KA3005D fail - Page 1
Forum section: electronics / repair

author: king
author_rank: Newbie
timestamp: April 06, 2023, 08:08:35 pm
content: 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.

author: philo
author_rank: Newbie
timestamp: April 07, 2023, 12:41:23 am
content: 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?

author: king
author_rank: Newbie
timestamp: April 07, 2023, 10:11:36 am
content: I attached few photos.

author: king
author_rank: Newbie
timestamp: April 07, 2023, 10:19:49 am
content: pic2

author: king
author_rank: Newbie
timestamp: April 07, 2023, 10:38:55 am
content: checked, it's fine.

author: Swake
author_rank: Frequent Contributor
timestamp: April 07, 2023, 01:40:01 pm
content: Soo... this thing is a Korad power supply, right?Schematic:https://elektrotanya.com/korad_ka3005p_velleman_labps3005d_power_supply.zip/download.htmlConfirm 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?

author: king
author_rank: Newbie
timestamp: April 07, 2023, 04:23:40 pm
content: 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.

author: Swake
author_rank: Frequent Contributor
timestamp: April 07, 2023, 05:47:19 pm
content: Quote from: Swake on April 07, 2023, 01:40:01 pmHave 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.

author: king
author_rank: Newbie
timestamp: April 12, 2023, 04:57:21 pm
content: Q1 & Q2 were defective, Q3 and Q4 were fine. After Q1 & Q2 replacement PS is operating now. Thx for help.

author: Swake
author_rank: Frequent Contributor
timestamp: April 13, 2023, 11:38:18 am
content: Good news, thanks for the feedback.