# Smartkit 1138 0-30V 3A Power Supply Troubleshooting

#### kenyon.pat

Joined Nov 18, 2009
20
Hello Audioguruagain
Thank you for that information.
Is there any other op amp that could be used in place of the TLE2141 in your circuit?
Regards Patrick

#### Audioguru again

Joined Oct 21, 2019
5,577
Digikey in North America has 32000 opamps listed with many specification choices. Good luck finding a match to a TLE2141 that is available for you.

#### kenyon.pat

Joined Nov 18, 2009
20
Hi AlbertHall,
All capacitors have been tested and checked. I have changed C1 from 3300uf 50volt to 10000uf 60 volt as a precaution. There is no short across D11. I have removed D11 from the board and tested it again.
I will measure the voltage across R7 shortly and report back. R7 and R3 are getting very hot.
Thanks again for showing an interest in my problem.
Regards Patrick
Hello AlbertHall,
Voltage across R7 = 15.4 volts and minus 27.5 volts. This is with the pots centered as you asked previously. Is that how you wanted it?
Thanks again
Regards Patrick

#### kenyon.pat

Joined Nov 18, 2009
20
Digikey in North America has 32000 opamps listed with many specification choices. Good luck finding a match to a TLE2141 that is available for you.
Hello Audioguruagain,
Thank you for the information.
I do not know how to decide on a good match for the TLE2141 so I will call my daughter in Scotland and see if she can pick them up for me.
I really appreciate all of your assistance.
Regards Patrick

#### AlbertHall

Joined Jun 4, 2014
12,202
Hello AlbertHall,
Voltage across R7 = 15.4 volts and minus 27.5 volts. This is with the pots centered as you asked previously. Is that how you wanted it?
Thanks again
Regards Patrick
I do not understand these readings.
Is this the voltages you read on the leads of R7 with the balck meter probe on the negative output?

Is the current limit LED lit?

#### kenyon.pat

Joined Nov 18, 2009
20
I do not understand these readings.
Is this the voltages you read on the leads of R7 with the balck meter probe on the negative output?

Is the current limit LED lit?
Hello Albert hall,
Red meter lead on the positive output and the black negative lead on the resistor. I have measured on both ends of the resistor. Is this wrong? Would you like me to do it again with the negative meter lead on the negative output?
Regards Patrick

#### AlbertHall

Joined Jun 4, 2014
12,202
That makes the voltage between the ends of R7 42.9V (15.4 + 27.5).
If R7 is the correct value, 0.47Ω then the current would be well over 80A and I don't think that is happening.

My first thought is that R7 is open circuit but you say it is getting hot? Open circuit resistors don't get hot.
a) Put one meter lead on one end of R7 and the other meter lead on its other end.
b) Check that R7 is somewhere around half an Ohm.

#### Audioguru again

Joined Oct 21, 2019
5,577
When the current in R7 becomes 3A (the max output from this project) then it has 0.47 ohms x 3A= 1.41V across it which is fed to the inputs of opamp U3 which causes the output voltage to drop enough to limit the current to 3A.

#### kenyon.pat

Joined Nov 18, 2009
20
That makes the voltage between the ends of R7 42.9V (15.4 + 27.5).
If R7 is the correct value, 0.47Ω then the current would be well over 80A and I don't think that is happening.

My first thought is that R7 is open circuit but you say it is getting hot? Open circuit resistors don't get hot.
a) Put one meter lead on one end of R7 and the other meter lead on its other end.
b) Check that R7 is somewhere around half an Ohm.
Hello Albert Hall,
I will do that and report back shortly.
Thank you
Regards Patrick

#### kenyon.pat

Joined Nov 18, 2009
20
Hello Albert Hall,
I will do that and report back shortly.
Thank you
Regards Patrick
Hello AlbertHall,
I have tested R7 as you asked.
I have a good quality DMM and it measures 0.494 ohms across the resistor.
Hope that helps.
Regards Patrick

#### MrChips

Joined Oct 2, 2009
28,136
Voltage across R7 is 27.5 - 15.4 = 12.1V ?

#### AlbertHall

Joined Jun 4, 2014
12,202
Hello AlbertHall,
I have tested R7 as you asked.
I have a good quality DMM and it measures 0.494 ohms across the resistor.
Hope that helps.
Regards Patrick
Put one meter lead on one end of R7 and the other meter lead on its other end. Please report the voltage.

#### Audioguru again

Joined Oct 21, 2019
5,577
When load current in R7 reaches 3A (the max current for this project) then R7 has only 1.14V across it.
The defective power rating of the original R7 was 5W (then it heats with 3A x 1.41V= 4.23W making it VERY hot) so I increased its power rating to 10W.

#### Audioguru again

Joined Oct 21, 2019
5,577
A good quality DMM has leads that measure about 0.2 ohms causing a low resistance to measure 0.2 ohms too high.
Some DMMs allow you to cancel the resistance of the leads for an accurate measurement of the resistance being tested.

#### kenyon.pat

Joined Nov 18, 2009
20
A good quality DMM has leads that measure about 0.2 ohms causing a low resistance to measure 0.2 ohms too high.
Some DMMs allow you to cancel the resistance of the leads for an accurate measurement of the resistance being tested.
Hello Audioguruagain,
I am using a fairly new Fluke117
I do not see a way of cancelling the resistance of the leads but it does seem to give an accurate reading on the Ohms scale.
Regards Patrick

#### Audioguru again

Joined Oct 21, 2019
5,577
The leads in my Fluke 79III meter measure 2.0 ohms on the auto-ranging scale. Then a 0.47 ohms resistor measures 0.47 + 2.0= 2.47 ohms. My meter and its worn-out leads are 29 years old. Your leads might be newer and measure much less.

