Author Topic: Takasago KX-210 power supply  (Read 3535 times)

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Offline blueskull

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Re: Takasago KX-210 power supply
« Reply #25 on: February 02, 2018, 05:40:28 am »
What is the function of RL1 in this circuit? I found the data for this component:

NTC R68 limits inrush current. After initial inrush, RL1 turns on to bypass R68 to reduce I2R loss.
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #26 on: February 05, 2018, 05:15:05 am »
Today I started on the sub-power board. This has leads coming in from the rectified unfiltered high voltage DC from the main power board I showed last time, which come in through the black and white twisted leads at the bottom of the photo of the board, and then it has its own switching power supplies on this board, which go to, for example, the fan, which runs on 24V DC and was not working when the unit was switched on initially.

I spent some time tracing out the high power leads on the reverse of the board, and I noticed an odd phenomenon with this board where there was a quite big track leading to the large transformer which looks like it should be carrying power to or from the transformer, yet the bottom lead of the transformer, circled in pink on the attached photograph, has no continuity with any of the other transformer leads.

After looking at the transformer, one thin piece of enamel wire on the leads has snapped. You can see in the photograph below. Although it is difficult to see in this photograph, the backlit enamel wire which seems to have snapped is the same type of wire as the wire on the right of the transformer, and then the thicker enamel wire on the left side of the transformer also has a pair opposite the apparently broken wire which is just visible in the photograph coming round the plastic box, so it's not connected to that wire.

It seems likely that the wire was broken in a shock of some kind, or perhaps overheated, and the way to fix this is to desolder the transformer then put a jumper over the broken wire.

(Unfortunately, after a lot of effort, this was the best photograph I could take of the broken wire, since my camera will not focus on small items.)

« Last Edit: February 05, 2018, 05:30:54 am by Asuka »
 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #27 on: February 05, 2018, 06:25:45 am »
You will need to have the auxiliary power supply working, otherwise the unit will appear dead. I think you should concentrate on here as the priority.
The big cap looks like it bulk on the top [maybe camera effect]. I suggest you take it out and measure the ESR. Don't measure in circuit. I would say never for suspected cap.
If you suspect the transformer, then take it out of the board to inspect it closer and measure its primary and secondary inductance as well as continuity test. I have never seen transformer wire "burn" like this.  :)
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #28 on: February 05, 2018, 07:25:10 am »
You will need to have the auxiliary power supply working, otherwise the unit will appear dead. I think you should concentrate on here as the priority.
The big cap looks like it bulk on the top [maybe camera effect]. I suggest you take it out and measure the ESR. Don't measure in circuit. I would say never for suspected cap.
Oops, sorry, I thought someone might assume that when I posted that. I should have pointed out that that was an effect in the photograph. Please see the attachment.

If you suspect the transformer, then take it out of the board to inspect it closer and measure its primary and secondary inductance as well as continuity test. I have never seen transformer wire "burn" like this.  :)
Sorry, it is not "burnt", the look of the photo was due to the circumstances of taking the photo. The previous photograph was backlit using a light bulb behind the circuit board because it was so hard to get a photo of the wire.  |O (I might need a camera lens for photographing very small objects if I keep posting here.) The attached photo in this post is the very best one I could get after quite a lot of fiddling.  |O The broken wire is the one on the right. The fact that there is no continuity from that giant track into the transformer to anywhere else in the circuit board (see the pink circle in the previous photograph) seems very suspicious too.
 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #29 on: February 05, 2018, 07:45:25 am »
Can't tell from the picture if it's visually broken.
You sure you didn't measure on the enamel of the magnet wire, yeah? :)
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #30 on: February 05, 2018, 08:38:28 am »
Can't tell from the picture if it's visually broken.
No, you are exactly right, you can't tell from that photograph. That's why I shone a light bulb through the circuit board for this photograph:

https://www.eevblog.com/forum/repair/takasago-kx-210-power-supply/?action=dlattach;attach=392503;image

The point is, I don't have a camera which is good enough to take a photograph showing what I can see with my eyes, which is that the enamel wire is broken.

You sure you didn't measure on the enamel of the magnet wire, yeah? :)
Yes, I am very sure, because I was able to measure continuity from the transformer lead which I indicated with the pink circle on the back side of the board to the plus lead of the large capacitor, but not to any other leads on the transformer or any other parts of the circuit board except for that large power track which goes from the plus lead of the capacitor towards the transformer. That was the measurement which I thought was very odd, which is why I had a very good look at the transformer and found this. As for measuring on the enamel wire itself, I'd like to see someone try it.

Next stop is to desolder the transformer, and try to fix that tiny little wire.



 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #31 on: February 05, 2018, 08:49:47 am »
You know, for example switching transformer EMI screen is a screen [copper plate or wire] with 1 lead, normally connected to ground and nothing else.
But you can take it out and investigate.

Just don't investigate "too long" because these wires maybe fragile.  :)
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #32 on: February 05, 2018, 09:03:11 am »
You know, for example switching transformer EMI screen is a screen [copper plate or wire] with 1 lead, normally connected to ground and nothing else.
You are absolutely correct again. Please see the attached photographs.
But you can take it out and investigate.


