other transistor do I check out to
see if its dead???
I fixed one of these, so I think
I can fix the second one

[Steve Conner]

Sorry, I know nothing about these pedals, we were just talking crp about polarity protection in general.

[52 Bill]

Bob1
Every broken pedal can have a different cause for not working. The fact that you fixed one by replacing the same thing that someone else did was just a lucky break. Rather than looking for the magic part to replace, why don't you investigate the problem and see where the problem lies.

Does the pedal not power up with either a battery or a power supply?

Have you tried reading the voltage from the battery to the pc board and then through the circuit to see where it stops?

The only schematic I've seen is for Rev.E, which doesn't have a Q7. But like a lot of pedals it has a power supply switching jack, a reverse polarity protection diode and a 9v regulator chip and any of these could cause your problem.

[Bassbuddy]

If it's a series diode, it takes 0.7 volt off the supply voltage, which the designer might not want. In particular, if the diode is also in circuit when the unit is running off the battery, then battery life will appear to be shorter.

A Schottky would solve this, but might break the budget for a mass-produced unit, where they care about the difference between a 5 cent diode and a 50 cent one.

If it's a shunt diode, it might burn out your power supply or fail short.

We're not dealing with a designer, nor with mass production here, but with one person trying to repair a (one) rotovibe. If a 2 cent diode can help him to prevent the same problem in future it's worth more than 2 cent. Even the cost of a (one) schottky diode would likely be worth it to him.

[Steve Conner]

Well, obviously there's nothing stopping you, the owner, from retrofitting a diode, and it might be a good idea if you have a pedalboard with jacks of both polarities that can get mixed up. (Though you still need to ponder the shunt/series thing.)

But I, and quite a few others here, design, build and repair electronic equipment for a living, and I guess we can't help looking at it from the other side.

In particular, Enzo likes to draw a line between "repair" and "re-engineering", and adding a polarity protection diode to a stomp box would be re-engineering. The end user can do anything he likes to his equipment, but a commercial repair guy aims to just get it working again. If he goes modifying things, it could cause other issues that he would get the blame for.

[xjbear]

I had a dead Rotovibe JD4s as well with a Rev D board and fixed it today!!!!! I did the 2N3906 in the spot next to Q7, it looked burnt, that didn't help so i bridged the mpsa18 in the Q7 spot, basically just twisted the tranny round and round till the leads broke off then put a drop 'o solder on the mess and it worked finally after 6 years am ordering a handful of MPSa18's cuz none are at Rat Shack, and will replace asap...thanks a ton...also fixed my Memory Man with Hazarai what a great week

am adding the keyword Rotovibe Repair so searches will find it quicker I hope

[J M Fahey]

We're not dealing with a designer, nor with mass production here, but with one person trying to repair a (one) rotovibe.

Sorry but I think you *are* dealing with a Designer (Jim Dunlop) *and* mass production (I'm sure he made at least 100 and very probably a couple thousand of them, plus many other products).
Now if it were the musician's own design, yes, I think he might find your advice useful.
And 0.7V "lost" are a lot, specially if your circuit would be much happier with 12 or 15V and barely works with 9V, which to boot do not last long.
Most pedals must be able to work happily with 8.5V or even less, to provide for a longer *useful* battery life.

[xjbear]

that post you quoted was a year ago....and he was comparing component cost from the point of the manufacturer and the point of the end user doing the repair. $1 for a part is alot to the manufacturer but $1 for a part is cheap for the consumer compared to the cost of buying a whole new pedal, there's your translation.
leave this thread to rotovibe repair please..it saved me a lot of money and is going to be very helpful to someone else I'm sure.

[J M Fahey]

$1 for a part is alot to the manufacturer but $1 for a part is cheap for the consumer

*where* do I speak about cost?
I refer to the very valid technical worry about voltage loss across a series diode, when the power supply voltage is already marginal.
Now that you mention it, please let me show my lack of enthusiasm about the solution you suggest:

just twisted the tranny round and round till the leads broke off then put a drop 'o solder on the mess and it worked

Oh well.

[xjbear]

not a solution sir...a stop gap measure to verify operation, and you aren't welcome to criticize...read the context of the actual post you commented on not what YOU posted. I DO have proper transistors on their way *read* ok we're done, no more on this subject unless you gimme a schematic for a protective diode circuit...pics or it didn't happen

[J M Fahey]

Will this do ?

* No voltage loss.
* Blows the fuse protecting *both* Pedal and PSU.
* Protects both against reverse DC polarity and AC.
Caveat: if user solders a piece of wire across fuse "as a stopgap measure until (already ordered) fuses arrive" it loses all effectivity.

As a side comment, please grow a thicker skin; this is a Forum full of bright, although slightly excentric people, each with his own view about problems and solutions, and posting an idea here is *asking* for criticism, that's the fun of it.
Read around a little and you'll catch the spirit of it.
Nothing personal and welcome to the Forum

[xjbear]

thanks Juan, nice and simple too, I appreciate you taking the time to post it. would be nice to just insert it in the b,c,e spots where the mpsa18 was. and yes I have been a little snarky lately sorry

[leepyringa]

I managed to temp fix my Rotovibe!
First, the only available schematic is not the same as my circuit at all, unfortunately.
The power, battery or external plug, feed into a MPSA18 which is an NPN transistor. The 9v feeds the collector with a 2.1K ohm resistor between collector and base. Very little power was getting to the emiter, so I simply pulled the transistor and shorted accross. Works.
Now I just have to buy a new transistor.
Bjornf2

Didn't work for me Any ideas how to fix my rotovibe ? guys?

Or maybe I did it wrong ? I plugged it with wrong polarity too , so i just opened it and desoldered the Q1 transistor and soldered together base , emitter and collector

Please help me ! I have a rev A version