PCM70 Input Pot Replacement Help. Picture inside of broken Pot

[tubejay]

I just received this PCM70 and it was packaged well, but the box was WAY too small and the input knob was up against the side.  It must have taken a small hit and shipping and broke the input knob (see pics).

Does anyone know which Pot to get and where to get it?  I'm terrible at figuring out which pot to buy in these situations, plus it's got an odd way of holding it in place.  Any help here would be great.  Obviously it's not working right now because there's no signal getting to the reverb, or to the outputs.  I'm pretty sure it'll work just fine if I replace the knob.

The knob reads "8728h" and "10kd" across the top.  Whenever I order these things I seem to order the wrong size/shape etc, so any help would be greatly appreciated in finding just the right one, or at least one that I can work in there and have it be solidly in there.

Thanks,

Jay

 

[tubejay]

I took the potentiometer out and took some more pics.  I spent the afternoon perusing Mouser and Digikey, but I really...really suck at sourcing parts.  Does anyone know if it's a log or lin pot?  Anyone have the schematic?  Worse comes to worse, I guess I'll run down to radio shack and see if someone there can help me, but I'd really hate to buy one of their shitty pots.

Anyways, here's the pics, any help would be GREATLY appreciated.

 

[MartyMart]

http://answers.google.com/answers/threadview?id=335708

I found some "D" taper sliders for a mixer but the above answer states that
neither the old nor new pot designations used the suffix "D" as an indication of a taper.

Not much help I know, but I least I looked around for several minutes !
I would guess linear and in general if you don't know for sure, at least that would work with a 10k B
99% of the time. ( if in doubt I use a linear taper )
It does look like a fairly cheap generic pot and I have ones that look similar taken from
some old Japanese guitar pedal.
If you can find a similar size pot you can prize away the housing and probably re-shape
and re-use it.
I'm sure that the audio doesn't pass through that, it will be just a control voltage pot as in the
50k's on the GSSL.

MM

 

[sahib]

Just use your multimeter to figure out.

Open it up.

Place one probe in the middle of the track and measure both ends. If it is a standard log pot, one side will read about 1k while the other 9K.

 

[Joechris]

Why do you need a pot? Replace it with a link and a 10k.

 

[tubejay]

So what do you think of this one?

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P3R7103-ND

It's a 10k Linear and it looks like it's very similar as far as the pins and the way it's designed to mount to a pcb.  I'm not sure if it's the right size though.  Is there any red flags with this one?  Again, I'm pretty terrible at ordering this stuff, and I'm not as well versed in this stuff as everyone who posted in the thread so far.  ;D

Thank you very much for the replies thus far. 

Anyone have a schematic for the PCM70?

 

[kazper]

A pair of calipers (Harbor Freight has a digital pair for $15) will help you figure out shaft bushing diameter and PC Board pin spacings. A non standard ruler with 32nd of a inch will also help, but you would also have a caliper if you had that.

These also work good on layouts of front panels, figuring out what type of headers to use, Capacitor leg spacings for PCB's... on and on...

Generic picture but it looks like you can see what that pot's configuration was etc. with a voltmeter on Ohms measurement.

Place the leads on the carbon traces and turn the pot from left to right with it connected best you can do. Try to look at the positions in 25% increments and then post what you have.

It could be one of many different types of curves. Maybe your lucky and it's a plain jane lin pot.

 

[kazper]

Like it was said by joechris, you could getaway with just a resistor for the time-being once you take that pot apart and figure-out how it worked in the circuit.

It also looks like if it's a standard pot a generic Alpha pot would fit and you could probably modify it to have the supports. If it uses the nut, I wouldn't worry about it.

 

[SSLtech]

It's log.

It's 10kΩ, single-gang apparently.

You can strap the center pin with the clockwise and have it work. -For DC reference, a 10kΩ resistor to the counter-clockwise end might not hurt.

But you should be able to find something that will fit in there. -Check a local surplus shop.

Keith

 

[tubejay]

It's log.

It's 10kΩ, single-gang apparently.

