| Electronics > Repair |
| Korad KA3005P power supply faulty/repair |
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| cavlovic:
--- Quote from: mcinque on October 21, 2013, 06:49:23 pm --- --- Quote from: cavlovic on October 21, 2013, 05:40:26 pm ---Just a small update. Mine is too scrambled: --- End quote --- Sometimes who write a software use a local charset for the GUI and probably you're missing it. Maybe chinese? --- End quote --- Charset should be included with windows, but they maybe programmed it in previous versions and some charcode labels have changed in windows 7, that's why I'm getting those characters. I will install software on windows XP and check if it's the same. On the other note, I poked a little today through my power supply. They went through trouble of cleaning flux after soldering, but left a mess after cleaning: I cleaned all boards, and this should be the board, located in front part of PSU, where all the logic is happening: Current comes to the most right bottom connector from PCB on back of the power supply, where it's been rectified and smoothed, and exits to the front terminals from J2 connector. I checked all resistors with my mutimeter, and some of them, just up from those 4 caps, read much lower then their written values. Some 1Mohm read 10K, some 10K read 6K etc. Some of them seem fine. I believe those cause the problem with reading proper values, but just want to make sure with more experienced guys before I start desoldering and replacing those. For input protection there is a 1N5408 diode, 1000v 3A, which would not stop current from car battery when power supply is off. I guess I had it connected before turning output of the power supply ON. Here is back PCB with rectifier and pass transistors: Am I onto anything, or way off my path? :D Thank you all! |
| alm:
--- Quote from: cavlovic on October 22, 2013, 04:11:05 pm ---Charset should be included with windows, but they maybe programmed it in previous versions and some charcode labels have changed in windows 7, that's why I'm getting those characters. I will install software on windows XP and check if it's the same. --- End quote --- Locale settings may make a difference. It looks like the garbled labels are easy enough to guess, so it should be usable, though ugly. Third-party software is unlikely to support this power supply which is not very popular or emulating an established standard. Your choices are either using whatever crap the manufacturer gives you or writing it yourself, unless another user already did the latter. If their software is written in LABView, then they probably shipped LV drivers. If you own and are skilled in LV, then writing a better GUI would be fairly easy. --- Quote from: cavlovic on October 22, 2013, 04:11:05 pm ---I checked all resistors with my mutimeter, and some of them, just up from those 4 caps, read much lower then their written values. Some 1Mohm read 10K, some 10K read 6K etc. Some of them seem fine. I believe those cause the problem with reading proper values, but just want to make sure with more experienced guys before I start desoldering and replacing those. --- End quote --- Most likely other resistors in parallel. A 1 Mohm resistor is unlikely to go down in resistance to exactly 10 kohm. If you want to be sure, desolder and measure its resistance. I would rather figure out the circuit and measure voltages. Presumably a resistive voltage divider (possibly switchable if it has multiple ranges, those 74HC part might be analog switches), possibly a buffer amplifier (one of those SO-8 packages?) and then an ADC (probably built into that MCU with its part number sanded off). Ideally you would have values from a known good power supply to compare. I would be more suspicious of active devices, since resistors are less likely to be damaged by minor overloads. --- Quote from: cavlovic on October 22, 2013, 04:11:05 pm ---For input protection there is a 1N5408 diode, 1000v 3A, which would not stop current from car battery when power supply is off. I guess I had it connected before turning output of the power supply ON. --- End quote --- That's most likely an anti-parallel diode across the input, that does not protect against current flowing from the battery to the power supply. I was talking about a series diode between power supply and battery. |
| mcinque:
--- Quote from: cavlovic on October 22, 2013, 04:11:05 pm ---Charset should be included with windows --- End quote --- Afaik, european, u.s. or australian Windows does not have asians charsets installed by default. Maybe I'm wrong. --- Quote from: alm on October 22, 2013, 04:57:58 pm ---Locale settings may make a difference. --- End quote --- I agree. |
| alm:
I think there was another piece of crappy software from one of the Chinese test equipment manufacturers (Owon? Hantek? Rigol?) that had a similar issue. Edit: this may have been the post I was thinking about. |
| mos6502:
Is there another PCB in there with opamps? Because it doesn't look like there's analog regulation circuits on there. Could it be that the KA3005 uses the microcontroller to do the actual regulation? I looked at the Korad website, and the specs say that the transient response is 100ms. Yes, milliseconds! That's around 1000 times slower than a proper linear supply. Unless that's an error, that would indeed mean that the micro does the actual regulation. Which would be insane, and horrible, and make this supply all but useless except maybe for battery charging. I watched Dave's review and the steps in the voltage response would also point towards that. Anyone have a schematic for this piece of ... kit? |
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