Electronics > Repair
Korad KA3005P power supply faulty/repair
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alm:
Like I said, I would trace the voltage measurement connections and go from there. There are likely thin traces coming from J2 (or the input header) going via some resistors to U10. See if there are any active components on this path, check resistors and check if the U10 input gets a stable DC voltage (probably varying between 0-5 V or so, scaling linearly with the output signal).

The fact that voltage regulation appears to be independent of voltage measurement argues against the MCU in the regulation loop in my opinion. Why would you waste two ADC inputs on sensing the output voltage?
cavlovic:

--- Quote from: alm on October 23, 2013, 04:44:01 pm ---Like I said, I would trace the voltage measurement connections and go from there. There are likely thin traces coming from J2 (or the input header) going via some resistors to U10. See if there are any active components on this path, check resistors and check if the U10 input gets a stable DC voltage (probably varying between 0-5 V or so, scaling linearly with the output signal).

The fact that voltage regulation appears to be independent of voltage measurement argues against the MCU in the regulation loop in my opinion. Why would you waste two ADC inputs on sensing the output voltage?

--- End quote ---

I did listen to your advice and traced J2 to U10, through a couple of resistors and caps, but there are no active components in the path.

Then I spent 4 additional hours trying to figure out what is wrong (it was PITA to measure while unit is powered on since there is very little space, even though I have a set of really thin probes), and I may be onto something (my 4 hours equate to maybe a couple of minutes to some of you here, so please bare with me :D).

Voltage set and detection part:
Both outputs of U5 opamp are used for voltage regulation and display. Output 1 (PIN 1) goes from 0.04v (0v set output voltage) to 2.84v (31v set output voltage) and this output is only dependent of set voltage, regardless of load. Output 2 of U5 reads 0.7V to 1.16V, also jumping all over the place, and this opamp output is dependent of the load, and this should be the one that causes voltage reading problems. Output 2 of U6 also reads 0.04v to 2.84v and this one is not dependent of the load attached.

Current set and detection part:
Output 1 of the U6 reads 0.04v (0amps set current) to 2.56v (5.1amps set current). Same goes for output 1 of the U7. Both of them are not dependent of the load and represent just set current values. Output 2 of U7 reads -3v to 2.71v and this one is load dependent and probably is used for displaying actual current flow. This reading started acting up today also, so both voltage and current readings are off, even though they are spot on to set values.

I believe that both output for voltage and current when load is present should read almost identical to their set values (0.04v-2.84v for voltage and 0.04v-2.56v for current) if opamps didn't fail.

I guess those opamps need replacement, and they are causing  all the trouble. I also may be off my path here, so any input is much appreciated.

Also, if anyone happens to have Korad KA3005P or D laying around, measuring output 2 (PIN 7) of both U5 and U7 under load, from minimum to maximum voltage and current would help me a lot.

Thank you all,
Balsa
KORAD TECHNOLOGY:

--- Quote from: cavlovic on October 20, 2013, 05:13:03 pm ---I got this power supply a couple of days ago and it worked well until today. I tested it by charging almost empty 72Ah car leadacid battery at 14V 4-5A, under supervision a few times. It worked all well.

Today when I try to do the same thing, once output is turned ON voltage readings are way off of actual voltage. Output on Korad reads 6-7 volts (14V set voltage) and my multimeter reads almost 13V (which is fine as battery is not fully charged).

I also measured current and it reads fine on both Korad and my multimeter. Only voltage reading is way off.

I believe it needs to be calibrated, but not sure how it got so messed up in a few days. I tried to find any information on calibration all day long, but had no luck. I also dissembled the unit but didn't find any obvious pots for adjustments, which led me to believe that it should be done through software or some kind of key combination. Does anyone know how to do this? Manual is all in chinese and I doubt it contains information about calibration.

Also, software which comes with this unit is complete garbage. It's half scrambled and unreadable and it also doesn't function at all. I need to change location to some automatic log location, but I can't seem to be able to do it, so I can only start unit from software but not adjust voltages and current.

Is there any other software that can be used with this Korad KA3005P power supply?

Thank you!

--- End quote ---



This is Krissy from KORAD TECHNOLOGY. Would you please kindly send me your e-mail address? I want to solve it soonest. Thank you in advance!
cavlovic:

--- Quote from: KORAD TECHNOLOGY on October 25, 2013, 04:04:49 am ---
--- Quote from: cavlovic on October 20, 2013, 05:13:03 pm ---I got this power supply a couple of days ago and it worked well until today. I tested it by charging almost empty 72Ah car leadacid battery at 14V 4-5A, under supervision a few times. It worked all well.

Today when I try to do the same thing, once output is turned ON voltage readings are way off of actual voltage. Output on Korad reads 6-7 volts (14V set voltage) and my multimeter reads almost 13V (which is fine as battery is not fully charged).

I also measured current and it reads fine on both Korad and my multimeter. Only voltage reading is way off.

I believe it needs to be calibrated, but not sure how it got so messed up in a few days. I tried to find any information on calibration all day long, but had no luck. I also dissembled the unit but didn't find any obvious pots for adjustments, which led me to believe that it should be done through software or some kind of key combination. Does anyone know how to do this? Manual is all in chinese and I doubt it contains information about calibration.

Also, software which comes with this unit is complete garbage. It's half scrambled and unreadable and it also doesn't function at all. I need to change location to some automatic log location, but I can't seem to be able to do it, so I can only start unit from software but not adjust voltages and current.

Is there any other software that can be used with this Korad KA3005P power supply?

Thank you!

--- End quote ---



This is Krissy from KORAD TECHNOLOGY. Would you please kindly send me your e-mail address? I want to solve it soonest. Thank you in advance!

--- End quote ---
PM sent.
mos6502:

--- Quote from: KORAD TECHNOLOGY on October 25, 2013, 04:04:49 am ---This is Krissy from KORAD TECHNOLOGY. Would you please kindly send me your e-mail address? I want to solve it soonest. Thank you in advance!

--- End quote ---

What is your policy regarding schematics? Can you give them out or not?
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