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Products => Test Equipment => Topic started by: marketta49 on November 09, 2017, 10:36:25 pm

Title: Problem power supply Tech Star K3010D
Post by: marketta49 on November 09, 2017, 10:36:25 pm
Hello everyone
I take advantage of my new subscription to your site to inform you that I have a problem with my 10Ampere Tech Star K3010D power supplying a LW-K305D-1 motherboard that is similar to the 5 Amp power supply K305D.
The problem with my Tech Star K3010D is that it stays fixed at 32Volt maximum and turning the non-adjusting pot always stays at 32Volt.
I ask you open that you are expert what can it be?
The components (ICs) are:
LM324 8Pin
LM2904 8PIN
Thanks to who solves the problem
Title: Re: Problem power supply Tech Star K3010D
Post by: marketta49 on November 10, 2017, 02:04:36 pm
I attach mother board photos
Title: Re: Problem power supply Tech Star K3010D
Post by: cat87 on November 10, 2017, 02:27:38 pm
and turning the non-adjusting pot always stays at 32Volt.

Well, there's your first clue. Maybe you should try turning another pot that actually does something  :-DD

Sorry for the bad joke, I couldn't help myself.

Now, here's some actual advice:

Thanks to who solves the problem
Sorry, but it doesn't work like that. Some people may come up with possible failure modes, then it's up to you to actually check if that is indeed the cause.

The "pot"... is it  an actual potentiometer or an encoder?
First thing, maybe the pot itself is dead. Try checking it to see, maybe the wiper got stuck on full tilt. Or if it's an encoder type. maybe something happened to the digital section reading it.

Because the unit is stuck on the maximum voltage, the first IC i'd suspect  is the SG3525. Either the feedback (resistor divider on the output maybe?) path is damaged  or the IC itself is bad.
Get the schematic for it and a scope and start checking it had the right signals on the pins.

Hope this help, but with the limited info you gave, that's about all I can come up with. A schematic attached to you post  might help :D
Title: Re: Problem power supply Tech Star K3010D
Post by: marketta49 on November 12, 2017, 03:01:54 pm
I thank you for the answer
you do not have to apologize, you have to always skimp, you're good at joking over it.
Then returning to repair and troubleshooting info you info that is a multi-turn potentiometer and I've got it and it's ok.
For the IC sg3525ap Pulse Width Modulator was my first thought and I replaced it but did not fix it.
Now my suspicion is that a port of the quad operating LM324 is broken
then I will try to verify.
I send the electrical diagram attached.
then let me know by looking at the scheme
Title: Re: Problem power supply Tech Star K3010D
Post by: marketta49 on November 12, 2017, 03:05:12 pm
I have attached the schema of k305d by 5Ampere, because it is the same as the schema change only the power FETs for the rest is the same
Title: Re: Problem power supply Tech Star K3010D
Post by: Chris56000 on November 12, 2017, 06:24:30 pm

This is a "primary-side" regulated power-supply that contains THREE distinct power-supply sections:-

1) A low-power section consisting of U5 (TNY280) and T1 which provides +/-12 V for the front panel voltmeter/ammeter PCB on the front-panel;

2) A second (momentary self-oscillating) "housekeeping" supply - this consists of T2, Q17, Q18 and Q21 and provides by bridge-rectification, the startup and control supply for the main PWM controiler U4, (SG3525) for the first few cycles of oscillation, until PWM drive is produced from pins 11/13 of U4 to maintain the control supply. Transformer T2 is both a self-oscillating housekeeping transformer during the initial start-up phase, and then the main drive transformer for the half-bridge output stage once enough volts has built up across C20/C21 for U4 to become operational;

3) The main variable high-current supply, consisting of U4, half-bridge transistors Q21 & Q22, main controlled transformer B1 and current-sensing transformer B2. The primary return for B1 is the centre-point of the two main HT smoothing electrolytics C23 & C44.

A) Begin by checking the power-supply voltage for the SG3525 U4 across pins 3, (-ve) and 13, 15 (+ve), about 12V DC should be present across these points - if low, make sure C20 & C21 aren't low in value or o/c., whilst if missing test Q17, Q18, D19, also Q19, Q20 and D15, and the soldering to the pins of the housekeeping supply/driver transformer T2.

B) If a satisfactory supply-voltage is present across pins 3 & 15 of U4, transfer your meter-probe red lead to pin 5 of U1 - the voltage here should vary 0 to +5V with adjustment of the front-panel voltage control. If the voltage on the terminals of the Voltage Control is missing, this points to a wiring-fault, an internal failure of U4 or a possible fault in U1 or U2 - pin 16 of U4 is a 5V Reference O/P used by the voltage & current controls, derived from internal circuitry within the PWM controller U4.

C) Next, if you measure a good variation at pin 5 U1 with the front panel control, transfer the red meter lead to pin 1 of U4 - absence of control indicates a fault in U1, Q8, Q9 or Q10, best tested by substitution. Preset controls W2 and W3 adjust the max/min output voltage limits. Feedback to close the control-loop is from the positive O/P terminal via resistors R48, R49 & R50 in series, whilst a.c. feedback to help cancel noise and O/P ripple is via C30 and R44, the high-value electrolytic C29 purely a d.c. blocker.

D) Make sure approximately 7.5V is present across D4, if you need to replace it, use 1 x BZX61C7v5, and make sure C13 is OK as the SG3525 may oscillate if C13 is low in value or O/C, this is an internal reference for the internal error-amplifier in U4.

You should be able to get 2SC1815 & 2SA1015 cheaply in packs of 10 on fleabay, alternatively I've found BC182L (NPN) and BC212L (PNP) are drop-in substitutes but PLEASE make sure you get the "L" type!

