Help fixing three FC-7 footpedals!

[RandyFF]

I have very limited experience with electronics, but this should be a simple fix. AFAIK, the only 2 things that can wrong is the cable and the potentiometer.

 

I changed out the cable on one of these 3, using a high quality cable and a Neutrik TRS right angle plug. My repair worked, but in less than a year it stopped working.

 

Yesterday I did a continuity test on all 3 pedals from the plug to the 3 prongs of the potentiometer. All 3 of the pedals have a continuous circuit from the 3 prongs of the pot to the tip/ring/sleeve of the plug. HOWEVER, the one that I'd changed out the cable and plug, the middle prong of the pot has a continuous signal to the ring AND the sleeve.

 

Do potentiometers go bad? What else could be going on?

 

Having done a visual inspection of the solder joints I'd done on the one I changed out, I'd guess my soldering joints are in good shape, and the continuity test seems to confirm that. But why would the middle terminal of the 3 pronged pot be sending signal out to both the tip and the sleeve?

 

Input very much appreciated!!!! Would rather not throw away $150 worth of pedals 'cause I'm lacking technical know-how.

[Baldwin Funster]

I dont know specifically about those pedals but yes a potentiometer can go bad. Especially ones from a certain country known for cheap electronics who I wont name .

[Markyboard]

Hi Randy-

 

Snap a picture and then remove (yes - unsolder) the cable completely from the potentiometer. Turn (or pedal) the pot to one extreme (max or min) and test continuity from wiper (middle terminal) to each of the other terminals. One side should be open and the other shorted. Then turn the pot to the other extreme and repeat the continuity test. The results should be opposite of the first test.

 

Btw an Ohm meter would be much more revealing if you can get hold of one.

 

Let us know what happens.

[RandyFF]

Hi Randy-

 

Snap a picture and then remove (yes - unsolder) the cable completely from the potentiometer. Turn (or pedal) the pot to one extreme (max or min) and test continuity from wiper (middle terminal) to each of the other terminals. One side should be open and the other shorted. Then turn the pot to the other extreme and repeat the continuity test. The results should be opposite of the first test.

 

Btw an Ohm meter would be much more revealing if you can get hold of one.

 

Let us know what happens.

Exclnt! Will do.

 

I do have a good MM, but I barely use its capabilites. I use it mostly for continuity and battery voltage tests.

 

BK Tool Kit 2704A multi-meter

 

At the moment I have the black probe connected to the COM port, and the red probe connected to the VOhm port (Ohm written just as the symbol).

 

Thanks,

Randy

[BluesKeys]

I am following this thread because I have an FC-7 that I need a potentiometer for! Where can I source one?

[Markyboard]

I am following this thread because I have an FC-7 that I need a potentiometer for! Where can I source one?

 

Hey Jimmy-

 

Your best bet is to contact Yamaha service. Per forum member OB Dave the pot is custom as discussed here.

[RandyFF]

Markyboard,

As you can see, my MM is an Ohm meter as well.

 

I did the test you described, and it behaved like you said it would. Does that mean this pot is OK?

 

It's an Alps pot, japan, the markings on the side read

1. 517G / 50KB. This is the one I replaced the cord and plug on

2. 716G / 50KB

3. 517G / 50KB

Yes, these are well-made and designed pedals, don't know why I've had 3 failures!

 

I also tested another one of the 3 with the test you described, but didn't unsolder the wires from the pot. Same results.

 

Thanks again for the help!

[Markyboard]

Hey Randy-

 

Since you have a "real" Ohm meter the next step would be turning the pot from min to max ( and max to min) several times slow and fast observing the resistance increases/decreases smooth from near 0 to near 50 Ohms. Btw if you read the link I provided for Jimmy above OB Dave discovered that the pot is indeed Alps, custom made for Yamaha. The sweeping has to to be done while the pot is mounted in it's housing that intentionally provides physical limits/constraints near each extreme. If all looks good then yes, the pot is good and it's a bad cable.

 

I suspect that the pedal you claimed failed which looked good with cable attached may be an intermittent cable short or open. Maybe try it again while really jostling that cable and see if your Ohm meter changes abruptly while doing so. I think most of these problems are due to bad cables. If you're somewhat industrious you can do what Escape Rocks (aka David) posted about a while back which is to install a 1/4" female jack. I've done this on all 7 of my FC-7s (some prior to David's post )and about to do 2 more that I acquired yesterday (thanks Griswold).

 

If you're interested in this I can provide pics and instructions. Having a removable quality cable is so worth the 15-45 minute effort.

[RandyFF]

Markyboard,

Cool, I'll do the Ohm meter sweep.

 

Yes please, AFAIK most pedal failures are because of the cable, so installing a jack on the pedal makes a lot of sense!

[Markyboard]

Apologies if this duplicates a previous post by Escape Rocks. I just finished modifying 2 recently acquired FC-7s and cabling them into my setup so...

 

The audio jack you want is a Switchcraft L12B (or L-12B as some list it). Make sure you get the 'L' version as this has the Longer barrel which you need for the FC-7. My last order came from Newark Electronics. Many music retailers carry them as well so if you intend to bundle it with anything else perhaps you save on the shipping cost.

 

Drilling: This is without doubt the hardest part - and not all that hard. I use a 13/32 drill bit. You can mount the jack on either side of the internal cable strain relief structure. I always use 'pedal left' (for some reason). Target the hole just a hair north of vertical center and you should be fine. Too low and the connector won't go in straight. It's wider at the back of the connector and you'll end up having to widen the top of the hole (not a big deal). Too high and you end up with an opening at the top. Not the end of the world as I found out on one of the 2 I did yesterday. Apparently my cheapo drill bit didn't quite grab in the intended spot and so the hole got a bit mangled with the top "open". The connector still fits and tightens securely but this one's not winning any prizes. I recommend (now) a much smaller drill bit to start and then widening it with the 5/32 bit.

 

 

 

Insert the connector with the provided washer on the outside. Turn it so the solder contacts are facing up. Tighten the nut.

 

 

 

 

The rest is really easy assuming you can do basic soldering. Cut most of the cable leaving maybe 6 inches or so on the outside and then pull that remaining portion through to the inside of the pedal.

 

 

Strip and solder red to ring and white to the tip for Yamaha/Korg type boards, and vice versa for Roland and similar. Braid of course to the sleeve (center terminal). Note the tip/ring solder terminals are opposite of the actual tip and ring contacts. If in doubt use a meter. This one is wired Yamaha/Korg.

 

 

I wrap the excess cable as shown, it stays in place and doesn't get in the way. Should I need to redo it, or change the phase I have plenty to work with without having to open the guts of the pedal mechanism.

The nice thing with this is if you ever need to change the polarity it's really easy to swap the wires going to the tip and ring of the new jack. At one time I was going to add a switch but I just don't have the need.

 

That's it - let me know if you have any questions.