Korad KA3005P power supply faulty/repair

[mos6502]

Hey, at least something  Now you only have to program your own firmware and redesign the regulation circuitry. 

[Kleinstein]

Having something like 330 µF at the output of a lab power supply is about normal. There are supplies with even more capacitance at the output, that are still considered good. A normal lab supply is not expected to be very fast in regulation, as this makes is really difficult to have it stable with any possible load. There is also not much sense in making the supply faster than 1 m of cables. So if you have a load that needs fast current spikes, add local decoupling capacitors.  There are also PS designs that have way less capacitance at the output, but still have a poor / slow current limiting and may this way behave as if there would be an even larger capacitor.

The funny high frequency transients look a little strange. So the question really is how much of this is at the output terminals and how much is just EMI coupled to the wires to the scope.

[mos6502]

I disagree, 330µF is way too much. My TTI PL320 has 47µF and you can still kill a zener diode if you're not careful and dial down the voltage far enough. 330µF will fry a lot of stuff if there's a fault in your circuit.

I'm not quite sure what you mean by "faster than 1m of cables". But a proper bench PSU will have separate sense connections to compensate for any lead resistance. So yes, fast regulation/low output capacitance are what makes a bench PSU useful.

In the case of the Korad, you might as well buy a switching power supply like the CPS3205. It's smaller, lighter, cheaper and more efficient.

[pomonabill221]

Way back in the thread somebody posted reverse engineered schematics...

I have found some better schematics for the device. And as the support for the device is far from being called 'support', I think this must be here. Attaching to the message. Maybe someone will stick it up to some 'documents' theme.

Well my efforts were for not then?
Thanks for posting the schematics!
Finally after 4 years,, we have complete schematics!

[uv3afl]

Well my efforts were for not then?

I shouldn't say so! If you look closer to the schematics you will notice some annoying mistakes. For e.g. at main board two 'GNDF' at upper of R13. Looks obviously confusing.  And here I take your sheet and set everything into places  I'm too lazy to take CAD and draw everything like it shold be. By the way, good moment to say thanks for your rev-eng job! It was first internals info about this PS that I've seen!

[basil]

I am having a strange problem with my KORAD 6005D (60 V 5A model ) !!!!
-> Power supply works perfect up to a set voltage of 19V ~ 20V .
-> If i increased the set voltage above ( ~21 till 60) & (o/p is enabled ) , i can hear a relay tick sound from the power board at a constant interval . At this time i am getting a voltage discharge ramp at the output terminal . In the front panel display values also i can see this effect ( display works good )
-> i noticed that , If i remove the voltage feedback/sense line from the connector J10 at the front panel pcb the relay ticking stops ( but the power suppy will not work as the sense lines are removed , right ? )

I can share more specific details , If someone can help me to figure out the issue .
 

[Kleinstein]

The description somewhat sounds like a problem with transformer tap switching. Maybe a worn out relay contact or a loose wire / blown fuse from the transformer. My guess is that the higher transformer tap for some reason does not deliver power.

The 60V 5A version is likely different from the smaller units in some aspects. I would expect a different transformer tap switching at least, to reduce power loss. So a little more information, a few photos of the internals might help. A visual inspection for lose wires, maybe cold solder joints or blown fuses would be the nest step anyway.

A helpful point to measure would be the voltage of the large filter cap (e.g. solder temporary wires and measure). It needs some care: the voltage could go to about 80 V and in case of a short there is plenty of power.

[basil]

 You were absolutely right and thank you very much for the inputs  !!!

 It was due to a faulty relay ( K3 in my case ) . Now the unit is working perfect . 

[uv3afl]

Hey, at least something  Now you only have to program your own firmware and redesign the regulation circuitry. 

Yes, KA3005P is really 'at least something'. And no DIY with it! It's not interesting, because it's somewhat classic )) It's a cheapie with more than reasonable functionalyty for it's cost.
And here is the PS of my real interest that I build now. Fortunately, it's completely open source and there's no need to develop something from scratch. And I am almost done with it. It works fine but there's still some mechanical work to fit it into the case. By the way it has no cap on output terminals inside by default. It is really fast in regulation and offers LED operations with current limiting. But... there's the other side - on some loads people catch some oscillations. And... Put some output cap on terminals 

[Tony Mach]

So I have a faulty KA3005D… and maybe someone finds the information helpful I have gathered so far (unfortunately I am not done yet).

