For 0 KOhm :

I don't know what that means but generally, you want to measure the voltage on the 3-terminal regulator's input, adj and output pins (not copper traces) and go from there.

 

I don't know what that means but generally, you want to measure the voltage on the 3-terminal regulator's input, adj and output pins (not copper traces) and go from there.

Hi dannyf,
I've still the same measures ....

Joined tests taken on pot leads, and always 34,4V on both leads A and B, and also 0V from A to W leads....

Next step?????

Thanks a lot.

jm

 

For 0 kOhm from adj to ground, you measure 34.8V. One of those two is wrong as you cannot get 34.8V across a short circuit

Hi Albert,
I've still the same measures ....

Joined tests taken on pot leads, and always 34,4V on both leads A and B, and also 0V from A to W leads....

Next step?????

Thanks a lot.

jm

 

If your using the 338, change the 220 ohms to 120 ohms per datasheets.

 

If your using the 338, change the 220 ohms to 120 ohms per datasheets.

Hi,

LM317 on this pcb...
Thanks.

jm

 

What voltage do you have across the 220 ohm resistor. 1.2 V?

 

always 34,4V on both leads A and B, and also 0V from A to W leads

Just to clear, if you measure the voltage between A and ground, or between B and ground, they both read 34V?
From the schematic, one of them is supposed to be connected to ground so CANNOT have 34V to ground.

Please connect negative meter lead to ground then, with power off, connect positive meter lead to each of A and B and record the resistance reading.
Then select the voltage range on the multimeter, turn the power on, and connect the positive probe to each of A and B and record the voltage.

 

What voltage do you have across the 220 ohm resistor. 1.2 V?

Hi KeepItSimpleStupid,

0V accross this resistor.

Thanks.

jm

 

Just to clear, if you measure the voltage between A and ground, or between B and ground, they both read 34V?
From the schematic, one of them is supposed to be connected to ground so CANNOT have 34V to ground.

Please connect negative meter lead to ground then, with power off, connect positive meter lead to each of A and B and record the resistance reading.
Then select the voltage range on the multimeter, turn the power on, and connect the positive probe to each of A and B and record the voltage.

Hi Albert,

So V A / ground = 34.23V Resistance: 1.14 MOhm - MegaOhm or MegOhm, don't know the right unit? -

V B / ground = 0V Resistance: 0 MOhm Point B must be grounded ?


Last measures were between A and B, not between these points and ground; of course it seems to be useless.

And also between wiper and point A .....

Apologies if my crude schematic, induced you in error.

Thanks a lot .

 

So V A / ground = 34.23V Resistance: 1.14 MOhm - MegaOhm or MegOhm, don't know the right unit? -

V B / ground = 0V Resistance: 0 MOhm Point B must be grounded ?

So the pot is open circuit - which would cause all the other effects.
Point B to ground 0 ohm, point A to ground 1 Mohm, therefore the pot must be at least 1 Mohm and not the 4.7k it is supposed to be.

 

So the pot is open circuit - which would cause all the other effects.
Point B to ground 0 ohm, point A to ground 1 Mohm, therefore the pot must be at least 1 Mohm and not the 4.7k it is supposed to be.

I'm going to desolder it, control it's resistance and then replace it.

Thanks.

jm

 

've still the same measures

Which is what?

Joined tests taken on pot leads, and always 34,4V on both leads A and B, and also 0V from A to W leads....

No idea what A, B, or W is.

I think you are making it quite hard for others to help you, by assuming others know what you mean. We only have the schematic to go by. So a much easier approach wo7ld be to refer, always, to the schematic when providing information. Otherwise, you provide more confusion.

 

So the pot is open circuit - which would cause all the other effects.
Point B to ground 0 ohm, point A to ground 1 Mohm, therefore the pot must be at least 1 Mohm and not the 4.7k it is supposed to be.

Hi albert,

As i am also a lucky guy, my 4.7KOhm has burnt !!!!!!!!!!!!!

Going to buy others, as evidently no spare parts in my box.

Thanks for your help, albert and others members of this forum.

jm

 

As i am also a lucky guy, my 4.7KOhm has burnt !!!!!!!!!!!!!

Going to buy others, as evidently no spare parts in my box.

When you fit a new one, set it to the mid-position and don't move it until you have a correct output voltage of around 15V. This will prevent the new pot being damaged if there is another fault.

 

Which is what?



No idea what A, B, or W is.

I think you are making it quite hard for others to help you, by assuming others know what you mean. We only have the schematic to go by. So a much easier approach wo7ld be to refer, always, to the schematic when providing information. Otherwise, you provide more confusion.

Hi Danny,

Points A, B , W are points of pot schematic - see picture joined -

I'm trying to be clearer for all, next time.

Thanks alot.
jm

 

When you fit a new one, set it to the mid-position and don't move it until you have a correct output voltage of around 15V. This will prevent the new pot being damaged if there is another fault.

I choose 3 '' good pot " , i hope so ...

First: http://www.reichelt.de/6mm-Pots-mon...RTICLE=88204&GROUPID=3135&artnr=PO6M-LIN+4,7K

Second: http://www.reichelt.de/Multi-Turn-P...ARTICLE=54295&GROUPID=3138&artnr=P4W-LIN+4,7K

Third: Multiturn, costly, but for precise setting, worth money?

http://www.reichelt.de/Multi-Turn-P...LA=2&ARTICLE=2545&GROUPID=3138&artnr=534-5,0K

Is it good components for this use?

Thanks a lot.

jm

 

Any of them will do the job. It will be easier to set a precise voltage with the multi-turn one. It's up to you.

 

Hi all,

Bought and received new pots, and still the same end: burnt with white smoke!!!!!!!

With pot set initially ad mid course, output display was: 33.6V.

Joined a short resume of measures.

I've still 4 more pot, but i don''t like black smoke ...............

Thank for your help.

jm

 

Hi all,

I desoldered the pot to verify resistance, or short circuit ....

5,45 KOhm from pt A to B

Resoldered it :

A to ground 12.8 KOhm B to ground 0 Ohm

Power on :

A to ground 34.58V Wiper to ground 32.3 V B to ground 0V


Also 34.4 V output display.

And now ?

Thanks.

jm

 

Hello,

How did you measure the Vref?
In the table you say Vout = 33.7, Vadj = 33.18.(for 0Ω and 2.3 kΩ).
When I subtract 33.18 from the 33.7, I get 0.52 and not the Vref you mention.
Please measure the voltage at the LM317 output itself.

Bertus