Troubleshooting LPT46 40w power supply board (from powder coater)

[Beeker1-9]

Hello, I decided to get into powder coating as a hobby and as a way to make some extra revenue, so I bought an expensive used Nordson Surecoat powder coater which I was assured worked however when I plugged it in I saw a very quick flicker of the backlit screen then nothing. I took it apart and found the power supply board (LPT46) was not outputting the correct voltages (+5v +12v +24v) so I ordered a new LPT46 power supply board hoping that would fix the problem. When I received the new one I plugged it in and tried turning it on only to find it still was not operational. I then replaced the AC line filter as it was the only other component between the wall and the LPT46 40w power supply board (other than a mechanical switch which is working and tests 120v coming out of it) with no change.

When I try to bench test the LPT46 40w power supply board I hear a tiny *click* sound (almost like a tiny relay tripping/resetting) with a tiny spike of voltage at the output pins (about 0.5v for the duration of the click) then nothing until it clicks again (about every 3-4 seconds)

Here is a link to the LPT46 data sheet:
https://www.mouser.com/ds/2/633/lpt40series_ds_1184686732_ds-708059.pdf

Am I right to assume that both power supply boards are non-operational?

I found one wire from the output (SK2- pin 5) had come loose and was pushed back into an unused spot on the connector that goes to an unused pin on the control board (pretty sure this caused the replacement LPT46 board to fail)

Is there any special procedure for testing this LPT46 power supply board beyond hooking it up to power and checking its output pins with a multimeter? I don't have much of a background in electronics other than a lot of DIY repairs mainly involving observational testing.. I have always wanted to get into electronics as a hobby but as of yet I have only tinkered with fixing stuff when it breaks..

As far as I can tell I don't believe either LPT46 is functioning properly, I just don't want to buy ANOTHER one to try only to find out one (or both) of these LPT46's I have are operational and not be able to return any of them..

Any help you can provide is GREATLY appreciated!

 

[4pyros]

I found one wire from the output (SK2- pin 5) had come loose and was pushed back into an unused spot on the connector that goes to an unused pin on the control board (pretty sure this caused the replacement LPT46 board to fail)

What did the loose wire touch? The data sheet says all the pins are used.
I can't tell from the data sheet but sometimes power supplies like these need a load to work properly.
If you are testing it the unit there may be a short in it somewhere causing your power supply to go into protection mode against overcurrent, and keep keeps trying to come on and when it sees the short it shuts down again.
There is most likely something in the unit making the power supply fail.

 

[alec_t]

I can't tell from the data sheet but sometimes power supplies like these need a load to work properly.

According to the datasheet the minimum loads on the outputs are :-
5V------ 0.4A
12V-----0A
24V-----0.1A

 

[4pyros]

According to the datasheet the minimum loads on the outputs are :-
5V------ 0.4A
12V-----0A
24V-----0.1A

What alec said, guess I did not have enough coffee yet.

 

[Beeker1-9]

I am trying to test it without it being plugged into the rest of the unit. The control board for the powder coater has a 7 pin connector that the 6 pin output from the powder supply connects to, the loose wire was mistakenly pushed into the unused pin on the 7 pin connector into the control board

 

[Les Jones]

Which pin on the plug that connects to the power does the loose wire connect to ?
To test the power supply on the bench load the 5 volt rail with a 10 ohm resistor of at least 3 watts power rating. ( this will draw 0.5 amps.) Load the 24 volt rail with 220 ohm resistor with at least 3 watts power rating. (This will draw about 0.11 amps.)

Les.

 

[KeepItSimpleStupid]

I think Les nailed it. The datasheet says the pin is one of the grounds.

What is unusual for this supply is that the sense leads don't have to be connected.

 

[Les Jones]

Hi KISS,
I don't think I understand this disconnected wire yet. My understanding at the moment is that there is a 6 pin connector at the power supply end of the cable and a 7 pin connector on the control board end. If there is a seventh wire at the control board end then where does it connect to at the 6 pin plug end ? (Power supply end.) If it is connected to one of the positive power supply output pins at the power supply end then the unconnected end at the 7 pin plug end could have shorted to ground destroying both power supplies. I think Alec's idea that the power supplies are not working as there was no load on them when bench tested is a more likely explanation. Regarding the supply working without the need for the sense terminals being connected I think it will have resistors fitted connecting the sense terminals and the power supply outputs. I have seen this on some power supplies. It avoids the output going up to some excessively high voltage if a sense wire becomes disconnected. ( I have seen a satnav destroyed when the sense wire fractured which applied almost 12 volts to it instead of 5 volts. This would not have happened if there had been a resistor fitted between the sense input and the power output.)

Les.

 

[KeepItSimpleStupid]

Hi KISS,
I don't think I understand this disconnected wire yet. My understanding at the moment is that there is a 6 pin connector at the power supply end of the cable and a 7 pin connector on the control board end. If there is a seventh wire at the control board end then where does it connect to at the 6 pin plug end ? (Power supply end.) If it is connected to one of the positive power supply output pins at the power supply end then the unconnected end at the 7 pin plug end could have shorted to ground destroying both power supplies. I think Alec's idea that the power supplies are not working as there was no load on them when bench tested is a more likely explanation. Regarding the supply working without the need for the sense terminals being connected I think it will have resistors fitted connecting the sense terminals and the power supply outputs. I have seen this on some power supplies. It avoids the output going up to some excessively high voltage if a sense wire becomes disconnected. ( I have seen a satnav destroyed when the sense wire fractured which applied almost 12 volts to it instead of 5 volts. This would not have happened if there had been a resistor fitted between the sense input and the power output.)

Les.

Missed that. The "unused pin" may be connected to nothing.