Pinning down the problems with my PSU

At my workplace we bought this PSU, and it was broken out of the box. You could press OUTPUT, but it would not output anything… The voltage would stay at 00.00 V and the current at 0.000 A. Otherwise it seemed fine.

From time to time one or the other colleague took it, played around with it, couldn't accomplish anything, and then put the PSU angrily back into the shelf…

Now I had enough and declared the PSU dead – but I didn't want to give up so easily. Instead of having to put the PSU in the electronics-dumpster I was allowed to take it home. And now it is my problem…

With the help of the schematics here I did find out that the power-board (in the rear) is fine. With a voltage on pin 1 I could change the output voltage. The 7-segment displays even displayed the output voltage and current! The problem seems to be localized on the control-board (the MCU, the two discrete DACs with the comparators).

With the "calibrate" procedure I could find out that the "zero voltage" is adjustable from about -100 mV to about +200 mV in steps of about 2 mV. The three other calibration settings ("zero current", "max voltage" and "max current") do nothing (sometimes the voltage "blips" when turning the wheel). While I can not rule out a hardware problem, I suspect a software problem. (Maybe wrong values in the I2C-EEPROM?)

Going after the Firmware

Somewhere I found out that it is a Nuvoton M054 MCU. And oh wonder of wonders, at my workplace we have a Nuvoton Nu-Link-Me. I managed to connect it (see attached image), and I could connect to the MCU right away! In my PSU there is a M054LDN. Success! But no, not so fast, unfortunately the "security lock" for the flash is enabled – so I can not read out the firmware and can not debug it. At least I was able to get a PinView which I attached as a screenshot (whether it is accurate is another question).

So I could write my own firmware…

Next step: Getting into CooCox with the Nuvoton MCU.

Famous last words: How hard can it be to manage a handful of GPIOs?

So that is what I have so far. I don't promise that I will be able to follow up on that. Maybe I will, maybe not, or maybe someone else can use that information.

[Kleinstein]

It depends on the hardware and desired functions how complicated it would get wirting your own software. The main part could very well be interfacing the LCD output. Controlling the DAC / ADC should be relatively straight forward, unless they used the µC and a few external parts to implement a kind of high resolution sigma delta of other integrating ADC. Before deciding on the software, one should have a better picture on the actual hardware to control.

AFIAK there is a chain of 74HC(T)595 used as a shift register for a R2R type DAC. So one might be a able to check the serial signal - just in case the trouble is not with the MCU. One could also check just the output of the R2R chain - this should be relatively easy to identify on the board.

Edit:
Looks like there are schematics available. No more than just the DAC, even the ADCs and display seem to be external. So if really needed, the software would be relatively simple. It would really worth looking at the DACs output, to exclude a problem with the control OPs.

[Andreas]

Hello Tony,

is the output relay clicking when you activate the output?

With best regards

Andreas

[Tony Mach]

@Andreas:

This is a economic PSU, it has no relay for the output. Very economic. (One more reason I would want to write my own software, to add a relay for the output… the control-board even has an output for such a relay.)

@Kleinstein:

I have no isolation transformer, and the mains-switch is on the frontpanel – very near to the R2R DAC …

I am so tempted to write my own software (even if this PSU has an hardware fault – it would be easier to pin down the fault if I know what I output).

The main task would be to learn how to I/O on a Nuvoton with CooCox (there is some support in CooCox, but I'm an AVR32 guy, and everything in this new world feels slightly strange…)

Otherwise the tasks would be:
- Setting of the DAC (outputting with the 7495s)
- Output via LEDs (as well 7495s)
- Input of the wheel (interrupts?) and buttons (button matrix?)
- General "user interface"
- Reading the ADC for the voltage and current
- Switching the relays for the windings (voltage "preselect")
- Overcurrent handling
- Some calibration routines
- Reading/writing to the I2C EEPROM

Other niceties (which can wait) include:
- Reading the temperature and adjusting the fan
- Buzzer
- Output Relay
- Use of M5 LED to display "LOCKED"
- I/O via serial interface
…

Yeah, very doable. 



I just need to get started…

 

[Kleinstein]

If you don't won't to poke around the circuit when life, one can usually solder wires to the test-points and connect everything to a DMM / scope before powering up.

If the mains switch is so close to the logic part, one should consider insulation (e.g. heat shrink or similar) anyway.

