Permanent CC and no output [Longwei K3010D] - Page 1
Forum section: electronics / repair

author: czesio666
author_rank: Contributor
timestamp: October 25, 2019, 01:34:50 pm
content: Hi everyoneI have a problem with Longwei K3010D power supply. It shows permanent 0V and 0A and CC led is lit. No reaction to V and A knobs.I have found similar topic, read it and tried to follow suggestions.https://www.eevblog.com/forum/testgear/problem-power-supply-tech-star-k3010d/What i have checked:- there is no short on output, the resistance is ~160Ohm (two 330Ohm RA, RB in parallel for discharging output cap)- power mosfets and schottky are ok- 12V supply is ok- VR and AR pots are ok, they are correctly wired to the mainboard- U4 supply voltage is ok, reference voltage is ok- TL084 (LM324) seems to be ok, input voltages changes with V and A knobs- there is no output on SG3525, permanent zero with repetitive glitches, therefore the is no switching on power mosfets- U4 pin 1 is 0.6 to 2.5V sensitive to VR, pin 2 1.2 to 2.2V sensitive to VR, pin 9 is 0.7V,And I have no more ideas what to check.After switching on the fan starts spinning for a while (less than 1 sec). And then power supply is dead. One can hear the coil(s) sound and its frequency changing with current knob.Thanks for any ideasThe mainboard is K305D revision from 2019 so it is a little bit different than the one from the schematic. I observed that U1-B seems to be unused and there is no Q8, Q9, Q10, W2. U4_2 connected to R44 and D4_C

author: czesio666
author_rank: Contributor
timestamp: November 05, 2019, 01:40:02 pm
content: Should SG3525 always generate complementary signals on output? I have 0V on both output and I don't know if this indicates SG3525 failure.I can't figure out why CC led is on. Q6 is turned on which is controlled with U1-A output. How the current limit works?Edit: Ok, I get it. Outputs are shifted by period time. Max. 50% pwm can be generate on each output. Until inverting input of pwm is smaller than noninverting (sawtooth) the output is high.If I have 0% pwm on both outputs it means that inverting signal must be smaller than 1V (sawtooth signal on #5 is correct). I have 1.2vdc on #1 (inverting input) and 1.75vdc on #2 (noninverting input). Error amp gives permanent high output. Therefore PWM amp gives permanent low output.

author: Ordinaryman1971
author_rank: Frequent Contributor
timestamp: November 13, 2019, 03:49:53 am
content: Check if you have short on the output. There is a capacitor there and diode for reverse protection, check those two..Did you also check the wiring for cold solder joints. Check the ones that are there for voltage and for current sensing and for output. I would just try to resolder them and see if that will change anything.Some of those power supplies have something like a crowbar circuit that basically opens up if you overload it. You can't reset it by powering the power supply down, there are actual parts that brake down in the process...

author: czesio666
author_rank: Contributor
timestamp: November 19, 2019, 10:25:07 am
content: Thanks for replyI have already checked it. There is no short on output. Measured resistance is 170 Ohm, it means two discharging resistors in parallel, each 330 Ohm.Look at the schematic:I can't see any crowbar circuit in output section. There are only converter diodes D22 (are ok, checked after desoldering), discharging resistors RA RB, caps and sensing resistor (RL1 - two copper wires in circuit ). There is also reverse protection diode D30 (not in schematic). Working properly. When voltage is applied to output in correct polarity, the current is V / ( RA|RB). In reverse polarity voltage drops to 0,33V with current limit (diofe forward voltage).After powering on, current display shows 0,01 A and current limit turns on. I think there is something wrong with current control part that gives wrong information. Pots are ok.

author: BradC
author_rank: Super Contributor
timestamp: November 19, 2019, 11:26:53 am
content: What is the voltage on pin 8? If pin 9 is 0.7V that'd stop the PWM.

author: xavier60
author_rank: Super Contributor
timestamp: November 19, 2019, 12:16:52 pm
content: With the CC set to 10A, pin 2 of IC U1-A should be 100mV. 1.47mA sourced by Q1 through R4 is supposed to produce the 100mV

author: czesio666
author_rank: Contributor
timestamp: November 19, 2019, 12:27:15 pm
content: Pin #8 0.2 VDCPin #9 0.8 VDCPin #2 1.75 VDCPin #1 1.2 VDCPin #16 5.1 VDCPin #4 60kHz 10% PWMPin #5 60kHz sawtooth 1 to 3.5VThis means U4 is correctPin #11 and #14 0.2 VDCThere is no reaction on U4 pins to pots position.

