Industrial joystick repair challenge, tips needed. - Page 1
Forum section: electronics / repair

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 12:04:00 am
content: Got an industrial joystick that is defective.The joystick was replaced with a new one, so this joystick has a fault.Testing the joystick by applying 12VDC to the terminals J1, J5Measuring the output, terminal J3 with a Fluke, no load, with the following result:Joystick in neutral = 6,0V OKJoystick full forward = 9,0V OKJoystick full backward = 3,0V OKAdding a load to the output with an resistor 1,2K between J3 and power supply ground.resistor draws 4,9 mA on 6Vnew measure in circuit and output J3, new values indicated in (). See included drawing.Joystick in neutral = 4,25 VJoystick full forward = 4,25 VJoystick full backward = 3,0 VIs it correct/OK to test this way?I have replaced LM258, LM317LM and relay, any idea what can be wrong?Drawing is reverse engineered by me, with hopefully no faults.Resistors are measured on PCB.Capacitors not tested.All diodes tested.Any tips highly appreciated!

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 03:24:35 am
content: Try measuring the 200ohm[located on plate?] value or bypass it with another resistor.

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 10:48:34 am
content: The resistors on the Ceramic slider plate seems OK.Armadillo: Shorted out the 200 ohm resistor with 100 ohm resistor, sorry to say no difference.

author: stj
author_rank: Super Contributor
timestamp: June 12, 2017, 11:45:36 am
content: you arent supposed to put a load on such things.it's junk btw, if you need industrial reliability then non-contact sensing is the way to do it.usually using linear hall effect sensors and x&y magnets.

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 11:54:44 am
content: Quote from: tru3533 on June 12, 2017, 10:48:34 amNow how did you bypass the 200 ohm resistor?Please plug in the module, measure the ohm from Pin 4 of LM258 to anode of D5. What is the ohm?

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 01:08:41 pm
content: Resistor was bypassed by soldering a 100 ohm resistor over pin 2 and 3 on the ceramic slider plate. (counting from left)Notice that the ground level is not changed when applying load.measure the ohm from Pin 4 of LM258 to anode of D5. What is the ohm? 800 ohmK1 coil measure is 500 ohm.

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 01:42:48 pm
content: Quote from: tru3533 on June 12, 2017, 01:08:41 pmHi, your pin 4 is the Actual Ground for LM258, elevated by relay ohm and the 200 ohm. So when you say you put 1.2K resistor at J3 to ground, what ground are you using, cannot use power supply ground? The elevated ground itself drop somewhere 3v.And if coil is 500 ohm, why you measure 800 ohm [ 500 + 200 = 700] or [500 + 200||100] = 566.67 ohm]. Not that I am petty, but I suspect some poor connection, dry joints of the power to the IC.Please also check your 12v power supply by putting some load to it. Test it to write off the suspect for the power supply first to reduce complexity.If you are able, change the LM258, start over measurement using pin 4 as ground.Oh yeah, while you at it with the load, measure pin8 to pin4 of LM258. We see why voltage drop so much.

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 02:46:22 pm
content: Actual ground for LM258 pin 4 is anode D1,D3 elevated by the RSlider 200 ohm.Actual ground for LM317LM pin 4 is anode D1,D3 elevated by the K1 500 ohm + R15 100 ohmLM317LM is not powering the circuit, only function is to supply stable power for feedback of potmeterMeasuring pin 4 LM317LM to pin 4 LM258K1=500 ohm + R15 100 ohm + RSlider 200 ohm =800 ohmAs you see ground levels is not the same.I'm using my trusted old HP lab supply for this measurement, so supply is OKBridge D1,D2,D3,D4 makes the plug to the joystick reversible when you power up the joystick.Ground level will always be D1,D3 anode.Power + level is always D2,D4 cathode.On drawing you see Power+ level = 11,77 V. (12V supply - D2 drop) = pin 8 LM258No drop on power levelLM258 is changed.Resistors R10, R11 is removed from circuit, and measured = 2,5K each

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 04:05:34 pm
content: I relook the circuit, the ground should be marked in Red to Pin 4.Measure all from Pin 4.From Pin 4 to Anode of diode D1, you should actually only read 200 ohms not 800 ohms.

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 04:16:51 pm
content: Quote from: tru3533 on June 12, 2017, 02:46:22 pmno change because you measured wrong ground away from the suspected resistor.Measure Pin 4 to Pin 8, very specific.Measure ohm from Pin 4 to Anode of D1, cannot be larger than 200 ohms, very specific.

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 04:18:10 pm
content: This is correctYour question was "measure the ohm from Pin 4 of LM258 to anode of D5".So I guess this was an typing error.

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 04:23:04 pm
content: I made new drawing to simplify the problem.Looking only at DC level

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 04:33:47 pm
content: The challenge is not the circuit.

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 04:46:03 pm
content: Interesting...But this level on pin 4 is not available on the plug for the joystick.So how is it possible that the joystick can send out the correct value? and be read by the controller?I know for a fact that the joystick is defective.It has been replaced by a new joystick and then everything works.

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 06:04:56 pm
content: Well back to the drawing board :-)I think it is possible to connect the load resistor as I did.I just watched EEVblog #600 - OpAmps Tutorial - What is an Operational Amplifier?Here Dave demonstrate LM358 who is in the same group as LM258The reason why pin 4 is lifted can be seen at @43:22

author: Armadillo
author_rank: Super Contributor
timestamp: June 12, 2017, 06:32:06 pm
content: You are confused with the virtual"INPUT"ground and the power ground."NO VOLTAGE CAN BE LESSER THAN THE VOLTAGE APPLIED AT THE GND PIN"Specifically for LM258, no voltage can be lower than Pin 4.

author: tru3533
author_rank: Regular Contributor
timestamp: June 12, 2017, 10:56:14 pm
content: OK, understand. Thank you for holding outSo the big question is now how can I test the joystick measuring only on the terminal connector?By measuring only with Fluke it seems OK. But it is broken.

author: Armadillo
author_rank: Super Contributor
timestamp: June 13, 2017, 02:59:40 am
content: Try focusing on somewhere else, for example the jack connector, mechanical side mating, could those be loose, wire ends etc....You have 2 of them, can make the comparison. Try plugging it in to see any loose contacts or something like that.I am sure you can find it out. Good Luck with the repair.

author: tru3533
author_rank: Regular Contributor
timestamp: June 14, 2017, 12:12:27 am
content: Found the obvious solution, the circuit works with mA.with reference to ground.The joystick circuit is constructed so it gives out 0 mA in center position and 20 mA range in each direction.Failure was misalignment, with overshooting on the positive side.Took some time, but all in all learned something.