Replacing potentiometer inside Brent pedal

[Bill Kielb]

@Brandon B @Dick White @Mark C.

If I go to Mouser electronics and smart filter passive components by: potentiometer, slider,500k&1M I get a boatload of options that can be sized by travel, etc..... I think I would try the 500k and adapt the low and high speed voltage divider if they didn’t have enough range or install a fixed resistor  as needed to limit the current if that was an issue. Seems like the original mounting was a bit aweful, but ..... they worked so I think I could epoxy anything in place with some bracing and make it work as long as relative travel and size were reasonably close.

anyway, if it helps, looks like 500k or 1m available these days:

 

 

Edited January 1, 2021 by Bill Kielb

[Dick White]

3 hours ago, Mark C. said:

Dick whats the amps on that 90v ?

Mark, my bad halfway... looking at the label on mine now, it is 115V DC, not 90, 1/2HP, 5 amps.

[Brandon B]

6 hours ago, Mark C. said:

Brent makes  and did  make 220 wheels they where mostly for export market.

The pot slider also has to have the end connection to work well to attach to base.

I have moused around for hours looking for the Pot sliders with the right lever and mounts-never found one yet.

AH! that makes so much sense. I forgot that the rest of the world uses 220V at their outlets.

[Mark C.]

The pot slider is made by CTS in Taiwan the number on side is 22126. 1846

I have a new one in hand now. CTS is a well known brand

 

This is for the standard Brent foot pedal not the early 70s model 

Bill

maybe your detective work can find this same unit. Its still elusive-the unit is black pastic body with black metal end caps-you bend one into the Brent holder.

[Bill Kielb]

Maybe if you can match the value  or get close it can be a nice project for solidworks and a 3 d printer to make an adapter.

[Brandon B]

On 1/1/2021 at 10:29 AM, Brandon B said:

sorry here it is if you still need it:  (RCV) BX8195-0

https://www.surplussales.com/Potentiometers/Slider/Slider-1.html

 

I just replaced the potentiometer in the pedal with the one from the website above. It was a little tricky.

First, unsolder the old slider, and remove it. 

Second, the slider arm is too fat to fit inside of the metal arm, so I secured it in a vice and used a file to trim the fat off the top and bottom of the slider arm.

Third, the potentiometer's install tab is on the wrong side. I used a 1/4" chisel to pop a small slit in the plastic plate so the tab could go through. Epoxy was my backup plan, but the chisel worked. Then I bent the tab so lock the pot in place on the plastic board.

Fourth, I gently bent the prong to the side so it would touch the connecting wire. I pressed the connecting wires into place that attach the slider pot to the trim pots. The connecting wires are stiff wire, not multi stranded, so you can move them into place and they will stay put. 

Fifth, the connecting wires had enough solder on them to reattach them, but I put a dab of solder on top, just to be sure.

I found when I ran the first test, that I had to really tighten up the Allen set screw on the metal arm, because the old pot is very easy to slide compared to the new one. I reset the trim pots and it works perfectly.

Frankly, I'm surprised at how easy everything went together. I'm sure there are pots that might have the tab on the right side and a skinnier slider arm, but whatever. The wheel moves sooooooooooo beautifully. I've used a bunch of Brents, but I've never seen it ramp up and down so smoothly. I'm happy with the results. 

 

[Bill Kielb]

6 minutes ago, Brandon B said:

y. I'm happy with the results. 

So the 1 megohm pot was the winner! I think if one searches the mouser site and looks through the data sheet and physical properties a close match might be available.

[Hulk]

Thanks for the follow up Brandon B, and good work!

[RobS]

Could a moderator possibly sticky or pin this fix for this old Brent pedal issue to Mark C's Brent wheel fix-it section?  Brandon's solution works, the modification is simple and saved me a hundred bucks plus days of aggravation.  If you can solder and file/cut a little bit of plastic this is an easy fix to replace a part long thought extinct.