author: xavier60
author_rank: Super Contributor
timestamp: November 19, 2019, 12:35:00 pm
content: With a + voltage on an op-amp's Inverting input, the output should be saturated negative.Is the negative rail OK? Maybe U1 is faulty.

author: czesio666
author_rank: Contributor
timestamp: November 19, 2019, 12:47:31 pm
content: U1 supply correct 12VCurrent pot set to max:U1-A #2 0.18VU1-A #3 0VU1-A #1 10.7V0.12V drop on R4Q1 open, 0.63V on BE, negative 6.4V CE

author: czesio666
author_rank: Contributor
timestamp: November 19, 2019, 12:59:43 pm
content: U1 Vcc- is not grounded.Corrected valuesCurrent pot set to max:U1-A #2 0.18VU1-A #3 0VU1-A #1 10.7V

author: xavier60
author_rank: Super Contributor
timestamp: November 19, 2019, 01:01:53 pm
content: Quote from: czesio666 on November 19, 2019, 12:47:31 pmWith 0.18V on pin 2, pin 1 should be saturated negative.

author: xavier60
author_rank: Super Contributor
timestamp: November 19, 2019, 01:05:06 pm
content: Does U1 have a negative rail?

author: czesio666
author_rank: Contributor
timestamp: November 19, 2019, 01:06:43 pm
content: Yes, the same thing is on U1-B.U1-C and U1-D seems to be ok.Ok, so I will replace TL084BC (LM324 is on schematic).U1 Vcc+ is 12V, Vcc- is 0.8V. Something wrong with supply?

author: xavier60
author_rank: Super Contributor
timestamp: November 19, 2019, 01:12:30 pm
content: Quote from: czesio666 on November 19, 2019, 01:06:43 pmYou will need to trace it, the schematic isn't clear about what supplies negative rail to U1.

author: Chris56000
author_rank: Frequent Contributor
timestamp: November 19, 2019, 01:52:10 pm
content: Hi!The Chinese might be good at designing cheap electronics (& counterfeiting it as well!!!) but their diagram & documentation skills are bloody atrocious!!The Op Amp Negative Supply is provided by D6 (SR1100), with reservoir capacitor C14 (100uF), with decoupling filter R30, the –12V for the op–amps @ pin 4 is across C8 at the junction of C8, R01 (2M2) and R30 (4R7) – this can be inferred from the low value of the –12V line decoupling–filter resistor!)I've got some nice Drawing Office Lettering now, so I'll get started on a new drawing in due course!Chris Williams

author: czesio666
author_rank: Contributor
timestamp: November 19, 2019, 01:57:55 pm
content: Vcc- goes to connector solder point named -5V. I think it is test point (the second one is 12V). Next it goes to R30/C8-. I found also that C6- is connected to the same node (the schematic is probably for older board revision).It looks like T1 with D5 D6 should produce positive 12V (this one is ok) and negative 5V? (this one is not ok). D6 is ok. Vcc- is 0,86V. But could it be due to U1 failure?

author: xavier60
author_rank: Super Contributor
timestamp: November 19, 2019, 02:06:23 pm
content: Quote from: czesio666 on November 19, 2019, 01:57:55 pmIs the winding OK?

author: czesio666
author_rank: Contributor
timestamp: November 19, 2019, 02:21:08 pm
content: Ok, i found it. Negative winding was not connected. Faulty joint. Resoldered and current limit disappeared. Now I will check if output is ok.

author: czesio666
author_rank: Contributor
timestamp: November 19, 2019, 02:37:54 pm
content: Tested with some load resistors and everything seems to be ok.The Vcc- is 4,8V.Thanks to all for help. regards

author: SirVer
author_rank: Newbie
timestamp: January 18, 2020, 11:34:43 am
content: Hello czesio,I seem to be having the exact same issues as you - knobs unresponsive, fans spin up for a second, coil hum is audible. You mentioned that it turned out to be your negative winding, and I'd like to check it on mine, but I'm kind of a noob and I don't know which winding that is - could you tell me which one it is? They all look fine visually, but I can't get at all of them with a multimeter without further disassembly, so I'd like to know which one I should go at first.Thank you in advance.

