Set the pot to mid range AND DO NOT ADJUST IT AT ALL until the output voltage is around 14V. This will prevent damage to the pot.

Disconnect the wire I have marked with a red cross in the attached copy of the schematic - everything else should stay connected as it was.
Let us know the voltages on the three pins of the regulator.

 

My usual suggestion which proved right for me in the last maybe 30 years if not more: throw that awful circuit out to the window, and forget it! You have demonstrated it is wrong.

Implement again the whole thing with new components (initially with fixed-known-value resistors). Solder components to each other, or use a neat tidy perfboard.

In all the years I spent in four different forums, the LM317 based PSUs, rank in the top of "not working first time implementation" list. Check pin out (high chances you have it wrong).

When you have it working, then, and not before, add the pot (which uses to be the origin of many of the problems).

 

When a component burned up, it is never the right solution to solder in another one. You will need to figure out what happened.

I said this earlier, you have made it quite difficult for others to help you: you said a lot without providing any useful information about your circuit and your measurements. For example, it seems that your are trying to measure resistance with the circuit powered on.

I would suggest that you back to basics:

1. Read the data sheet and see what the minimum load current needs to be. Your R1 is too big for example.
2. Calculate the power dissipation on the pot and bypass it with a known value resistor. Measure the voltage on the input, output and adj pins.

Remember, when you don't know what you are doing, do nothing is the optimal strategy.

 

Set the pot to mid range AND DO NOT ADJUST IT AT ALL until the output voltage is around 14V. This will prevent damage to the pot.

Disconnect the wire I have marked with a red cross in the attached copy of the schematic - everything else should stay connected as it was.
Let us know the voltages on the three pins of the regulator.

Hi Albert,
Once again this damned pcb is grrrrrr...................

Set post to mid range so 2.2 KOhm - checked with dmm before soldering it -

Output display is only 33.6V and doesn't move to another value....

V ref 1.36V Vadj 33.01 V V Ouput 33.5V V Input 35.00 V



Base disconnected as asked:

V ref 1.33 V Vadj , V Output, and V Input are nearly identical.


Albert, thanks for you invaluable help - as others members of this forum - but i think i'm gonna to follow these steps:

- Since minimum batch bought is 5 pcb, i 'm going to build another with a new one

- Replace 230VA trafo with 80 VA by example

- Replace 4.7 KOhm potar with a trimmer soldered on pcb

- Test it , for this '' derated '' psu.

- Then, if previous steps ok, going to 230VA and 4.7 KOhm


I think it's a clever methodology, cause as anyone i hate wasting my time, and also time of posters of this forum.

Do you agree?

I don't understand why i build the same pcb - for 80VA only and trimmer pot soldered on pcb - and it works, and now not !!!!!!!!!!

Thanks a lot, and nice day.

jm

 

My usual suggestion which proved right for me in the last maybe 30 years if not more: throw that awful circuit out to the window, and forget it! You have demonstrated it is wrong.

Implement again the whole thing with new components (initially with fixed-known-value resistors). Solder components to each other, or use a neat tidy perfboard.

In all the years I spent in four different forums, the LM317 based PSUs, rank in the top of "not working first time implementation" list. Check pin out (high chances you have it wrong).

When you have it working, then, and not before, add the pot (which uses to be the origin of many of the problems).

Hi augustin,

As i said to albert, i don't know why this damned pcb isn't working, as a '' derated '' psu identical as it , is good ??????????

Power is only 80VA and set to 12V, and up to now it works, so ?????????????

I'm building a new one with 80VA and trimmer sold on it, and after it works, going to 230VA and 4.7 KOhm pot.

I think it's a right way to get the job....

Thanks for your advice and help.
jm

 

Set post to mid range so 2.2 KOhm - checked with dmm before soldering it -
Output display is only 33.6V and doesn't move to another value....
V ref 1.36V Vadj 33.01 V V Ouput 33.5V V Input 35.00 V

Base disconnected as asked:
V ref 1.33 V Vadj , V Output, and V Input are nearly identical.

So it seems the problem is with the LM317. It may be faulty or its leads connected incorrectly. Check the connections as below:

 

So it seems the problem is with the LM317. It may be faulty or its leads connected incorrectly. Check the connections as below:
View attachment 109054

Hi Albert,

I check connections one more time, and there's no mistake.

I'm going to change LM317 ....


This morning, i replaced pot 4.7 KOhm with two 2.2 KOhm 2W fixed resistors soldered in serial.

Base deconnected : V adjust/ground 32.7V Vouptut/ground: 33.23V Vinput/ground:34.83V V ref: 2.48V????? Checked three times for this value.

Base connected: Same values and Vref still 2.48V


Still the same output display and no move.........


I'm going to draw a sketch, and joining it in a few minutes .




