dasatcopthorne Posted January 19, 2016 Share Posted January 19, 2016 Hi Guys. An accident when exhibiting at the St Albans show last weekend has rendered one of our Kent Panel Controllers useless. It fell into the floor. It's a 3amp Heavy Duty version I have checked what I can with the wiring etc but electronic circuits are a mystery to me. However I found that the main control knob was broken and 99% probably the cause or one of them. I feel confident on the actual replacement but not about the component. The pictures show the pot in detail. It's legs were soldered direct the the circuit board so when the board is removed the pot comes with it. I plan to fix the new one just to the controller body then 'wire' the pot to the correct points on the board with 6" leads. My query is the component description. It reads 4k7. I know this 47000 ohms but 'LIN.A' is new to me. The pot has three 'legs' soldered to the board and all seem to be used. I opened the pot to find two black tracks with wipers. Are these Carbon? Any help much appreciated so I can buy and fit a replacement. Dave Carshalton & Sutton MRC Link to post Share on other sites More sharing options...
smokebox Posted January 19, 2016 Share Posted January 19, 2016 LIN means linear. The alternative would have been LOG, meaning logarithmic. It describes the way the resistance increases and decreases as the knob is rotated. Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted January 19, 2016 RMweb Premium Share Posted January 19, 2016 Dave, 4k7 is 4,700 ohms not 47,000 (was that a typo), yes I agree it would be linear. Link to post Share on other sites More sharing options...
dasatcopthorne Posted January 19, 2016 Author Share Posted January 19, 2016 Thanks Guys. Yes a typo there.. Cheers Dave Link to post Share on other sites More sharing options...
dasatcopthorne Posted January 19, 2016 Author Share Posted January 19, 2016 Thanks very much guys. New Pot obtained and replaced. Controller working again. Cheers Dave Link to post Share on other sites More sharing options...
dasatcopthorne Posted January 27, 2016 Author Share Posted January 27, 2016 Thanks agian for the help in replacing the pot on our controller. Now, another problem. Possibly because of a slight rise in the input ac voltage, this controller will no longer completely shut down, always leaving a small voltage on the track. (New transformers fitted to power supply that may be more efficient) To start with, does anyone, please, have or know of, a circuit diagram for the Kent Panel Controls (KPC) hand held controller. This one has switchable feedback. Cheers Dave Link to post Share on other sites More sharing options...
Gordon H Posted January 27, 2016 Share Posted January 27, 2016 As you have one, why not do a bit of reverse engineering to produce a diagram yourself? Chances are the most you might have to do to correct the problem is add a padding resistor to the top of the pot - or perhaps remove one at the bottom, if one exists? Should become apparent once you have produced the diagram as to what remedy to adopt. Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted January 28, 2016 RMweb Premium Share Posted January 28, 2016 Dave, Do you know what the small pot by the switch is for? Could be a zero adjust. Link to post Share on other sites More sharing options...
dasatcopthorne Posted January 28, 2016 Author Share Posted January 28, 2016 Dave, Do you know what the small pot by the switch is for? Could be a zero adjust. David. I had considered this but to be honest, I'm frightened to alter it in case I cannot get it back exactly to where it was set. On the top end of the pot there is a 47k ohm resistor but none on the bottom end. The output shows there is .04 volts present all the time. I am thinking that fitting a resistor here might cure it. Sorry, but reverse engineering is too complicated for me. Dave Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted January 28, 2016 RMweb Premium Share Posted January 28, 2016 I do not think a resistor at the bottom will help, it might make the off voltage higher. You can always try a small value and see what happens. Slim chance, but do you still have the old pot? There may be a clue if there is a difference in value, pots are not renowned for being close tolerance. Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted January 28, 2016 RMweb Premium Share Posted January 28, 2016 Did you find these people, do they still exist? http://www.locomotive-model-shop.co.uk/kp-tech/HTML/index-2.html Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted January 30, 2016 RMweb Premium Share Posted January 30, 2016 David. I had considered this but to be honest, I'm frightened to alter it in case I cannot get it back exactly to where it was set. On the top end of the pot there is a 47k ohm resistor but none on the bottom end. The output shows there is .04 volts present all the time. I am thinking that fitting a resistor here might cure it. Sorry, but reverse engineering is too complicated for me. Dave Not sure that 0.04 of a volt is going to make any difference. What happens if you put a loco on the track & leave it. Does it move or make a buzzing sound? Did you measure the output voltage of the old one, before it died. It quite likely 'leaked' too. That is tolerance problem in the pot. Link to post Share on other sites More sharing options...
DCB Posted January 31, 2016 Share Posted January 31, 2016 As Kevinlms says put a loco on the track, run it up and down, stop it and then check the voltage across the track. My guess is it will be way down in the 0.004volt range, and absolutely normal. The pot's max resistance is 4.7Kohms (not infinity) so it will leak unless it is a specialist pot with a dedicated off position, normally a click. When you get away from the old Hornby Dublo controllers with a knob you turn left for reverse and right for forward most controllers "Leak" which is why they should not be left switched on for weeks at a time. Link to post Share on other sites More sharing options...
Gordon H Posted February 1, 2016 Share Posted February 1, 2016 The pot's max resistance is 4.7Kohms (not infinity) so it will leak unless it is a specialist pot with a dedicated off position, normally a click. When you get away from the old Hornby Dublo controllers with a knob you turn left for reverse and right for forward most controllers "Leak" which is why they should not be left switched on for weeks at a time. The pot's actual track resistance ought to be largely irrelevant, as in most designs the control would be being used as a pot rather than a variable resistor. How well a controller works at low settings is down to the overall design, not specifically a fault of the pot. Certainly, any perceived output 'leakage' should be assessed with a load on the output (i.e. a loco on the track), otherwise you could easily be misled into thinking something was wrong. Link to post Share on other sites More sharing options...
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