Problem with Korad KA3005D Power Supply

[eisi]

Hello everyone,

I recently acquired a Korad KA3005D power supply from an estate. Unfortunately, I'm experiencing some issues with it:

When I set the voltage/current and press the On/Off button, the voltage drops. For example, when set to 5V, the display shows only 0.9V after turning it on, and my multimeter confirms this reading.

Here are some steps I've already taken:

I tested the output with a 47-ohm resistive load, but the problem persists.
The issue only occurs above 1.95V; below that, it seems to work fine.

I plan to open the device and inspect some components. Any additional advice on what could be causing this issue and how to fix it would be greatly appreciated.

Thanks!

[eisi]

I also tried to perform the adjustment and heard a clicking sound from the relay when setting the maximum voltage range. However, I can't determine if it's both relays or just one. Nevertheless, I can only reach about 1.8V instead of getting anywhere near 30V.

My knowledge of circuit diagrams and troubleshooting is unfortunately not sufficient to proceed on my own, so I am grateful for any advice.

Best regards

[Poroit]

The relays clicking are from the protection circuit.
Does adjusting the current to a higher value increase the voltage output?
Look for damaged components.

[Poroit]

Post something on this as these guys are all over protection circuits for PS.
EEVblog Electronics Community Forum »Electronics »Projects, Designs, and Technical Stuff »fast CC/CV power supply..

[eisi]

The relays clicking are from the protection circuit.
Does adjusting the current to a higher value increase the voltage output?
Look for damaged components.

no it does not 

[exe]

If it's not covered with warranty, crack it open). Just be careful, there is lethal voltage inside.

It seems someone made schematic, this is very useful: https://www.eevblog.com/forum/repair/korad-ka3005p-power-supply-calibration/msg1109803/#msg1109803

I'm not familiar with this power supply.  But, since you asked my advice, let me re-iterate. So, below 2V the power supply is working normally, is that correct? Including current limiting mode?

[eisi]

That's correct.

[eisi]

When I turn the knob on the lab power supply beyond 2 volts, the display and the measured voltage jump to around 0.X volts. However, if I continue turning the knob, the output increases again. But it always only goes up to around 2 volts before it jumps back again.

[exe]

Just to confirm, current sensing and current limiting works as expected? Can you please double-check this for me? Can you pull, say, an amp of current or two?


Because if so, then it means that at least transistors on power board work correctly. What may not work is voltage range switching. Let me think what makes sense to check next. Just in case, I'd check that J1 connector cable (6 pins) on power board is fitted correctly on both sides.

[eisi]

Unfortunately, I can't draw enough amperage because I can only set the voltage up to a maximum of 1.9V and I don't have an appropriate load. While experimenting, I noticed the following:

When I connect a 21700 battery and set the device to 3.6V and 1A, the power supply's display shows 3.6V as expected.

However, when I connect my lowest resistance load and set the device to 1.9V (since I can't set it any higher) and 0.1A with OCP enabled, the power supply shuts off, which is expected behavior.

When I set the device to 10V without any load, turn on the output, and adjust the current from 0 to 5A in 0.1A increments, the voltage drops to 0V every 400-500mA. It's also worth noting that I never actually reach the 10V output voltage.

I hope this information is somehow helpful.

So I cant really say if current sensing/limiting works as expected, because of my limited knowledge to troubleshoot this 

[exe]

I can only recommend to check these voltages relative to "-" terminal on the power supply: Voltages on U5B inputs. One is from DAC (pin 5), another one is from voltage feedback (pin 6). The first one must be proportional to set voltage, the second one must be proportional to readback voltage.

But! If you are not comfortable working with the insides and not sure about safety precautions, I suggest not do it for own sake.