 I just acquired a 1975 Brent in excellent shape save the slide pot was shot.  I was about to pull the trigger on the $100 slide pot assembly from Amaco figuring it would fit (it won't I found out after some research) when I decided to see if I could get just the slide potentiometer.  I found this thread, ordered a couple of the 1M pots from the surplus place and had it fixed in probably 1/2 hour.  One thing that made my life easier was to use a Dremel with a small stone to sand the shaft of the slide pot and then switch to a tiny pointed burr to bore an ovalish slot in the opposite end for the mounting tab (which is on the slide side on this particular model).  I was afraid to hit 50 year old bakelite/plastic with anything like a chisel so a Dremel seemed like a good choice.  The new pot sits perfectly in the nest in the pedal casting and cutout in the plastic.  It should last another 50 years, but I have a spare now just in case

For the record, I believe mine is from 1975 as the serial number ends in 75, but here's a picture of the control box for comparison and anyone who may be in the same situation.

Brandon covered this thoroughly, but I'm also happy to share more pictures or descriptions of the modification if it would help folks.  Thanks.

[oldlady]

just found this and though i do not have the problem, i wanted to mention a slight improvement for reading the metal label shown just above.  that is an excellent example of how to photograph that kind of label and is is very clear.    sometimes they are illegible but  if you use a very soft pencil that is not too sharp to run over the numbers, some of the pencil graphite will stay in the numbers and be more easily read.   then the photo is even clearer.

Edited March 20, 2021 by oldlady

[Al Martin]

Any idea if I can do this fix for an older Pacifica GT-400 pedal?  Same problem that pot doesn’t work and can’t get any replacement part info from Pacifica other than their Magic Pedal replacement for a whopping US $350!

[Bill Kielb]

1 hour ago, Al Martin said:

Any idea if I can do this fix for an older Pacifica GT-400 pedal?  Same problem that pot doesn’t work and can’t get any replacement part info from Pacifica other than their Magic Pedal replacement for a whopping US $350!

Picture of it and what is it’s measured value. Most pots can be replaced with a little work.

[RobertCorlett]

What if one were to get carried away and accidentally over-adjust the high trim pot on my brent c pedal? I did that today and heard a snapping sound, loosening a thin circular piece of black plastic from within the trim component. Any idea what to replace it with? Fixed resistor -- if so, what ohm for max power?   New trim component -- if so, can I harvest one from an old marantz stereo? 

[Bill Kielb]

Sounds like you broke the trim pot. What value is it and replace with something close if no exact match is found. Lots of potentiometers available in the electronics world.

Edited June 27, 2022 by Bill Kielb

[RobertCorlett]

Thanks Bill. Research on this forum and an electronics thread suggests a 250k ohm trim potentiometer.  Existing broken one is easy to remove and there is plenty of space to use an alternative trim pot. And I might be in luck -- I have a broken Marantz sd3000 cassette deck and it includes 250k ohm audio tapers. Trying one this afternoon. 

[Bill Kielb]

1 hour ago, RobertCorlett said:

Trying one this afternoon.

Should work, audio taper is logarithmic though so might be touchy. Lots of electronics on the web for same form factor. Check rating first op I believe had a little doubt and never finished drawing. Since then I did find this as a generic Brent motor control.

 

Edited June 28, 2022 by Bill Kielb

[Dave Earley]

I just had a minor flood last week in my garage, ( blocked drain) and my Brent wheel would not stop.  I took the bottom plate off the pedal and saw some moisture.  I blew it dry and tried to adjust it and it wouldn't stop spinning.  Spent hours on line searching for answers, saw high prices. My wheel is a Brent CK (a kit I think) and is at least 50 years old although not used for 3 decades so I was getting resigned to spending $600 to fix it.  I tried adjusting the pedal one more time and it works now. Phew.  It is a great wheel.

[Mark C.]

Dave can you post a few photos of your CK wheel topside and bottom,motor etc

Edited July 27, 2023 by Mark C.

[Dave Earley]

Maybe pictures are here

[Mark C.]

Your CK is looking like a 1/2 hp original brent blue motor . I had that motor on my model C in 1970.

The controller is not the earlier model in a cheaper metal electrical 4 square box so it a bit more modern than the 1969 models.The front is also a give away on the control panel

If the deck is 1/4 steel and weight a ton my guess is this whell is 1974-1976-The other stand out is the more modern foot pedal-they changed to that in 72-73 if I recall 

It has the 12 inch head as well. I wore my bearing out on the head in about 30 years of hard use (full time) swicthed to 14 inch head

[Dave Earley]

Here are the documents that came with the wheel. I don't remember how or where i bought this wheel but I'm sure it was in 1973.

[Mark C.]

I ordered some of these potentiometers as the site has a 25$ min buy (I got some other items as well) if you are needing  one just PM me-they are super low cost