| Electronics > Repair |
| Permanent CC and no output [Longwei K3010D] |
| (1/7) > >> |
| czesio666:
Hi everyone I 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 ideas The 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 |
| czesio666:
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. |
| Ordinaryman1971:
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... |
| czesio666:
Thanks for reply I 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. |
| BradC:
What is the voltage on pin 8? If pin 9 is 0.7V that'd stop the PWM. |
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