24mm pots and a Mestro Phaser

[Timko]

My amp tech gave me a vintage Maestro phaser MP-1 to repair (the ones in the silver metal box).  He said the effect doesn't go slow enough.  And sure enough, the first part of the Speed pot has no change on the effect. I assume that the pot may be worn out and needs replaced.  For those who have worked on vintage effects, is this something that may be true? 

Also, the pot that may need replaced is a panel mount 24mm Reverse Audio 1M with a pretty long shaft.  I've been searching around for an exact replacement, but I've not had luck finding one.  Should I opt for a solder lug pot and connect it myself, or is there some place I could find something like that?

If I fix this, he said he'd tune up my Magnatone Varisty from the 50s, so I'm trying really hard to get it working for him .

Thanks!

[Scruffie]

Pots can wear out or suffer from skips etc, yes. You might be able to repair or replace the wafer rather than finding a replacement pot depending on its construction.

http://www.geofex.com/article_folders/potsecrets/potscret.htm

Of course, it could be something else in the LFO circuitry causing strange behaviour, perhaps the electros have gone bad.

[Timko]

After some more testing, I am pretty sure the pot is shot.  I disconnected it from the board, and realized that someone before me had spliced the pot into the traces after burning some of them out. 

After talking with a guitar tech / synth restorer in Seattle, I've decided to try the replacing the wafer thing as the shaft and thread size would be virtually impossible to find today.  However, finding a 24mm 1M-C pot is proving trickier than anticipated.

[Scruffie]

Yeah I've been down that road before, you'll probably have to keep an eye on ebay for used lots of old potentiometers.

It's not ideal but the rate pot is more dependent on taper than the 'balls' so you could switch those around and try out a standard log or linear for the feedback which are a little easier to find in 24mm.

You can also try and repair the wafer (I know pinkjimiphoton uses a pencil to do it) but perhaps if it had been fiddled with before, that might have already been attempted and failed.

[Bio77]

Does the wafer have to be 24mm?  Depending on the geometry of the wiper, maybe a 16mm wafer would work.

[gordo]

I have all the guts from a Maestro Parametric and checked.  Wrong value.  In the 80's when everything HAD to be rack mounted I tossed the enclosure :-(

[Timko]

Yeah I've been down that road before, you'll probably have to keep an eye on ebay for used lots of old potentiometers.

It's not ideal but the rate pot is more dependent on taper than the 'balls' so you could switch those around and try out a standard log or linear for the feedback which are a little easier to find in 24mm.

You can also try and repair the wafer (I know pinkjimiphoton uses a pencil to do it) but perhaps if it had been fiddled with before, that might have already been attempted and failed.

I ended up finding a NOS 1M-C on eBay.  Once it's here I'll attempt to replace the wafer.  It also appears whoever did work on this before I did put in a 3M (idk what taper) pot, so it will be good to restore that to the spec'd value.

[Timko]

Ok, I got this 24mm pot.  How do I replace the wafer?

[Scruffie]

You switch these bits around.

[Timko]

While trying to straighten the pins, i cracked the damn wafer .  Oh well, I'm sure sourcing another 1M-C will be super easy  .

Anyway, I see what to do now.  After taking the wafer off the original pot, it was nearly worn through.  Parts of the left terminal were connected to the middle one too!  I tried cleaning off the original wafer, but there's still places where the connection fails.  I'll start looking for another pot though (perhaps with a different taper) and see what I can find.

[Timko]

It turns out 1M-C pots are easier to find if you search for them in standard (15/16") vs metric (24mm).

I have another one coming.  I broke the last wafer trying to turn some solder lugs into panel mount pins; I'll be considerably more careful this time.

[Timko]

I was able to order another pot, and got the wafer replaced.  I had to create my own panel mount lugs to get it into the existing PCB.  Thanks everyone for the help!

[Scruffie]