Just don't investigate "too long" because these wires maybe fragile.  :)
You are always very helpful and concerned about everything, I feel glad to get your attention.
 

Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #33 on: February 06, 2018, 08:25:26 am »
I was able to remove the transformer from the board after quite a lot of effort with soldering wick. The through holes seem to be able to swallow a lot of solder and it was rather hard to get them out. I have attached two pictures of the broken wire. It is about 0.2 mm in diameter I think. At first I was planning to repair it using heat sink tube and 0.8mm diameter solid core wire from a doorbell, which you can see in the third photograph. That doorbell wire was just too thick to solder on. In the end I used 0.35 mm enamel wire which you can see in the fourth photograph. Wrapping the other end of the enamel wire around the transformer's leg was a rather delicate job but fortunately the wire and the solder joint survived that. I was able to resolder the transformer to the circuit board and I have confirmed continuity of the connections, as well as non-continuity of the things which aren't meant to be connected. The newly-soldered wire has a resistance of 9 ohms, which seems like a lot, but it is extremely thin wire. Unfortunately removing the solder with the wick left a lot of mess on the back side of the board, so I'm going to clean this up and then reassemble the power supply tomorrow. I don't have anything suitable for cleaning the board at the moment.



« Last Edit: February 06, 2018, 08:27:49 am by Asuka »
 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #34 on: February 06, 2018, 09:46:33 am »
 :-+ Well done, you found the fault.
With the transformer removed, can see the broken wire clearly.
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #35 on: February 06, 2018, 10:18:23 am »
:-+ Well done, you found the fault.
With the transformer removed, can see the broken wire clearly.
Thanks very much for your help.

If it starts working with this fixed transformer, I might write to the manufacturer and ask for a replacement for the transformer just to be on the safe side. I haven't replaced it back yet, since it's been a long day. I'll post an update when it's all back together.

 

Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #36 on: February 07, 2018, 01:29:55 am »
I put the power supply back together today and tried powering it up. Unfortunately the unit did not operate. I noticed the following symptoms: LD1, the pink circle on the left in this picture, lit up, and HS3, the heat sink behind the FET on the right, also circled in pink, got extremely hot, so that a smell was noticeable.

It's possible that the transformer failed again due to my repair breaking, or that I should have cleaned the back of the sub-board more carefully, or that I damaged something putting it all back together, or I failed to connect something properly, or there is another problem in the item somewhere.
 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #37 on: February 07, 2018, 07:28:41 am »
Did you manage to get a current draw this time? or the brightness of the lightbulb?

If its hot and smell, something is shorted. This is a easier repair than other types.
I would dismantle the connectors to all the outputs [power input is needed].
Check all the mosfets, diodes and caps.

The next time you want to run it, make sure the lightbulb in series method is used. When the light is bright, turn it off immediately.
« Last Edit: February 07, 2018, 12:10:33 pm by Armadillo »
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #38 on: February 10, 2018, 05:43:41 am »
Did you manage to get a current draw this time? or the brightness of the lightbulb?
I didn't have a light bulb in series, so I've spent some time rigging up an isolation transformer and current limiter.

If its hot and smell, something is shorted. This is a easier repair than other types.
I would dismantle the connectors to all the outputs [power input is needed].
Check all the mosfets, diodes and caps.
Yes, I will dismantle the unit, then clean it up, then check the continuity.
The next time you want to run it, make sure the lightbulb in series method is used. When the light is bright, turn it off immediately.
Got it. I have rigged up the light bulb as shown in the picture. Isolation transformer also made from back-to-back audio amplifier transformers.
 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #39 on: February 10, 2018, 06:48:24 am »
Ehmmmmmm....... You would need to know the KVA and the voltage drop. I don't know but I assume you did your maths.
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #40 on: February 10, 2018, 08:31:49 am »
Ehmmmmmm....... You would need to know the KVA and the voltage drop. I don't know but I assume you did your maths.
I did the maths of matching the transformers and checking the resistance of the coils, and I tested it out with a 12V AC power supply.

If I have a 100 W light bulb in series with the transformers, the most amperes that could possibly flow is 1 amp, and these are big audio amplifier transformers which take mains inputs. Both weigh about two kilograms with outputs around 50 volts, so I don't think there is any problem.  The output of the transformers is exactly the input voltage, 100V, if the bypass is switched on, and reduces to 95V when the light bulb is in series. I think it's adequate. I've also put a 3 amp fuse in between the transformers and the mains input.



 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #41 on: February 10, 2018, 10:18:46 am »
So, if its supplying 1A then theoretically zero volts is left for the DUT???
What is the Watts rating of the KX-210?

Edit: But if your objective is just to test for shorts and bypass thereafter, I suppose it should work for you.    :)
« Last Edit: February 10, 2018, 10:42:15 am by Armadillo »
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #42 on: February 10, 2018, 10:48:54 am »
So, if its supplying 1A then theoretically zero volts is left for the DUT???
I am surprised that the same person who suggested using this is asking this question. The bulb acts as a 100 ohm resistor in series, so the maximum current which may flow is 100V / (100 ohms + load), which is always less than one amp. It only goes to 1 amp through the light bulb if there is a short circuit.

