My Poor Mu-Tron Phasor

[gktamps]

Back in around 1976-77 I bought a Mu-Tron Phasor and used it for years in my various bands. In the late 1980's I let a friend "borrow" it, which he apparently took to mean, keep it and move out of state with it.

Well, a few years ago he died, and his wife saw my name in the box (I had the original box, paperwork and receipt) and tracked me down to return it.

That was incredibly nice, but turns out it had stopped working at some point (bad karma?) and he started to hack into it to "fix it". He did some electrolytic cap replacements but removed the switch assembly, leaving the wafer in place. I have not tried to work on it yet but have tracked down online schematics.

My question - does anyone on our lovely forum have experience working on these pedals, and have any suggestions about typical failure modes, problem components, etc.? I will start by checking the replacement caps then powering it up and checking the power supply, but I haven't been inside of this before so am looking for some available expertise.

Cheers,

Greg

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[Reeltarded]

I want to be funny..but..

Sorry about your pedal!





Let me call a friend and see what he says. I know he has fixed a few Mutron things.

[gktamps]

Thanks Miles!

And by all means. Be funny. Can't take this crap too seriously, right?

[thetragichero]

by far my favorite phaser. grew up playing my father's and it certainly ruined other phasers for me. these fetch several hundreds of dollars on reverb so definitely worth the time and effort to get it working again

[gktamps]

these fetch several hundreds of dollars on reverb so definitely worth the time and effort to get it working again

Thank you - yes I've noticed that. It has been so long since I've played through one of these I can't recall the sound, but hopefully that will change soon.

One of the 12V Zener diodes was bad, so I replaced both, as well as the rectifier diodes while I was in there. Now it has stable, pretty close voltages on both rails.

One odd thing is the guy replaced the output decoupling cap with an electrolytic - 10uF 16V (yellow one in photo) - but it seems an odd place for an e-cap, and seems like a large value. This should just be a DC blocking cap, I am thinking, so seems like a strange choice. The schematic is too fuzzy to see the type or value.

Now my problem is I can't find a switch body in my piles for the wafer switch so I will have to sub in an open 3-way switch for testing and initial use.

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[gktamps]

Huh. Just looked at the more legible schematic for the Bi-Phasor, and the output cap value is 10uF/16V, but looks like a non-polarized cap. I'll have to order one of those, and get the switch sorted out, then see if that does the trick.

[thetragichero]

regular old electrolytic should work as long as you get the polarity right
here you go, in two nicely redrawn pages: https://www.diystompboxes.com/smfforum/ ... ic=64801.0

soundwise, what stands out is that it sounds "creamy" to me. that could just be noise that's getting phasored but i like it

[gktamps]

Found a BP 10uF so I'll just stick that in there. The schemos you linked are for the Phasor II, which has a different circuit and components. I just found a clearer print of the first model, and the values are pretty legible.
Thanks!

[Reeltarded]

Well, I just won't answer that callback.. you are over half-way there!

[gktamps]

And... done!

Replaced all electrolytics and diodes, as well as selector switch. Sounds '70's awesome! Great range of phasing tones, pretty darned quiet, no bad habits.

It is one of the crappiest quality PCBs I've ever worked on - the traces lift with almost no heat or pressure on components, and I have a lot of experience working on delicate PCBs now. Only good thing is it is single-sided, no through-plating.

It's been so long since I've played through this or heard another one - what a treat. Not sure I'll keep it as I rarely use pedals these days, but now it is in fine condition for the next player if I sell it.

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