Author Topic: Permanent CC and no output [Longwei K3010D]  (Read 13086 times)

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Offline terry-moreau

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  • Country: ca
Re: Permanent CC and no output [Longwei K3010D]
« Reply #25 on: November 10, 2022, 01:20:17 pm »
I had the exact same issue!  My LongWei LW-K3010D was stuck with current limit red LED on, and unresponsive to anything.  I did continuity check on flyback transformer winding, and the same -5V winding output was open on the bottom side, but connected on the tops side.  T1 looks obvious installed on an angle and pins on one end not pushed through the board all the way.  Bottom side solder was not connecting to some T1 secondary pins, and they need to be!  Thanks to post your issue, and to everyone's troubleshooting suggestions.  I was going to toss my supply in garbage, but instead I fixed in less than 1 hour, thanks to Google search bringing me here.   :)
 

Offline jeeek

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  • Posts: 2
  • Country: ph
Re: Permanent CC and no output [Longwei K3010D]
« Reply #26 on: January 04, 2023, 01:16:41 am »
do you have any idea what is the value of T2?
 

Offline ysg2k6

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  • Country: hk
Re: Permanent CC and no output [Longwei K3010D]
« Reply #27 on: May 22, 2023, 08:36:54 am »
Pin #8    0.2 VDC
Pin #9    0.8 VDC
Pin #2    1.75 VDC
Pin #1    1.2 VDC

Pin #16    5.1 VDC
Pin #4    60kHz 10% PWM
Pin #5    60kHz sawtooth 1 to 3.5V
This means U4 is correct

Pin #11 and #14     0.2 VDC

There is no reaction on U4 pins to pots position.

it was tested that Pin#2 is 1.75V, and @lolocoian tested to be 2.14/2.25V something, how could it be? it is clamped at 7.5V by D4 !!!
 

Offline JohnP

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  • Country: nl
Re: Permanent CC and no output [Longwei K3010D]
« Reply #28 on: May 24, 2023, 07:29:04 pm »
Here's some more information I've gathered about the voltage dropping (for me @11Vdc).
First of all, it is wise to see which circuit board you have, which version number.

There have been some changes to newer versions from that diagram posted here.
The most important thing in this is the adjustment of 7.5 V and the Ref voltage of pin 16 is omitted and instead a second TL431S with a ref voltage of 5V on the potentiometers etc. The problem I found here is that the ref (2,5V) of U7 (2nd TL431S) is not stable. I solved this by placing an RC over R80 (1K and 100nF). This seems to work. Also check/replace R59 2.0K.

I also adjusted the diagram a bit for my circuit board LW-305D-1 Rev 20191108.
This could help some people.
« Last Edit: September 13, 2023, 08:23:19 am by JohnP »
 

Offline Travis4

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  • Country: us
Re: Permanent CC and no output [Longwei K3010D]
« Reply #29 on: October 15, 2024, 02:10:45 pm »
Hello, I too have an issue with a LongWei Power Supply and am in search of an updated schematic. The closest I have found was this excerpt above posted by John P. My board is marked LW-K305D-1 Rev 20210330 and has the extra TL431 etc.
The problem is this: Apparently works fine except when you press the OUTPUT button which connects the load the voltage jumps up about 10% and then holds steady for about 10 seconds. Then drops to the proper voltage for a fraction of a second before returning to the higher voltage. Display readings match independent measurements on the load and look clean on a scope. It happens at low and high currents.
The 5.11 ref voltage produced by the TL431 remains steady. Any thoughts?
 

Offline Travis4

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  • Country: us
Re: Permanent CC and no output [Longwei K3010D]
« Reply #30 on: October 16, 2024, 04:26:02 pm »
As a follow on - I am pretty sure the problem lies in the encoder/display section and that the PSU board itself is fine. The voltage matches what is displayed but the display ( ie voltage setpoint ) has a mind of its own and jumps between 2 constant values above and below the initial setpoint. After many minutes it settles down and operates normally. I expect this will get worse over time but might be indicative of the problem now. If I had not exhausted my freeze can supply I would be hitting the electrolytics to  see if I could identify a bad one.
The board is all surface mount and really the only thing I have a chance of replacing are the larger electrolytic cans (still surface mounted) as I have twisted similar ones off in the past and replaced with through hole units.
 


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