EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: king on April 06, 2023, 08:08:35 pm
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Dear all,
Recently I used my KA3005D for battery charge process. I wasn't the best idea. After it, now finally when I switch on my KA3005D I got only 7,8V and 0A current. If I will set > 7,8V it stays the same 7,8V and 0A. Please help. I checked PCB, no visual broken parts.
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Have you removed front panel pcb? I think there is a diode, by the way is your model SMPS or with transformer and multiple AC windings?
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I attached few photos.
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pic2
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checked, it's fine.
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Soo... this thing is a Korad power supply, right?
Schematic: https://elektrotanya.com/korad_ka3005p_velleman_labps3005d_power_supply.zip/download.html
Confirm if this it the one for you device.
In PIC2 it looks like a bridge rectifier was very much overheated. And there seems to be corrosion/dirt/residue a bit everywhere. Confirm the bridge is still on the other side of the board and measures fine.
Are all voltages as expected?
- Transformer outputs 36VAC, 15VAC, 10VAC;
- DC regulated lines are +12VDC; -12VDC; +5VDC (in 2 different places because two 5V regulators) +3.3VDC. Double check the voltage over the 3 'big' 2200µF caps -> how much is it?
Have you measured the 7.8V on the output with a multimeter or is that what the displays tell you? Don't trust it, measure yourself and report please.
Most likely possibilities:
- Somehow the 36VAC from the transformer doesn't make it to the output anymore.
- The output transistors are dead (Q1 & Q2, driver is Q3 on the power board and this in turn is driven by Q4 on main board)
- Something is wrong with the analog/digital converter that measures the output and the CPU does not receive the correct information. (D6; U5A; U6A)
- Something is wrong with the D/A and the CPU can't set the output. In this case I would expect to still be able to set the value on the display (U5B; U6B; U7A; U7B and then Q4 and Q3)
Can you read the CPU model on the chip?
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Right KA3005D.
Transformer and it's voltages looks fine, like 45VAC, 18VAC, 10VAC (it's for communication board - not included). They are bit high. I have 245V in my room.
DC voltage +12, -12, 3,3VDC are ok. Please let me know where +5V regulators are located. I checked voltage on big cap(6800uF) is 35VDC.
7.8V checked on multimeter.
CPU model name is torn.
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Q1 & Q2, driver is Q3 on the power board and this in turn is driven by Q4 on main board
Have you checked these?
Check the schematic for the 5V regulators. There is one between the +12V and +3.3V. Don't know where it is, I've never seen that power supply myself.
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Q1 & Q2 were defective, Q3 and Q4 were fine. After Q1 & Q2 replacement PS is operating now. Thx for help.
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Good news, thanks for the feedback.