author: faza1111
author_rank: Newbie
timestamp: December 28, 2020, 12:47:54 am
content: I had 3 damaged smd capacitors, I changed all of them. There was probably a bad series of all capacitors

author: lolocoian
author_rank: Newbie
timestamp: July 05, 2021, 03:57:22 pm
content: I have the same PS and after months of use it has the following problem: When going up with the knob just above 12v it start giving random but lower than 12v readings in the display. Below 12v it works just fine, i know this is really poor information but maybe you can point me in the right direction as in to what i can check. I have only checked the potentiometer and it is fine, and also checked if i have short between Drain and Source on the two Mosfets and there is no short. Thanks in advanced!(Ps.: i also tested terminals in the big transformer in diode mode with my multimeter and it beeps and gives 000 reading, dk if that is normal or not! )TL084 has 12v on pin 4 and -4.22v on pin 11Across volt pot i have 3.25v and 5.27v when display shows 10v stable when i turn the knob to more than 12v it goes to lower voltages and the reading in the display is unstable and then i have in volt pot 1.19v and 5.36v in each connector.in amp pot i have 5.28 when in 10v stable and 5.36 when in random lower and unstable volt displaySG3525 pins when 10v stable:1=2.25v 2=2.25v 3=0v 4=0.51v 5=2.05v 6=3.8v 7=1.97v 8=1.46v 9=0.91v 10=0v11=0.04v 12=0v 13=12v 14=0.04v 15=12v16=5.18vand when things are unstable with knob turned past 12v but reading shows random voltage below 12vSG3525 pins1=1.7v 2=2.14v 3=0v 4=0.51v 5=2.05v 6=3.8v 7=1.97v 8=0.02v 9=0.58v 10=0v11=0v 12=0v 13=12v 14=0v 15=12v16=5.18v

author: xavier60
author_rank: Super Contributor
timestamp: July 06, 2021, 08:32:12 am
content: Become familiar with the workings of the SG3525,https://www.onsemi.com/pdf/datasheet/sg3525a-d.pdfPin 16 is the 5V reference out pin. It should stay very close to 5V and not fluctuate at all.The 5V reference supplies the top terminals of the VR and AR pots.The wiper voltage on both pots should smoothly increase from 0V to 5V as the pots are rotated from the fully CCW to the fully CW position.The VR pot seems faulty. One way of confirming is by swapping the pots.Actually "Across volt pot i have 3.25v and 5.27v when display shows 10v " is ambiguous. What are you measuring the wiper voltage with respect to?

author: xavier60
author_rank: Super Contributor
timestamp: July 06, 2021, 10:39:19 am
content: Pin 2 on the SG3525 should always be close to 7.5V as regulated by D4.

author: slntwater
author_rank: Newbie
timestamp: May 26, 2022, 09:09:18 am
content: Hi everyone!I also have a problem with my K3010D. I connected one of my LifePo4s (3,3V) with reverse polarity, the 2nd time now. After the first time, the 6A10 protection diode blew up, and everything was fine after soldering a new one.Now, after the second time (I know, i am a goat) the PSU seems to have a short curcit in it. It won't go over 0,03V and has always 10A CC. However, the regulation works, as I can move freely from 0-0,03V (respective 0-10A).All the components are looking fine, and I have no clue which components to test. Does anyone here have an Idea?Regards

author: terry-moreau
author_rank: Newbie
timestamp: November 10, 2022, 01:20:17 pm
content: 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.

author: jeeek
author_rank: Newbie
timestamp: January 04, 2023, 01:16:41 am
content: do you have any idea what is the value of T2?

author: ysg2k6
author_rank: Newbie
timestamp: May 22, 2023, 08:36:54 am
content: Quote from: czesio666 on November 19, 2019, 12:27:15 pmit 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 !!!

author: JohnP
author_rank: Newbie
timestamp: May 24, 2023, 07:29:04 pm
content: 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.

author: Travis4
author_rank: Newbie
timestamp: October 15, 2024, 02:10:45 pm
content: 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?

author: Travis4
author_rank: Newbie
timestamp: October 16, 2024, 04:26:02 pm
content: 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.