Author Topic: Korad KA3005P power supply faulty/repair  (Read 85023 times)

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Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #50 on: January 28, 2014, 09:17:37 pm »
Ah. Found it. The fan wire wasn't routed through the slot in the fan housing and was then crushed when assembled, shorting to case/ground. What I saw on the scope was the PWM of the fan return,  pulled low by U12, an On Semiconductor  ULN2003A High Voltage, High Current Darlington Transistor Array. Splice or replace to repair.

A comment I saw on the video EEVblog #315 - Korad KA3005P Review/FAIL :

" The biggest problem with these 1HL brands is the counterfeit pass transistors. They can barely supply 1/3 their rated current due to a severely reduced SOA. I routinely buy them - they're a steal - and replace the pass transistors with the genuine parts. I never, EVER have problems again. I am very hard on power supplies and do everything I can to blow them up. "

Any thoughts if this mod is warranted? And details? If say, you are inclined to charge SLA batteries at 5 amps for a few hours which I would not be? Cavlovic killed his doing this I believe. Did you ever figure out how, or get a repair/replacement?

I wonder how hot the sink gets at a full dissipation. I don't have a thermocouple to check but will in a few weeks.

The overshoot isn't such a concern to me if it only happens at 3-5A load ranges as in Dave's video. Do you see that too, Bill?

All my voltage outputs are very accurate. I guess I like this PS for the money. Even if I have to fix it!

Allan
Did you look at my PDF of the schematic?  They are using three drivers for the fan, then two more for each relay, and one is spare.
 

Offline AllanMN

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Re: Korad KA3005P power supply faulty/repair
« Reply #51 on: January 29, 2014, 03:40:31 pm »
Yes, the overshoot does change depending on the load.  I do see overshoot at even low loads (although I don't remember what the loads were and what the overshoot was.. will have to try it again).

Ah. Well, that is a FAIL, and would be a thing to fix if it's very significant. Or at least know about. I haven't checked into that yet.

I was charging a 24V battery once, and drawing max current from the supply, and it did shut down due to over temp on the heatsink (or thermostat in the xfrmr... really don't know which tripped), but after a while of cool down (about 10 minutes), it powered back up ok.
It was running pretty hot and the thermal overtemp seemed to do it's job.

The heatsink is a little small if you are going to push it, and I may mod it with a larger heatsink (maybe even a larger fan), but for now it is working great for a cheapie!

I know alot of people whine about how cheap it is, and all it's problems, but like I have said, it ain't an HP/Agilent/Lambda/Fluke/etc., and I know that.

One thing on my supply... the FWB was NOT bolted to the heatsink and they relied on the stiff leads of the bridge!  It was NOT laying flat on the heatsink (the lead side was not touching the aluminum), so I desoldered the leads, bolted the bridge on the sink, and resoldered.  How cheap was that!
I would suggest that you check the mounting of the bridge to make sure that at least it is making good mechanical contact to the heatsink, and maybe even bolt it down... it probably runs pretty hot when under high load and will not last too long.

Here are some pics of the bridge (notice the slight space on the lead side), the xsistors and bridge (notice how the goop doesn't look like it was making contact on the bridge), and the contact area on the heatsink (only partial contact on the bridge).

Good to know. Yes, the sink is small, and maybe simple to improve. I might have some 1/8" Al sheet around to cut and bend up.

I'll definitely check the bridge when I replace the fan. Doug is sending me another to avoid splicing leads.

Seems colvinic (?) toasted his charging batteries and we haven't heard any more.

Quote from: pomonabill221
Did you look at my PDF of the schematic?  They are using three drivers for the fan, then two more for each relay, and one is spare.

Most definitely! That is a great contribution and I thank you for it!
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #52 on: January 29, 2014, 08:07:48 pm »
Did you think I had to splice the leads on the bridge?  I'm sorry I wasn't clear about that... there was enough lead length on the bridge (at least on mine), that I didn't have to extend or splice onto the leads....

