EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Pythzepf on March 09, 2016, 10:34:27 am
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Hello!
I recently purchased a KORAD KA3005D. I have had it for about a month and have hardly used it. The last time I used it I tested its maximum output (just playing around) by shorting crocodile leads at 31V 5A. It did well, wires got hot. I did not keep it on long, 30 seconds tops.
I plugged it in today and this is what happens:
1) Pressing the button sends an inductive spike into the mains (lights flicker)
2) the device turns on, all is good
3) Cooling fan hits max rpm (loud)
4) Voltage and current can be dialed, memory settings selected, but there is nothing on the output when "On/Off" button is pressed. More specifically: when output is switched on, dials show 0 V 0 A instead of a dialed 5 V (example) 0 A (nothing connected).
Are there any ideas before I open her up? I did read from this https://www.eevblog.com/forum/repair/korad-ka3005p-power-supply-calibration/25/ (https://www.eevblog.com/forum/repair/korad-ka3005p-power-supply-calibration/25/) thread that the power transistor block on a KA3005P was not really making contact with the heatsink (reply nr. #49). Could it be eg. pass transistor fail from overload?
Sincerely,
P.
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Why can't you return it under guarantee ?
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Hi,
to me it sounds like either a loose connection that got burned out or a dead output transistor. But one fact bothers me. It's the Fan that is running at full speed, because it is normally linked directly to the measured output current. If your supply is still under warranty you might send it back to where you bought it from, as newer board versions are much more robust! :)
Regards,
Dachpappe
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I probably should send it back, shouldn't I. It is such a hassle though. It was shipped from Hong-Kong (!) to Europe and the customs are in the way, plus a ton of time (I bet two months there and back again). I needed it today :) I'll contact the seller and see if they can just replace it.
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Burned?
https://www.youtube.com/watch?v=nmLQ_Qh8INg (https://www.youtube.com/watch?v=nmLQ_Qh8INg)
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isnt that the same piece of crap Dave burned during a review? you were warned and still bought shit
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https://youtu.be/Fya-4mjV4N4?t=23m39s (https://youtu.be/Fya-4mjV4N4?t=23m39s)
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Well, I opened it up, and all the output checked OK. It was actually a pretty lame problem: a loose low voltage transformer output. Might have had something to do with the silicone (or whatever stuff it is) they put on all connectors. It was probably semi loose to start with.
Cheers,
P
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It looks like you made the right decision, to try and fix it. Which saved you from a lot of hassle.
The fault you described, makes the power supply sound like it has been made with little care, quality or design flare. You have at least confirmed the reliability of Dave's video(s) about it.
At least it is a linear PSU, which should make any future repairs, somewhat easier.
Congratulations in sorting your problem out, anyway.
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I got one of those cheapy supplies from a vendor "for parts" and the transformer was loose. It had torn the wire right out of the paper wrap of the transformer. This winding supplied power to the floating digital display. If one knows what they are doing it is advisable to open up equipment that has had a lot of shipping. Can't say the same thing for deliberately shorting out new equipment just to see what it will do.
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I bought the TENMA 72-10495 (AKA Korad KA3005D-2S) dual channel power supply, but there are many issues with it. To help others understand it's limitations before buying it (or to help work out its insane user interface after purchase),
here is the manual, marked up with corrections and warnings about bugs in the user interface and behaviour:
https://ufile.io/drsjx09j
This applies to models:
- TENMA 72-10495 (Korad KA3005D-2S): 30V-5A x 2 Channels
- TENMA 72-10500 (Korad KA3003D-2S): 30V-3A x 2 Channels
and probably also
- TENMA 72-10505 (Korad KA3003D-3S): 30V-3A x 2 Channels & 5V-3A x 1
Important notes to avoid damage:
● Do not allow power supply to sink current. Use diode when charging battery.
● For sensitive circuits, see Avoiding overshoot and excessive in-rush current :
○ Inside the power supply, there is a capacitor near the output terminals for stability. The current limiting and over current
protection (OCP) cannot control current from this capacitor.
○ There is some overshoot on turning a channel on.
○ There is a spike when turning mains off while the channel is on.
● In parallel mode, connect load to CH2 (right hand) channel. (When mains power is turned on, the power supply defaults to
independent mode, and CH1 to whatever voltage and current settings are in CH1 memory recall M1, with the load turned off.
Therefore, avoiding CH1 could prevent mistakenly applying wrong settings to the load.)
● OCP and OVP do not work in serial and parallel modes.
● If you recall a CH2 memory in SER mode, only CH2 is updated from that memory and only CH2 turns off. At this time, CH2
output terminals have up to -1.2 V (i.e. reverse polarity) on them, with a short circuit current of up to -2.8 A.
This also happens when the channels are independent but you have wired them in series.
● When using the power supply in SER mode, or wired in series, you may have to ensure the supply is working in CV mode to
avoid instability.
Important notes to avoid confusion:
● There is a small negative voltage and current when the load is switched off (50mV, 100 uA)
● OCP/OVP:
○ CH2 OUT LED stays on after CH2 OCP/OVP trip disconnects the load.
○ OCP and OVP do not work in serial and parallel modes
○ CH2 OVP/OCP buttons also control CH1 OVP/OCP
○ CH1 OVP/OCP buttons only control CH1 OVP/OCP
○ The OCP and OVP LEDs apply to whichever channel last updated them. Pressing either the OVP or OCP button updates both the
OVP and OCP LEDs with that single button push.
● An OCP/OVP trip for one channel does not trip the other channel
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aka buy a different power supply :-DD