The µC is supposed to be ARM M0 based. AFAIK it takes some time to get used to the a new type of µC. A first point would be to decide on what type of support files (e.g. HW definitions as C include files) to use. Often there are kind of higher level version with special macros for initialization - however some of these systems are controversial. So some use the higher level interface and some only the register names. The biggest part is likely getting started to get a first program.

[Tony Mach]

Every solder point I touch brings a PCB closer to death… I'm more a software person… So I'm glad the debug connection is working.

Anyway, I got a "hello world" to compile in CooCox for the M054 with setting of one GPIO (for the fan).

So after I successfully compiled, I could not resist, and the original firmware is already GOOOONNNE !!!

The first I did was to switch the fan (P4.1) between full speed and low speed, which was surprisingly easy.

I just added the switch of the columns (P1.4-P1.6 and P4.2) of the LEDs.

I am making unreasonably fast progress… I smell a trap. 

Next I have a date with the 7495 shift registers – something I have been looking forward to do long before I met the Korad PSU.

[Andreas]

This is a economic PSU, it has no relay for the output. Very economic. (One more reason I would want to write my own software, to add a relay for the output… the control-board even has an output for such a relay.)

Hello,

I have 4 of the units (2 * KA3005D and  2*KA3005P).
All 4 have a output relay.

So either you have a KD3005 or something is wrong.

With best regards

Andreas

[Tony Mach]

Well, I definitely have a KA3005D, and no output relay.

Please be advised, there are (at least) 3 version:
- The "old" version, that eevblog initially tested (only one capacitor on the power-PCB)
- The "middle" version, with updated PCBs (three capacitors on the power-PCB)
- The "new" version which has among other changes "screw type" connectors for the output (the old/middle had "plug only" connectors for the output)

I have the "middle" version. It has 2 relays for switching of the windings, but no output relay.

Meanwhile, I now have a first version of my software that can access the two DACs (for voltage and current), and I can switch the output voltage in software – while I have not figured the DACs out completely (and might still have a bug or two), I think the hardware should be OK. This must have been a configuration problem.

Achievement unlocked: 74HC595
Achievement unlocked: Control the seven segment display
Achievement unlocked: Control the DACs

As I can get voltage and current out of the PSU, if I either manually set the control voltage, or if I set the DACs in software – without switching any relays in both cases – I am quite certain that there is no output relay in my KA3005D. I even looked and visually checked all the PCBs – I did find only the 2 relays for the windings on the rear PCB, there is no output relay in the path.

I am curious: Where is this output-relay in your PSUs? On the power-PCB? Or on that little connector-PCB? On the main-PCB?

Anyway, my software needs further work… Once more onto the breach!

[Andreas]

Ok you are right,

the clicking that I hear is from the transformer switching when I set the voltage above 5V.
(What I usally do).

With best regards

Andreas

[Tony Mach]

Hello Andreas,

when you go above 5V, you hear one of the "windings relays"! Both winding relay are connected in such a way that there is always a connection from the transformer to the power electronics.

The only thing that selects an output of 0 Volt is the control voltage. If this control voltage fails (e.g. faulty DAC), or if the winding relay fail (happened to one person, there is a video on youtube), you will get voltage on the output.

Unfortunately there is no output relay.

Kindest regards.
Tony

Anyway, I made further progress!

The SHCP and STCP are mislabel on the processor end…    I spend at least 2 hours trying to figure out why my 74HC595 routine did not quite work with the DACs 75HC595s… The same routine worked just fine with the LEDs 75HC595.  They mislabelled these two pins on the schematic… 

But now I can control the DACs!!! 

Achievement unlocked: Output hexadecimal numbers on the LEDs
Achievement unlocked: Control the DACs

Onwards to success! 

[Tony Mach]

Well, I reached a crucial point with my firmware for my KA3005: The basic functionality (and everything needed for this) is working!!! I can adjust voltage and current, and the respective values are displayed! 