Yes, the overshoot is surely something that I intend on looking into when I have a little more time.  Trying to rely on remembering to disconnect the output when switching on, or having to add a relay to the output (which I still may do for several reasons), doesn't fix the problem and I would like to fix the problem... just a personal "goal" or triumph!  hehe

I am glad that those of you that have downloaded my crude hand drawn schematics have found them useful.  I really tried to be accurate, but if you find something that isn't correct PLEASE let us all know!  OR if you have a question about my drawings, don't hesitate to ask!  (sometimes I have to ask MYSELF "what the heck did you mean by that??")

As crude as the software is, I still can't get it to work on my win7 64 box!  It keeps asking for matlab, and I don't have that!  And WHY would it need it anyway?  Just chalk it up to "crappy software"!  It would be nice though.
 

Offline commongrounder

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Re: Korad KA3005P power supply faulty/repair
« Reply #53 on: January 29, 2014, 09:32:03 pm »
@pomonabill221:

That's interesting about the software needing Matlab.  I'm wondering if the there is a runtime Matlab application embedded in the Korad software that isn't 64bit compatible.  If that were happening, when the program attempted to start it would not find the runtime app functioning and issue an error message.  Korad programmers may have used a Matlab core to build the graphing and analysis (as much as there is of it) portion of the program.  I spoke with my son, who is a programmer and has used Matlab.  He thinks you could look in the folder that contains the program files for the Korad software, and see if there are any files that are Matlab related.  There might be a 64 bit version available that could be put in place to fix the problem.
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #54 on: January 30, 2014, 12:10:04 am »
HHmmm.. that could be what is going on!
I will take a look and see.
thank You.
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #55 on: January 30, 2014, 12:40:28 am »
WOOPS!!!  I meant labview... sorry
This is the error that pops up when I start the app,or try and run a program.
I can't find any kind of .ini file that would have the save path (it defaults to D:\ka3005p save data\  but I can't change it!)
It is controlling the supply, but I can't do what I want to (run a program).
Frustrating!
 

Offline AllanMN

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Re: Korad KA3005P power supply faulty/repair
« Reply #56 on: January 30, 2014, 07:42:10 pm »
Did you think I had to splice the leads on the bridge?  I'm sorry I wasn't clear about that... there was enough lead length on the bridge (at least on mine), that I didn't have to extend or splice onto the leads....

Huh? No, sorry, I meant the fan lead which was crushed and shorted to ground/case, and almost severed. It's very fine wire, stranded, and I find those can be hard to splice when they are like a few fine hairs.

 

Offline AllanMN

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Re: Korad KA3005P power supply faulty/repair
« Reply #57 on: January 30, 2014, 07:50:26 pm »
WOOPS!!!  I meant labview... sorry
This is the error that pops up when I start the app,or try and run a program.
...

Often there is some kind of free runtime software for developed applications you need. Perhaps this?

http://www.ni.com/download/labview-run-time-engine-2013/4061/en/

Might be worth a quick try. I'll try it on XP and see if I can shed light on it sometime here.

Allan

 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #58 on: January 31, 2014, 01:12:10 am »
Did you think I had to splice the leads on the bridge?  I'm sorry I wasn't clear about that... there was enough lead length on the bridge (at least on mine), that I didn't have to extend or splice onto the leads....

Huh? No, sorry, I meant the fan lead which was crushed and shorted to ground/case, and almost severed. It's very fine wire, stranded, and I find those can be hard to splice when they are like a few fine hairs.
OH ok... yes I agree the fan wires are small.  Lucky you found the problem and it was easy to fix!
Does the fan speed change with different loads (it will only change from idle with a load).  Normally it just idles.
Just curious to make sure the fan driver isn't cooked.
 

Offline AllanMN

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Re: Korad KA3005P power supply faulty/repair
« Reply #59 on: January 31, 2014, 04:52:08 pm »

Does the fan speed change with different loads (it will only change from idle with a load).  Normally it just idles.
Just curious to make sure the fan driver isn't cooked.

Yes, all seems well. I only briefly connected negative to ground once I saw a malfunction, fearing doing damage.
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #60 on: February 01, 2014, 05:33:02 pm »
IF the supply is floating (which it should be), you should be able to ground (connect to earth) either the positive or negative output.
This is a common way to obtain a negative voltage referenced to ground (earth).
I know that sometimes ground and negative are interchanged, but in this case I am referring to earth as ground.

