Mu-Tron Phasor repair help {+ edits}

[smnm]

So - I 've just got this Phasor. I knew it wasn't working but hoping it's something easy.

Opening up I find, 2 connections to 3 way 'rate' switch are broken - easy fix.

But in the process of getting the board out two other brittle wires break - the green wire from the pole of the rate switch, and the output jack
- any clues as to where they go?

Candidates are:
point no 1 - from the trimpot {EDIT: seems like a good candidate for the switch pole I think}
point no 2 - from a 560 ohm resistor connected to 10uF cap {just noticed this is also connected to the bypass switch - so is going to be the output}

There's also a 3rd choice, which is a spare ground point - this had no broken wire in place but had been soldered at some point in the past {the output ground lug has no connection - it's grounded throught the case, maybe this was an optional extra ground for the output jack ring?}

Sorry if this is OT and dull, any encourangement IS appreciated.



Thanks

Simon

[smnm]

well _ I made these connections but it doesn't work.

I know the jack connection is right though as I get the bypassed gtr signal, but there could be any number of things up with it that are beyond me, there is crackle and noise when I move the power cord (so that should be replaced), but the AC goes into the transformer and comes out at about 20VDC on the other side at least ... seems like I'm looking for a repairman now.

[Unbeliever]

Simon, the schematic I have for this device is pretty much completely unreadable, but it's true that the Phaser II is very similar to 1/2 a Mutron biphase. That said, I can just make out that the output is hard-wired to the 500 ohm resistor connected to the 10uF cap (I presume this one is a NP cap), then on the other side of this cap is an 18k (I think) resistor to ground, along with the pole of the footswitch. The throws of the footswitch are connected to the output of two different opamps, one the 'output' of the circuit and the other a buffer.

The schematic I have must be for a different version of the Phaser II coz there's no rate switch, however a rate switch usually switches in out extra capacitance to adjust the LFO rate (if this is what it does) so hopefully you can suss it out.

[Unbeliever]

Hmmm ... I'd be happy to look at it and fix it for nothing (so we can get a good schematic), but if you're in the USA then you'll need to cover overseas postage one way. Otherwise, I'm sure we  could get it working. Is the LFO sweeping?

[Gus]

I often draw a picture or take a picture  before I work on something an effect,car etc.

I have worked on a few older Mutron effects The "fix" was repairing bad solder just like R.G. has posted at his site.

What phasor is that one?  I don't see a photo cell assembly.

[Unbeliever]

What phasor is that one?  I don't see a photo cell assembly.

The metal cans - 6 stages worth.

[Gus]

6 photo cells?   IIRC The two I worked on had one assy containing the 6 photo cells, interesting. 

[Unbeliever]

Sounds like you were working on a Biphase - they have an (incredible in my opinion! ) metal can arrangement with 6 LDRs arranged around a single LED. There's pic on the net somewhere...

[Gus]

I have repaired a real Biphase yes they are cool.

the mutron IIs I worked on had the same assy IIRC it was years ago..

[Processaurus]

Which model do you have, Mu-tron Phasor, or Phasor II?  The II's optical, the original is FET based I believe, and a totally different circuit from the II.

A possibility exists there is more wrong than than the broken wires.

While its open you may want to replace the electrolytic caps, they're about 30 years old and could possibly have dried out some.

I have worked on a few older Mutron effects The "fix" was repairing bad solder just like R.G. has posted at his site.

Me too!  Just touched up each solder joint with a little bit of fresh solder, and replaced the electrolytics, and voila, good as new.

[smnm]

Uh - I thought I replied to this last night, but it's not here, so: take 2

I looked at the solder joints, tested some, couldn't find anything suspect, I also tested for voltage at various places (successfully) but with a circuit this size (when I'm used to simple fuzzes etc) it's too much for me to do much more with any certainty. I'm in the UK, and this is a 240V version - Unbeliever, I'm sending you a PM.

Thanks all

PS it's the first 'Phasor', not the II, looks like this one


Simon

[Processaurus]

Hi Simon, I responded before but I guess it got lost in translation?  Anyway,  a cold solder joint is hard to see visually, and sometimes its hard to spot a cracked one too.  I reccomended just going through the board, and patiently touching up every solder joint with a little fresh solder, so they are all shiny and new looking.   It sounds like way more of a pain than it is, but I couldn't see it taking more than 5 minutes, since the board is out of the box.  15 if you have electrolytic caps of the same values to replace the old ones.  I did this exact procedure (joints and caps) and brought a dead Mu-tron Vol/Wah back to life.  Sounds like the same worked worked for Gus.

good luck

[smnm]

Thanks Pro,

It's back in the case now (typical me), but I'm probably waiting for a schematic from schematicconnection.com before I send it to Unbeliever. That will take a week or so, I should try this first - I'll take a picture and mark them off as I go. I think I have the caps I need.

S

[Peter Snowberg]

I just fround my Mutron Phaser so if you still need answers, just ask.