On the 40 ohms setting, the leads are shorted together and the "range" button is pressed for a moment then "CAL" is shown which cancels the leads measurement to zero ohms during that one test.

#### kenyon.pat

Joined Nov 18, 2009
20
The leads in my Fluke 79III meter measure 2.0 ohms on the auto-ranging scale. Then a 0.47 ohms resistor measures 0.47 + 2.0= 2.47 ohms. My meter and its worn-out leads are 29 years old. Your leads might be newer and measure much less.

On the 40 ohms setting, the leads are shorted together and the "range" button is pressed for a moment then "CAL" is shown which cancels the leads measurement to zero ohms during that one test.
Hello Audioguru again.
My Fluke 117 is a very basic unit compared to yours. It is primarily aimed at electricians so it falls short in many areas when it comes to electronics. It is auto ranging on the ohms setting so there is no manual setting for different ranges and it will measure from 0.1 ohms to 40 meg. It is only 2 years old and it was given to me by my daughter as a Christmas present. For years I have used the best Major Tech DMM and I was really happy with it until it finally failed and the local agents said it was not repairable. I happened to mention at a family dinner one evening that in the new year I was going to treat myself to a Fluke and before the new year arrived the Fluke 117 arrived. It would have been suicide to go and buy another one so this is what I have and I will make the best of it. Hope you don't mind my long drawn out DMM tale
Regards Patrick

#### Audioguru again

Joined Oct 21, 2019
5,577
When I bought my expensive Fluke DMM my boss said it was too expensive then he bought a Radio Shack simple meter that had only basic functions but it costed much less than my Fluke. His cheap meter failed in a few days and the store had none remaining to give as a replacement. My Fluke meter costed me less than $0.72 per month and still works fine after 29 years. Thread Starter #### kenyon.pat Joined Nov 18, 2009 20 When I bought my expensive Fluke DMM my boss said it was too expensive then he bought a Radio Shack simple meter that had only basic functions but it costed much less than my Fluke. His cheap meter failed in a few days and the store had none remaining to give as a replacement. My Fluke meter costed me less than$0.72 per month and still works fine after 29 years.
Hello Audioguruagain,
Yes, there is no substitute for the best. I was going to buy the best Fluke that I could afford but alas life's little skew balls.
Update on my power supply.
When I first damaged my power supply and didn't know what was wrong I removed and tested all 4 transistors and found 2 that were damaged so I replaces them. After fiddling with other bits I again tried the supply and - nothing. So I again remove the transistors and the diodes this time and again found the the 2N2219 was damaged so I replaced it again and re fitted the diodes. Again, no output.
The only thing that I couldn't test was the op amps so I went and purchased 6 new ones and fitted them and again no output. So I searched the internet for a way to test them and found several circuits which I built (except the ones that required a dual supply) and began testing op amps but honestly none of these test circuits left me confident that all of my op amps were working. The new op amps returned the same output as the the old ones which I was convinced had to be blown so what now?
I then contacted Swagatam from Homemadecircuits. com (I have been following his site for many years) and asked him if he had a circuit that could test op amps that I could be confident with. Swagatam has been around for years and him and his team publish new circuits every week for the hobbyist and explains them so well that even I can understand what he is getting at. If you have not come across him his site it is worth a look. Anyway he sent me an op amp test circuit and instead of the usual voltage divider with 2 resistors this one used 2 10k liner pots and 2 LED's and by playing with the pots you can get the op amp to vary it's status and move from one LED to the other. I now know that all of my op amps are working as they should so back in they went. I have a fairly large bag of old pots that some of them don't have identification on them any more. So I hauled out my trusty Fluke and started testing until I found 2 10k pots and then breadboarded Swagatam's circuit. While I was testing these pots I came across 2 that were not working correctly, one was really jittery and the other was just dead. This got me thinking that the only parts that I have not tested on my power supply were the pots. So I hauled them out and tested them. The voltage adjust pot turned out to be a 10k log pot. From pin 1 to pin 3 I measured 9.95k and between pin1 and 2 it went from zero to 9.9k very smoothly and predictably. The pot for the current adjust measured 9.9k between pin 1 and 3 and from pin 1 to 2 I got nothing. From pin 2 to 3 I also got nothing. It was as though the wiper had been removed. I had a 10 turn 10k linear pot in my bag so I fitted that as the voltage adjust pot and took the original voltage adjust pot and fitted it as the amp adjust pot. I connected a 16 voly 1 amp transformer to test and lo and behold I got a 0 to 17 volt output. If I wind the amp pot all the way down then the current overload led comes on. So I connected a 12 volt 0.7 amp bulb to it an tried it. The light started to glow at 3.5 volts and as I increased the voltage the current limit would come on so I would increase that a bit and so on. I took the voltage up to 14.2 and monitored as I went along. I eventually had a very bright light drawing .72 amps. I kept it running for about half an hour and monitored temperatures. The op amps stayed cool, U3 was very slightly warm to the touch and the only thing that got too hot to hold were the rectifier diodes. So now I got brave (or stupid depending how you look at it) and connected my 31 volt transformer. I did the same test as before and got the same performance and results. U3 gets a little bit warmer but not uncomfortably so but the rectifier really does get hot. When my new 28 volt transformer arrived I will use that from now on. So there we have it, a fully functional power supply risen from the dead.
I cannot thank you enough for all the help and guidance and encouragement that you and the other posters on this site have given me and I hope that you and the others will continue to help us morons for a long time to come.
Stay well
Very best regards Patrick