Great that your supply is working!
Just remember that it does have it's inherent problems (like spiking on power on, a slight overshoot when the output is turned on (could damage what you have connected)).
If you have a scope, take a look at the output to verify these symptoms... and remember it IS a cheapy chinese product, but I like it and I could afford it.
 

Offline tony3d

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Re: Korad KA3005P power supply faulty/repair
« Reply #61 on: February 01, 2014, 05:56:27 pm »
I have been using mine for months now with no issues at all. I wouldn't leave it unattended pushing 4 amps, but anything under an amp or so I feel very confident with.
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #62 on: February 01, 2014, 07:30:02 pm »
I agree with not leaving it unattended pushing high current, but it's over temp seems to work pretty good (I found out), and I would feel safe at about 3 amps max., just watch the temps and feel the fan's output air temp.
Still.... it's not a bad idea to be around while it is powering something, just to be sure!
 

Offline AllanMN

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Re: Korad KA3005P power supply faulty/repair
« Reply #63 on: February 05, 2014, 06:40:46 pm »
Here are some pics of the bridge (notice the slight space on the lead side), the xsistors and bridge (notice how the goop doesn't look like it was making contact on the bridge), and the contact area on the heatsink (only partial contact on the bridge).

Mine had a bolt tightened through the bridge and it was tight. Like my crushed wire, assembly has many errors without QC to catch it.

 

Offline commongrounder

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Re: Korad KA3005P power supply faulty/repair
« Reply #64 on: February 06, 2014, 02:51:51 pm »
After reading about AllanMNs experience with a trapped wire, I figured I had better take a look inside mine to see how it faired the assembly process.  Mine did pretty well.  I found a couple of loose screws on the power transformer (mine is the dual supply, and the xformer is huge and heavy).  I also found the regulator board for the fixed 5-volt supply had a screw missing, which I replaced.  Here is something interesting.  I can see the area where the I/O connections are made, but mine is not a USB/RS232 version.  However, the circuit board is sitting right there, half populated.  Even the opto-isolators are there.  I wonder, if there were a way to determine what chips are used, whether my unit could be converted to have I/O capabilities.  If someone were willing to post a photo of that board that has the I/O connectors and related circuitry, I might be able to create a parts list for the conversion (assuming the parts have visible labels).   I could also post a photo of my partially loaded board for comparison.
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #65 on: February 10, 2014, 12:36:23 am »
Wonder if the firmware is the same for all the models?  For instance, if you were to populate the I/O board, would the supply recognize commands?
If it isn't alot of trouble, might be worth trying it out!
 

Offline commongrounder

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Re: Korad KA3005P power supply faulty/repair
« Reply #66 on: February 10, 2014, 02:13:38 pm »
Yes, I'm curious about the firmware compatibility, as well.  If I can ID the parts, I might try it just to see what would happen.  It would be fairly low risk and wouldn't take much time to set up.  I could also see how much the I/O board would cost as a part and just swap it out.
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #67 on: February 11, 2014, 10:14:07 pm »
Here are some pics of the I/O board.
 

Offline commongrounder

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Re: Korad KA3005P power supply faulty/repair
« Reply #68 on: February 11, 2014, 10:35:05 pm »
Fantastic, pomonabill221!   ;D  Thank you very much for taking the time to do this.  I will study these and see if I can come up with a parts list for completing an I/O mod for a non-USB/RS-232 Korad.
 