Everything else makes sense.

 

[4pyros]

Missed that. The "unused pin" may be connected to nothing.

Everything else makes sense.

Alright Les back to what I said, I think you may mat have a short in your unit and you need a load to bench test that PSU. Can you check either one?

 

[Beeker1-9]

OK, thanks for the help so far everyone!

I did not have any resistors available for testing so I used two potentiometers setup like a variable resistor one set to 10ohm the other set to 220ohm and connected one outer pole of each potentiometer to the PSU ground, the other pole I placed in the connector of the respective pin (10ohm in one of the +5v output pins [SK2-2/SK2-3], 220ohm in the +24v output pin [SK2-1]) the PSU continued to do the same thing it did before *click* (outputs between 0.7v- 7v max on the +24v output pin [SK2-1] for the duration of the *click*)

I only had the 10ohm load connected to one of the two +5v output pins at a time (would it matter that it's not connected to both at the same time?)

This test was with the original LPT46 PSU from the unit, not the replacement one I purchased (in case I did this test wrong I did not want to damage the replacement)

At this point I'm considering both PSU's to be bad and that I need to purchase another LPT46 to test the unit, does this sound correct?

As for the previously loose wire, the control board of the powder coater has a 7-pin connector that the 6-pin output from PSU connects to, the 7th pin is on the control board but is blank on the connector. I believe the wire came loose when I "diagnosed" the unit previously and I hastily crammed it into the wrong port of the plug going into the control board. The PSU connector is only 6-pin with all pins being used..

 

[Les Jones]

The two + 5 volt pins on the power supply are probably connected together. (You can easily check with a multimeter between the pins or by looking at the PCB track on the board where it connects to the pins) If they are connected together then the way you performed the test is OK. (I think it very unlikely that there are two independent +5 volt outputs.) Which pin on the power supply did the wire that became disconnected at the control board end connect to ?

Les.

 

[4pyros]

I believe the wire came loose when I "diagnosed" the unit previously and I hastily crammed it into the wrong port of the plug going into the control board.

This could be bad, was power on?

 

[Beeker1-9]

The two + 5 volt pins on the power supply are probably connected together. (You can easily check with a multimeter between the pins or by looking at the PCB track on the board where it connects to the pins) If they are connected together then the way you performed the test is OK. (I think it very unlikely that there are two independent +5 volt outputs.) Which pin on the power supply did the wire that became disconnected at the control board end connect to ?

Les.

I found one wire from the output (SK2- pin 5) had come loose

The misplaced wire was in place (in the wrong spot) when I installed the new PSU and tried to power it on with no success. There was no flicker of lights or any signs of failure other than it just plain not working.. I later noticed the mistake and pin'd it back into its proper pin. Amateurs.

 

[Les Jones]

That pin is one of the common (Ground) pins on the power supply so if it shorted to ground it would not cause a problem. If it shorted to one of the pins connected to one of the powersupply output pins then it could damage the power supply.

Les.

 

[Beeker1-9]

Unfortunately I can't tell what the unused pin connects to as its a multi-layer board so I cannot visually trace the pin on the board.. I guess I could check continuity between it and the other power pins..

 

[Beeker1-9]

Alright, I checked continuity between the unused pin on the board that I accidentally shorted SK2-pin 5 to and on the controller board it shares continuity with pin SK2- pin1(+24v) and SK2- pin4(common)

I checked the continuity of the cable attaching the two boards together and it checks out (no pins shorted to each other)

I checked the continuity on the PSU as follows:
[All pins on SK2 connector]

Pin 1 has momentary continuity with pin 2 & pin 3 (sometimes momentary pin 4)
Pin 2 has continuity with pin 3, momentary pin 1, sometimes momentary pin 4
Pin 3 has continuity with pin 2 & momentary continuity with pin 1 & sometimes momentary pin 4
Pin 4 has continuity with pin 5 sometimes continuity with pin 1
Pin 5 has continuity with pin 4 (sometimes momentary cont pin 1 & 2)
Pin 6 has continuity with nothing

I think that confirms this PSU (original) is bad. Correct?

PSU # 2
[All SK2 pins]
Pin 1 momentary continuity with pin 2 & 3
Pin 2 momentary continuity with pin 1 &3
Pin 3 momentary continuity with pin 1, continuity with pin 2 sometimes momentary pin 4
Pin 4 continuity with pin 5
Pin 5 continuity with pin 4
Pin 6 continuity with nothing

Am I correct in summizing that both PSU's in this case have been shorted out and I should purchase a new one?

Thank a lot for all the help! Its rewarding to try to diagnose this with the help of you all instead of just dropping it off and having it fixed for waayy too much (they never even got back to me with a quote or anything in regards to repair!) Hopefully we can properly diagnose this as I just got home from spending 7.5 hours stranded in 10°F weather with a broken down car 2 hours from home (ended up replacing fuel pump & filter in a parking lot to no avail before finally having to call a ride from 2 hours away, NOT FUN!) So it will be refreshing to properly diagnose SOMETHING and hopefully give me the energy to figure out these other troubles.. Going back in the morning to tow it home.. After my toes thaw out!

Thanks again for all the help. It means a lot to be able to get help from such knowledgeable people!

 

[Les Jones]

In your fist sentence you say "it shares continuity with pin SK2- pin1(+24v) and SK2- pin4(common)" This statement implies that there is continuity between +24 volts and common. If that is the case then there is a short on the controller board between. When you say continuity what value of resistance are you considering as continuity ?

Les.

 

[Beeker1-9]

I'm just using the continuity function of my multimeter.. If it beeps I consider it having continuity.. Forgive me for my simple understanding of electronics testing, all my experience is what I've learned hands on over the years..