Why when I Replace the PCB pot with manual pots, the manual pots wont work when correctly wired

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Ok I am scratching my head on this and am going mad with this.

As some of you know I am trying to replace 4 Bochen PCB pots with standard manual pots. 2 circuit boards. Please see photo below.

I have tested the boards and they both work fine with the original pots. I use a solder wick and removed the PCB pots on BOTH Boards making careful note of the position of the pot, and numbers on a map of the board as well as the terminal holes 321 CW (they are reverse of a standard pot) I then soldered 22g wire (about 10" long) to the boards where the pots were . I then solder the other end to B series pots with the CORRECT value, connecting wire 1 to terminal 1 2 to terminal 2 and 3 to terminal 3.

Here is the problem When I connect it up, no output voltage is coming ( let me re-phrase the voltage matches the input voltage) I try to turn the Voltage pot up and down and nothing happens, on the LTC3780 buck boost the voltage does not drop or down, on the 1500w the voltage does not increase form the power in of 12v. It can go up to 85volts When I try adjusting the CC the same nothing, and the voltage cut out will not work either

I thought I might have burned out the board, but I thought I'd take a chance, I soldered in the original PCB pots and everything is working fine... WTH is going on???

Please help, I have wired everything in correctly of this I am sure, the #2 wire is the key, IF and this is a big IF (as I have quadrupled check the wires prior to powering up) I flip flopped 1 and 3 it would just change the atunation correct??

This is driving me crazy!!!! I don't get it please help me out...

GS00936-12.jpg LTC3780_WD2002SJ.jpg
 

EM Fields

Joined Jun 8, 2016
583
Ok I am scratching my head on this and am going mad with this.

As some of you know I am trying to replace 4 Bochen PCB pots with standard manual pots. 2 circuit boards. Please see photo below.

I have tested the boards and they both work fine with the original pots. I use a solder wick and removed the PCB pots on BOTH Boards making careful note of the position of the pot, and numbers on a map of the board as well as the terminal holes 321 CW (they are reverse of a standard pot) I then soldered 22g wire (about 10" long) to the boards where the pots were . I then solder the other end to B series pots with the CORRECT value, connecting wire 1 to terminal 1 2 to terminal 2 and 3 to terminal 3.

Here is the problem When I connect it up, no output voltage is coming ( let me re-phrase the voltage matches the input voltage) I try to turn the Voltage pot up and down and nothing happens, on the LTC3780 buck boost the voltage does not drop or down, on the 1500w the voltage does not increase form the power in of 12v. It can go up to 85volts When I try adjusting the CC the same nothing, and the voltage cut out will not work either

I thought I might have burned out the board, but I thought I'd take a chance, I soldered in the original PCB pots and everything is working fine... WTH is going on???

Please help, I have wired everything in correctly of this I am sure, the #2 wire is the key, IF and this is a big IF (as I have quadrupled check the wires prior to powering up) I flip flopped 1 and 3 it would just change the atunation correct??

This is driving me crazy!!!! I don't get it please help me out...

View attachment 129709 View attachment 129710
My guess would be that those 10 inch antennas are doing nasty things to the circuits.
Do you have access to an oscilloscope?
 
i don't have the foggiest what's going on.

let's say you do the following with one pot.

1) Solder three 10" to the new POT.
2) Remove the old POT.
3) Use an ohmmeter to adjust the new pot to the old values.
4) Install the new pot with the same orientation.

Aside.

2 pins would be the value of the pot, e.g. 10K and won't change.
The wiper will vary between the endpoints. e.g. 2K-8K
If you get the endpoints mixed up, increase/decrease will be backwards.

What do the new pots look like?
 

R!f@@

Joined Apr 2, 2009
9,919
If OP is replacing the POT's with long leads that the problem lies in noise pickup.
OP can use shielded wires and try.

Since they are SMPS, the switching frequency could be causing havoc in the long wires
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hey keep it simple, the old pots are like the photo in post 8, the new pots look like these. I am using the B Type pots of appropriate values.

SKU047544_S5.jpg


i don't have the foggiest what's going on.

let's say you do the following with one pot.

1) Solder three 10" to the new POT.
2) Remove the old POT.
3) Use an ohmmeter to adjust the new pot to the old values.
4) Install the new pot with the same orientation.

Aside.

2 pins would be the value of the pot, e.g. 10K and won't change.
The wiper will vary between the endpoints. e.g. 2K-8K
If you get the endpoints mixed up, increase/decrease will be backwards.