Offline commongrounder

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Re: Korad KA3005P power supply faulty/repair
« Reply #69 on: February 12, 2014, 06:50:51 pm »
Okay.  I studied pomonabill221's photos and pulled my board.  Surprise!  :palm:  The boards are not the same...  I am assuming there is either more than one version of this board, or there is a board designed specifically for the KA300xD or P-3S triple output supplies.  I've attached a photo of my board.  If anyone has a "P" version of the triple output supply with the populated I/O board they feel like sharing a photo of, I will research the missing parts.  Thanks!
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #70 on: February 12, 2014, 09:13:57 pm »
Okay.  I studied pomonabill221's photos and pulled my board.  Surprise!  :palm:  The boards are not the same...  I am assuming there is either more than one version of this board, or there is a board designed specifically for the KA300xD or P-3S triple output supplies.  I've attached a photo of my board.  If anyone has a "P" version of the triple output supply with the populated I/O board they feel like sharing a photo of, I will research the missing parts.  Thanks!
DANG IT!!!  Sorry yours is different.  I hope you find someone that has the info for you!
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #71 on: February 12, 2014, 09:19:14 pm »
Okay.  I studied pomonabill221's photos and pulled my board.  Surprise!  :palm:  The boards are not the same...  I am assuming there is either more than one version of this board, or there is a board designed specifically for the KA300xD or P-3S triple output supplies.  I've attached a photo of my board.  If anyone has a "P" version of the triple output supply with the populated I/O board they feel like sharing a photo of, I will research the missing parts.  Thanks!
I betch ya that U 2_2_1_1 is the max232 uart.
Can you trace the pins from the USB/DB9 connector?  Where do they go?
Just assuming that the second flat pack isn't used?  Just a general observation on what IS there is that the vacant parts around that chip are not used.
It almost looks like the two controllers talk to each other, or share common data/address lines.  hhmmmm....
What's with that crystal being mounted diagonally???  Strange!

You really need to see someone else's board though... hopefully the second flat pack isn't used!
Good luck!
« Last Edit: February 12, 2014, 09:24:15 pm by pomonabill221 »
 

Offline commongrounder

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Re: Korad KA3005P power supply faulty/repair
« Reply #72 on: February 13, 2014, 03:23:54 pm »
Thanks pomonabill221.  I will do some tracing out of the board when I don't need to use the supply for my work.  It may well be possible to figure out some of the parts by context.  As concerns that crooked crystal, they chose to mount it on the board up on its legs rather than directly on the surface.  It is just twisted a bit on its legs.
With any luck someone might see this and do a quick photo.
 

Offline pomonabill221

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Re: Korad KA3005P power supply faulty/repair
« Reply #73 on: February 13, 2014, 08:14:46 pm »
I'm toying with the idea to replace ALL the output stage (three transistors/diodes/ballasting resistors/base resistors) with a single power fet, driven directly from the control board.

With a fet, you don't have thermal runaway and at least I know that it IS a real fet and not a counterfeit look alike!
I really don't like the use of ballasting resistors although with transistors it is necessary.  Even with several parallel fets though, you don't need ballasts as the fets will self ballast.

I'll give it a try and see what happens.
 

Offline jldesigns.eu

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Re: Korad KA3005P power supply faulty/repair
« Reply #74 on: April 29, 2014, 11:04:44 am »
Hello Folks, Since this is my first post on the EEVBLOG forum wanted to say Hi to ALL :)

I was a happy owner of Korad KA3005D-3S, until left half of my power supply failed. During testing of a system (12V 2A), cracking sound burning smell and smoke came out of vent holes.

Its only been used few times since I've bought it 13 months ago but distributor refused a warranty service (12 months warranty).

Since I’m electronics engineer I’ve turn it apart and fund that the microprocessor board has malfunction caused by fan short circuit (or possibly other way around). ULN2003A was blown, I’ve replaced the fan and ULN, to find out that 3 op amps are also shorted (TL082C), replaced those but that was not the end. There was something still short-circuiting 3.3V line, found out that it’s a microprocessor with sanded markings.

Can you help me in any way with fixing my PSU? I would need:
- a programmed microprocessor (probobly wont get it) or
- full microprocessor board (maybe Korad sells replacements?) or
- a firmware for the uC (second board from other half of my PSU is ok, but i doubt Korad didn't lock the firmware) or
- i could possibly write my own firmware, but reverse engineer the board would be a nightmare

Thanks in advance for any support.

PS. On the attached photo the board have desoldered 3.3 LDO and a ceramic cap on it, it was to check what is shorting out 3.3V line.
 


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