My design is based on the one in this video:



What is the Watts rating of the KX-210?
Maximum input is 5.5A depending on the load.

http://www.takasago-ss.co.jp/english/products/power_electronics/dc/kx/kx.html

That would require a 600 W light bulb in series. I'm not planning to run this under load anyway.
 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #43 on: February 10, 2018, 10:59:37 am »
I am surprised that the same person who suggested using this is asking this question.

Don't be surprised. We are just trying to guide.   :)

The important thing is the Operating Voltage of the Takasago. What is the minimum voltage that it can operate so that you can check the circuit.
For example 0.5A X 100 ohms = 50V, so 50V remains for the Takasago. Will the transistor switch at 50V?
And how about at other starting or operating currents?
But always, never try never learn, aside from that the transformer will also drop some voltage other than the bulb.
I am not good at 100V supply.  ;)

Edit: You can always parallel another 100W incandescent bulb if not enough.  :)
But i am not sure of your audio power transformer back to back configuration especially effect on voltage drop.
« Last Edit: February 10, 2018, 11:11:22 am by Armadillo »
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #44 on: February 13, 2018, 07:04:45 am »
But i am not sure of your audio power transformer back to back configuration especially effect on voltage drop.
The output voltage is 100 volts, identical to input voltage. I have measured it with a multimeter. Anyway, I ran it for a half an hour with a 100 W light bulb and the correct-way-round transformer didn't even get warm. The wrong-way-round transformer got a little bit warm after half an hour. I don't think it's going to be any kind of problem.

Today I had some time and took the thing apart again. I cleaned up the mess I made last time, and started measuring continuity. There is continuity right across the gate and source of the mosfet which was getting so hot before. The part number of this MOSFET is 2SK1808, which seems to be this:

https://www.renesas.com/en-eu/products/power-mosfets/mosfets-for-switching/device/2SK1808.html

(link to English-language page). The gate of the mosfet is only connected with a 200k-ohm and 22kohm smd resistor,


so I don't see how it can be short-circuiting like that. Perhaps I misunderstood something. According to the data sheet there is a function like two zener diodes between gate and source, but I just get continuity with a voltage difference of less than one volt. I also measured the resistance, which was much less than one ohm. The package doesn't seem to be physically damaged at all.


 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #45 on: February 13, 2018, 08:35:18 am »
You are right to use ohms to measure shorts. if it is less than one ohm both ways [red and black probes reverse] it is then a definite shorts.
This warrant you to take out [desolder] the mosfet and confirm it externally that it is dead sure shorts before you order things around.
If you are able to take out the transformer, I am sure you can take out the mosfet. Just remember to retain any mica insulating sheet or the plastic screw sleeve.

Is this mosfet part of the auxiliary power supply? Seems rather huge?   ;D
 
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Offline Asuka

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Re: Takasago KX-210 power supply
« Reply #46 on: February 13, 2018, 11:13:04 am »
You are right to use ohms to measure shorts. if it is less than one ohm both ways [red and black probes reverse] it is then a definite shorts.
It's about 0.5 ohms on this multimeter, but it's not an EEVBlog multimeter but just RadioShack.
This warrant you to take out [desolder] the mosfet and confirm it externally that it is dead sure shorts before you order things around.
If you are able to take out the transformer, I am sure you can take out the mosfet. Just remember to retain any mica insulating sheet or the plastic screw sleeve.
Hopefully the mosfet will be easier than the transformer.

Is this mosfet part of the auxiliary power supply? Seems rather huge?   ;D
It's the same one as in the picture before, where I circled the heatsink in pink.

If the mosfet is faulty, it seems like I need to find a new replacement since this is no longer in production.

Putting V_DSS, V_GSS, I_D into Mouser I find STF4N90K5 from STMicroelectronics and FQPF4N90C from ON Semiconductor, and a few similar things at DigiKey. Is that a good way to choose a replacement, I wonder?
 

Offline Armadillo

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Re: Takasago KX-210 power supply
« Reply #47 on: February 13, 2018, 12:17:57 pm »
I would agree with the STF4N90K5 in TO-220FP package.

I suggest you remove the mosfet and measure again to confirm no other shorts.
From any DC capacitor after the rectifier, you measure ohms to make sure that the capacitor charges up to high enough ohms and not shorted or low ohms. If there are still shorts, the DC capacitors will show a short, meaning cannot turn power on. But still cursory measure each mosfet to be double sure, no more shorts.

Have you already study the auxiliary power supply at least it can output the voltage at the DC capacitor after the regulator or rectifier of the auxiliary supply?
You can isolate the main switching side by taking out some fuse or connector. Just test the auxiliary power supply for function.
Now you have the isolation transformer ready, you can use it to test it.
Be safe and take your time.
I always will forget to unplug and discharge capacitor after test. I think I need to tie a red string on my thumb for reminder.    :)
Wear a rubber glove and a safety goggle to add confident level.  :D
 
 


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