It took a little longer than I thought to reach this point – but hey, I do this in my spare time, for free and for fun (at least my tortured sense of fun)…

There is a metric ton of caveats attached to this firmware:

• This works on my KA3005 - other hardware revisions may have critical differences (There is much strangeness in the schematic…)
• AFAIK one can not read out the original firmware - so once you overwrite the original firmware you can not go back
• There is no calibration routine, the calibration values are hardcoded
• CooCox and the debugger are strange… Relays sometimes switch when you load new firmware – this contributed to me having once shot the power transistors  The firmware was broken, so I wrote a new firmware, which broke the PSU - talk about irony… (But hey, I bought new transistors, fixed it  and learned an important lesson: Do not leave a load like a 12V 100W bulb attached when the debugger is attached - detach any bigger electrical load before you load a new firmware. A 230V 50W bulb on the other hand is fine.)
• I make mistakes (I once reached a peak value late at night of 2 bugs per 1 line of code) – this also contributed to the aforementioned incident where I shot the power transistors  But now the switching of the relays should be solid.
• Memory is not implemented (M1 to M5 not done)
• The interface to USB/serial is not implemented (my PSU model is without the interface board, and one would need to reverse-engineer the protocol, so this maybe will never happen)
• The keys are not debounced
• No LOCK, no OVP, no OCP
• The LEDs flicker under certain conditions (I know how to fix that, but haven't had the time to do it…)
• Haven't fully figured out the temperature-ADC yet
• Fan is switched on with the output, and runs aways with full speed while output is on
• Other problems I forgot
• Source code needs clean-up
• No warranties whatsoever
• No buzzer

But there are also good things:

• No buzzer
• IMHO the adjustment of voltage and of the current is nicer in my firmware (and I might improve it even further by a little bit)
• Considering the power rating of the transformer, and of the transistors, I think it could be possible in future to "overdrive" the PSU and output more voltage, or possibly even more current, under certain circumstances (if one stays within the ratings of those components)
• One could implement custom behaviour (e.g. "soft start", or specialized battery charger, or or or …)
• One could add an output relay, or maybe even an MOSFET as an output switch

If you want to use this firmware, you need CooCox (I used 2.0.7, but other versions should do fine). I had to add cmsis_core, M051_BSP_CMSIS_V300_001 and C_library to my project (the C_library might not be necessary - the boilerplate I used needed it, but I haven't checked if I still need it).

Sorry, no pre-compiled binary from me, no turn-key project – if you want to use this experimental firmware, you need to know what you are doing. Have fun tinkering! 

I might continue working on some of the missing features, but I do not promise anything. 

[xani]

I guess lessons learned here is that if you even design a power supply, make sure it is is safe even *if* your MCU outputs "please emit smoke" combination

I guess I'm lucky that only problem with my KA3005D-3S (not produced anymore, it is like 2 KA3005D glued together + 5V 3A output + option to link two to get 60V or 6A) was dodgy power switch (locked in place) and a bit loud fan

[rufusalceste]

Hi Folks,

I am currently trying to repair my Tenma 72-10495 (rebranded KORAD psu) . I found the issue but I would like to replace R3 and R4 on both outputs boards as these have heated a lot and burned some of the PCB right under them. I am afraid their value is now off...
The problem is I can't manage to figure the value of these resistors (see photo attached) as the colors are pretty unclear and also because this kind of color arrangement (low value resistor ?) is new to me.
R3 seems to be black/black/silver (or is it brown/black/silver ?)
and R4 seems to be black/black/gold (or is it brown/black/gold ?)

The picture is pretty representative of what I can see with my own eyes.

If any one of you guys has a clue that would be great.

Thanks a lot !

[Armadillo]

Hi Folks,

I am currently trying to repair my Tenma 72-10495 (rebranded KORAD psu) . I found the issue but I would like to replace R3 and R4 on both outputs boards as these have heated a lot and burned some of the PCB right under them. I am afraid their value is now off...
The problem is I can't manage to figure the value of these resistors (see photo attached) as the colors are pretty unclear and also because this kind of color arrangement (low value resistor ?) is new to me.
R3 seems to be black/black/silver (or is it brown/black/silver ?)
and R4 seems to be black/black/gold (or is it brown/black/gold ?)

The picture is pretty representative of what I can see with my own eyes.

If any one of you guys has a clue that would be great.

Thanks a lot !

R1 = 1Kohm  5W
R3 = 0.1 ohm 2W
R4 = 0.1 ohm 2W

[Andreas]

Hmm,

in the cirquit diagram attached here:
https://www.eevblog.com/forum/repair/korad-ka3005p-power-supply-calibration/msg370823/#msg370823

R3,R4 are 0.22 Ohms.

So could it also be red,red,gold?
Or have the values changed over the years.

with best regards

Andreas

[rufusalceste]

Thanks a lot guys.

Found more info in Dave's followup video on the Korad PSU.
Seems the older version (yellow PCB) had 0.1R resistors and the newer version (green pcb ) has 0.22R resistors.
See screen grab below.

Cheers !