Thanks a lot.

jm

 

Hi all,

Replaced the damaged pcb by a new one; in fact, with soldering and desoldering, two coper tracks were broken on the lower pcb side.......

Now LM317 seems works fine, but still the same issue when measuring 2W Resistors - each 2.2 KOhm - to ground.

Must find , i think - 4.4 KOhm and 2.2 KOhm - right or wrong???

See sketch enclosed .

Output display is not 14 V , but beginning to a few volts and ending to 35V?????


Thanks a lot.

jm

 

Now LM317 seems works fine

So, with the pot replaced by two 2.2k resistors and everything connected you have 13.6V at the output?
If so, then it is now safe to fit a new pot. Start with it set to the mid-position and make sure you still have around 14V at the output.
If that is OK, then you can adjust the pot and your variable power supply should be fully functional.

 

but still the same issue when measuring 2W Resistors - each 2.2 KOhm - to ground.

What do you mean with that?

 

So, with the pot replaced by two 2.2k resistors and everything connected you have 13.6V at the output?
If so, then it is now safe to fit a new pot. Start with it set to the mid-position and make sure you still have around 14V at the output.
If that is OK, then you can adjust the pot and your variable power supply should be fully functional.

Hi Albert,

Now, i get:

V ref 1.24 V
V adjust / ground 12.31 V
V output / ground 13.60 V Identical as calculated with Vout= 1.25*( 1+(2200/220)) Calculus give 13.75
V input / ground 35.06V

V output display growing from 1.25 V to 35 V .


As i said before, i can't get an output display of 14 V, maybe i made something wrong with 2.2KOhm resistors or ???

Joined also pictures of 2.2 KOhm Resistors soldered, and wires connected to pcb...


Is there mistake(s) ?

Thanks a lot and nice day.

jm

 

There is one final check I would recommend to make sure all three output transistors are properly sharing. Connect a load to the output drawing perhaps 1 or 2 amps (set the output voltage suitable for the load - it doesn't matter whether what the voltage is). Measure the voltage across each of the 0.1 ohm resistors. The three voltages should be very similar to each other to indicate that the current is being shared by the three output transistors.

 

What do you mean with that?

Hi augustin,

Thanks for you help, first like Albert and others members of this forum.

I still have the same issue , can't get 4.4 KOhm from red wire - pt 1 in schematic joined and ground - only 2.63 or 2.9 KOhm...
Error from my side to '' thinking '' 4.4 or ???

Blue - Whiper in a real potentiometer - to ground - pt 2 in schematic - 2.6 KOhm, make sense for me. Right or wrong?

Brown to ground - pt 3 to ground - 0 KOhm make sense also. Ground to ground . Right or wrong?

Mistakes in connecting resistors through wires to pcb or ??????

Desoldered pt 1 to check 4.4 KOhm to pt 3, and i found this value... than resoldered it of course.

See files joined.

Thanks a lot and nice day.

jm

 

I still have the same issue , can't get 4.4 KOhm from red wire - pt 1 in schematic joined and ground - only 2.63 or 2.9 KOhm...
Error from my side to '' thinking '' 4.4 or ???

Pins 1 and 2 of the pot are connected together - so the 2.2k connected between pins 1 and 2 is short-circuited. Therefore your readings make sense and are to be expected. In any case measuring resistances in-circuit can be misleading as there are other paths that current can take.

If the output voltage is correct (~14V) then the resistors are doing their job correctly.

 

Pins 1 and 2 of the pot are connected together - so the 2.2k connected between pins 1 and 2 is short-circuited. Therefore your readings make sense and are to be expected. In any case measuring resistances in-circuit can be misleading as there are other paths that current can take.

If the output voltage is correct (~14V) then the resistors are doing their job correctly.

I'm going to search something as a load, in order to measure voltage about 0.1 resistors.

 

I'm going to search something as a load, in order to measure voltage about 0.1 resistors.

A car bulb?

 

A car bulb?

Yes, same idea... Thanks.

 

A car bulb?

LM317 input voltage/ ground is always 35V ,LM317 output voltage/ground is 13.65V, but display output is increasing for a few volts to 35V .

I have only 12 V bulbs, so make a scrap pcb with 2 x 820 Ohms 5W resistor in serial >>>>>>>>>>> suddenly output voltage display dropped to 0V!!!

I disconnected this load afraid of maybe an other issue!!!!

35:1640= 0.021 A so searched for a resistor of max value of 35 Ohm; of course, no so small value in my box.

What's the next step ??????????

 

What's the next step ??????????

Is the LM317 still disconnected from the output transistors? If so, reconnect and then see what happens.

 

Is the LM317 still disconnected from the output transistors? If so, reconnect and then see what happens.

No everything is connected, base, collector, emitter .