What do the new pots look like?
 
Your replacing a 10-20 turn pot with a 270 deg turn pot. The adjustment can be bouncy.

502 and 204 are 5,000 ohm and 20,000 ohm respectively.

504 and 204 are 500K and 200K respectively.

With the new pot oriented shaft toward you and terminals up, the wiper is the center position of the new pot. CW will be the top right terminal.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
What you are saying is that on the blue pot CW = pin 3 left side, and on the new pot with the shaft CW is right, pin 3 Correct?

That is the way I had them hooked up pin 1 on the blue pot to the pin 1 on the new pot and so on... they did not work 321 to 123 wire from pin 1 right to pin 1 left, wire 2 from pin 2 center pin to pin 2 center pin, wire from pine 3 left to right pin 3


Your replacing a 10-20 turn pot with a 270 deg turn pot. The adjustment can be bouncy.

502 and 204 are 5,000 ohm and 20,000 ohm respectively.

504 and 204 are 500K and 200K respectively.

With the new pot oriented shaft toward you and terminals up, the wiper is the center position of the new pot. CW will be the top right terminal.
 
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Thread Starter

born2dive00

Joined Oct 24, 2016
285
I don't know if this is of any importance, when I soldered the wires to the new pots and connected the wires to the corresponding pin hole on the board, and when I tested the new pot with my ohm meter by first checking the over all resistance of pin 1 and 3 then pin 1 and 2 and then pin 2 and 3 there was nothing detected.

As soon as I desoldered the pot with the shaft, there was resistance between the pins again....

Does this help? Is that normal

I checked the resistance on the pins and on the rivits. nothing when wires soldered to the board and the pots, soon as I de solder the pot and it is by itself there is resistance. this has happened to all the pots I have tried, 3 different pots for each of the blue pots.
 
that new POT is 500K, BUT it could be linear or LOG taper. A LOG taper could really mess things up.

So, take your new POT and measure the resistance from end to end - You should get 500K or something close.

Now, the hard part. Rotate the pot until it's midway. Now check for 250K and 250K - wiper to each end.
If you get 10K, 400K or something similar when it's CENTERED then we have an oops. You have an Audio taper.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
KISS, isn't a log pot identified as an A type pot? i.e. A500K and a linear pot identified as a B500k?

I will try it when I get home from work and let you know.

that new POT is 500K, BUT it could be linear or LOG taper. A LOG taper could really mess things up.

So, take your new POT and measure the resistance from end to end - You should get 500K or something close.

Now, the hard part. Rotate the pot until it's midway. Now check for 250K and 250K - wiper to each end.
If you get 10K, 400K or something similar when it's CENTERED then we have an oops. You have an Audio taper.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hello every one Here is a photo of my setup
Using servo leads, the pcb servos work in both locations as seen below in photo 1.

Thinking it was an issue with cheap pots I bought Cosmos Tokyo pots which most expensive pots highest quality pots I can get. I replaced the 204 PCB pot with a cosmos B 204 pot I set the value to the same as the pcb pot and wired it up to the CV pot pin 1 on the board to pin 1 on the pot, pin 2 on the board to pin 2 on the pot, pin 3 on the board to pin 3 on the pot. I plugged it in, and NOTHING (just the default voltage of 11.97v which is the same voltage as the power supply.

WHAT THE ^&$£*()(&&^)*((&*^$"$%$ is going on????? I am ready to fix this with a flipping shot gun!!! Please help I am pulling what little hair I have out of my head!!!!


P_20170626_212132.jpg

Here is the notes on the board that I have discovered
GS00936-12.jpg

Please help I am loosing my mind!!
 
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Thread Starter

born2dive00

Joined Oct 24, 2016
285
Please see the photo above of the setup, using servo wires and the original pots the system works fine, as soon as I solder ANY external
pot to it, it defaults to the default voltage of 11.97v so I dont think it is the servo wires that are the problem. these servo wires are 40cm long

Make the connections to your new pots as short as possible and report back.
Make the connections to your new pots as short as possible and report back.
 

R!f@@

Joined Apr 2, 2009
9,919
I'm confused a bit.
Can you post the numbers on the multiturn trip pots that is originally on the boards.
Together with the number that you are replacing them with.

There must be an error that you doing, I am not sure.

If the resistance match.
try replacing the voltage pot first. Keep the other trimpot ( original ) soldered on the PCB as it were before.
First try using shorter leads.
If it works try the longer leads.
 
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