Permanent CC and no output [Longwei K3010D]

[terry-moreau]

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.   

[jeeek]

do you have any idea what is the value of T2?

[ysg2k6]

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 !!!

[JohnP]

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.