K40 lps

Hey Don,

I hope it is okay contacting you directly.
I purchased a brand new 40W Cloudray MYJG40 LPS. Unfortunately, this LPS does just nothing, even the Power LED stays off…
I measured the fuse, it is okay. I can measure 24V in the corresponding Outputs, but the 5V Line seems to be dead.
As you are the LPS expert, do you have any hint for me how to revive that LPS?
I already ordered another LPS, but as it will take weeks to ship to Germany, it would be great to get this one back to Life.

Thanks a lot & best regards!

A key mantra of this forum is to minimize direct posts so that the community can benefit from the activity herein.
Of course, I will help you in any capacity, or form that I can but I would prefer that you post this directly in the forum.

When you post in the forum here are some questions whose answers will help speed us to a solution.

Please post a picture of the connector end of your LPS while wired into the machine?

  • Has this supply been inoperable since you bought it?
  • Did you contact the seller for a replacement?
  • When did it fail?
  • Were there any unusual events that preceded the failure?

Note the power light is actually driven from the 5V supply, not the incoming AC, suggesting you have a bad 5V regulator

1 Like

See the attached schematic page.
Note that:
-the 5V supply is driven off the 24V supply (Red circle)
-the 5V when present illuminates the “Power” LED (green circle)

My best guess at this point is that the 7805 is bad.

What do you have connected to the 5V output?
Try disconnecting it and see if the5V returns.

@mcdanlj I don’t know if/how to move this thread into the main forum can you do that?

1 Like

Hi Don,

thanks for your reply.
There is no load on the 5V output, I am just measuring with my multimeter. 24V output is fine, 5V is 0.0.
As I have another LPS with an defective HVT, I just swapped the 5V regulator (7805). Unfortunately, same error.
As the fan is on the 24V line, it should run? On the fan-output, there is also no 24V.

Another LPS is already ordered, but I would like to understand whats going wrong here…

Thanks a lot!

Yes, the fan should run if you have 24V.

Need to answer this question:
The fan is connected directly to the +24V rail, which is connected to the 24V output. Why would there not be 24V at the fan connector when there is 24V on the output.

Be careful the 600V in this supply is lethal.

Well, just checked again:

  • 24V on Output Connectors: yes
  • 24V on Fan: no
    -5V on Output Connectors: no

According to the schematic above I also have no good idea what else may be wrong…
Don, want another LPS donated for experiments? :wink:

Sure I will take the donation but I have not given up finding it yet.
These symptoms dont make sense.

Can you trace the connection from the 24V output to the fan connector?
Perhaps my schematic is wrong.

You could measure continuity from the 24V output to the fan connector.

I will do that tomorrow :slight_smile:

I just checked a supply here and there is a short between the 24V output and the fan connector :thinking:

Also check the label on the fan to see if it is a 24V fan.

I wonder if some vintage of these supplies run 5V fans?

Also checked my supply: no short between 24V output and fan connector…
The fan itself is 24V.
I begin thinking the PCB is faulty somehow…

Did this supply ever work?

No, although it was purchased as brand new

Random thought…
What is the 115-230 input voltage selector set to ?

230 of course…

Your in europe?
You can pull out the PCB and visually trace the fan circuit.
It’s not clear to me what the fan voltage missing has to do with the 5V being missing?

Yes, Germany.
I will do that tomorrow and also get some pictures…

On my LAPS the 24V buss is connected through a jumper to the fan.
I wonder if that jumper is missing.

However if that jumper was not there the 12V would also not be working and 12V is used for the HV driver??

The fan and the 5V might be two separate problems.

No Jumper on my PCB.

So did you measure no continuity between those pads?

If they are not connected that is why you have no Fan voltage.