You can strap the center pin with the clockwise and have it work. -For DC reference, a 10kΩ resistor to the counter-clockwise end might not hurt.

But you should be able to find something that will fit in there. -Check a local surplus shop.

Keith

Oh how I wish we had a surplus store near me.  The nearest one I know of is in Madison, WI, and that's over 2 hours away. 

Thanks for the info Keith, I don't even know how many times you've helped me out on this board, but it's been a lot.  I really appreciate it.

After some lousy measurements with my crap ruler, I think this one will be workable. 

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P3S8103-ND

It's 10k Log with slated shaft, single gang.  It looks like it might, possibly, even drop right in, but I think it's a hair too short for that.  I figure if the shaft is too long I can just clip it off. 

The only thing that worries me about not having it solder to the main PCB is that the part the nut screws on to is the same flimsy PCB that the display is on.  So a strong bump might crack that PCB.  I suppose I could solder some things together and lengthen those legs and that might shore it up. 

Is that resistor business that you mentioned necessary, or is it to improve it?  Or am I compensating for the new pot in some way?  Just curious.

Thanks again!  And thanks to everyone else that replied too.  I know I should get some calipers, but it's one of those things I keep putting off.

Jay

 

[kazper]

look at these options also... since I don't have your measurements it's just a guess

Mouser 317-2091F-10K
http://www.mouser.com/catalog/637/674.pdf (upper right)

Mouser 313-1285F-10K
http://www.mouser.com/catalog/637/675.pdf (bottom of page)

There is a few options here on this page. You may be able to disassemble the broken pot and remove the mounting piece and attach it to the common alpha pots. This would still protect you from the pcb mount your worried about.

http://www.mouser.com/catalog/637/676.pdf

 

[jwhmca]

Have you called Lexicon...? I have repaired many, many of these types of problems... I usually find that the original part is cheap and available from the manufacture of the device...

  I once had a dbx, with all the controls broken (yep, all) Mouser wanted $3.5 for the alpha controls... dbx had them for $1 each. I have also had companys send me parts for free... It seems sometimes they feel they should have built them better???

Anyway, give it a try!

 

[tubejay]

Thanks Kazper, I'll check those out. 

And yes, I've checked with Lexicon, and they like to pretend that their most beloved and famous studio equipment never existed.  Unfortunately that includes the PCM70, which they say they don't even have one at their office anymore, let alone any parts.  :'(

 

[tubejay]

Mouser 313-1285F-10K
http://www.mouser.com/catalog/637/675.pdf (bottom of page)

The 675 looks like it'd fit well, but unfortunately it doesn't have the threads to put a nut on there.

 

[tubejay]

After some lousy measurements with my crap ruler, I think this one will be workable. 

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P3S8103-ND

It's 10k Log with slated shaft, single gang.  It looks like it might, possibly, even drop right in, but I think it's a hair too short for that.  I figure if the shaft is too long I can just clip it off. 

I just wanted to report back that this is a good replacement.  I put it in, works great.  I had to bend the pins and then they just sat on the holes, and I was able to solder them into place without adding any extensions or anything else.  The only minor thing with the pot is that it has a detent in the top middle, which actually is kind of nice.  So it works great!  Thanks again for all the help, and thanks for steering me in the right direction Keith.

 

[bittalight]

In case someone stumbles upon the need for a replacement pot for either the PCM 60 or 70, the input control, the direct current ALPS drop-in part number is: RK1631110TT3

You will have to use the old mounting bracket or just install the pot as I did without. It has plenty of support with the panel mount nut.

 

[Hmaringer]

In case someone stumbles upon the need for a replacement pot for either the PCM 60 or 70, the input control, the direct current ALPS drop-in part number is: RK1631110TT3

You will have to use the old mounting bracket or just install the pot as I did without. It has plenty of support with the panel mount nut.

Resurrecting this so no one else wastes their time! This does not work on my pcm70. When I installed this pot on my PCM70 it showed input volume at all times and causes the entire unit not to work.

EVU-E3JFK4D14 is also no longer made... So am I SOL or what?