Let us know how far you get with all the tests I've given here, and I'll post some more if you're still stuck!


In all the above I've assumed the voltage/current displays on the front panel are lit, proving the +/-12V supply from T1 present and correct, or reasonably so!

The circuit drawing for the front-panel PCB presumably was drawn/designed on the basis of being fed from a centre-tapped 50Hz
mains-transformer winding, but the circuit works just the same using the rectified DC supplies from T1!

Chris Williams
Title: Re: Problem power supply Tech Star K3010D
Post by: marketta49 on November 12, 2017, 09:48:10 pm
hello Chris for the beautiful answer to the evidence I have to do.
I did the tests you told me and I recounted how much he said:
1) Volt on 5 / U1 LM324 FIXED a 5Volt
2) Was up to 13-15 / U4 sg3525 OK 12volt
3) Was su 16 / U4 OK 5 Volt
4) Was on D4 OK 7.5Volt
5) I found the value of W1 different from the schema ie was mounted a 5K trimmer instead of schema is 1K before replacing it, can trimer be the cause of the defect?
I await your response
Title: Re: Problem power supply Tech Star K3010D
Post by: marketta49 on November 13, 2017, 03:52:58 pm
Hi Chriss I think I've solved, list you what are the problems.
1) The Vout regulating potentiometer VR is broken
2) Two wires on the VR potentiometer were inverted to the right
3) the trimmer V1 as you can see in the diagram is from 1K but the scheme refers to a power supply of 5ampere K305D, but being the power supply in the K3010d by 10 amps I think the 5K trimmer is fine with a hike greater than current.
I thank you for having made me all the tests that have been very useful and you were right that you could be the broken VR or cabling error.

The potentiometer 1 and 2 wires were reversed and furthermore it was broken open 1 and 3
I attach photo
Title: Re: Problem power supply Tech Star K3010D
Post by: Chris56000 on November 13, 2017, 08:15:04 pm

Well done on getting your unit working!

The original schematic provided by the manufacturer is like a Chinese Cryptic Puzzle and not particularly easy to follow, but basically U1A/U1B and transistors Q8, Q9 and Q10 control the voltage from the wiper of the voltage panel control and invert it so when the voltage–control is at maximum, the feedback from R48, R49 & R50 is a minimum and the PWM controller U4 produces maximum duty–cycle output for the main power stages, and therefore transformer B1 gives maximum voltage output.

As the voltage control is rotated anticlockwise, the feedback from the output via R48, R49 and R50 is allowed to increase by the action of the control circuit U1, etc.,  and the effect on U4 causes the duty–cycle of the PWM switching waveform fed to B1 primary to reduce, therefore the output from B1 secondary reduces to correspond to the reduction in voltage from the front–panel voltage control.

This design means there is no high–power bipolar or MOSFET devices are needed in the positive output lead and the cost, weight and heat produced by series regulation devices is avoided!

Chris Williams
Title: Re: Problem power supply Tech Star K3010D
Post by: marketta49 on November 20, 2017, 08:56:05 am
Chris thank you for the technical information
however I managed to solve with the experience of Chinese products.
They are working but require deep control over cold welding and wiring, the Chinese produce a great deal of quantity and do not do the tests, they just have to sell.
Anyway thanks
Title: Re: Problem power supply Tech Star K3010D
Post by: Chris56000 on November 20, 2017, 09:19:25 pm

My pleasure Mario!

In many cases there's nothing intrinsically wrong with the design of many pieces of Chinese Electronic Test Equipment, what lets it down in so many cases is:–

1) Very poor or non–exsisting documentation,  manuals written in "Chinglish" and circuits drawn like Cryptic Chinese Puzzles – assuming you can get one at all that is;

2) Cheap components and plastic finishes, etc;

3) Variable quality control and safety – you really DO have to inspect every unit you purchase!

4) Unreliable/self-destructing firmware and no means of re-flash (Feel-Tech & Co., Are you reading this?!)

Hope your PSU gives you many years of reliable service now!

Chris Williams
Title: Re: Problem power supply Tech Star K3010D
Post by: bruno rafael on July 25, 2020, 06:16:16 pm
hello all, i have problem in my powersupply, i read all post in this topic,and i have one problem...

my powersupply is identical  ( LW 30v10A) but dont have w1 and D4 in my motherboard.........please help-me!
Title: Re: Problem power supply Tech Star K3010D
Post by: mava70 on January 30, 2021, 08:37:40 pm
Hi everybody,

I did a modification to he mosfets putting a resitor in series of the source for driving more hard the two main fet as suggested on a youtube videos, but I did a mistake I put a 22k resistor on one of the two indeed of 22 ohm :(. During testing at 12V no problems seems occurring, but turning voltage up I got a short and the main house switch cut off. After finding the error I dismounted the fet with the 22k resistor in series (the bottom one) and found it is shorted out on all 3 pins. The strange thing is that the main fuse is intact, also the added 22k resistor on the source is intact. I ordered a brunch of FET for substitute it, but I suspect more faults can be generated by the short.

Someone has some suggestion on how to troubleshoot this?  Can I power on the main low power circuits by another power supply and measure all things around the two fets without feeding in a 220V that can lead in other major faults?

Any suggestion on how to do it?

Thanks everybody.
Title: Re: Problem power supply Tech Star K3010D
Post by: dompower on August 31, 2021, 06:06:19 pm
I appreciate Chris56000's analysis.
He is right.
I had one LONGWEI LW-3010D.
I did not get any output volt, the LED showed 0000 volt.
C16 1000Mfd was completly short. After replacing the capacitor still did not work.
I found out T1 output after D5 was just 6.9v.
I struggled a lot to fix but no use.
Finally I connected an external 12v/1A SMPS to D5 cathod, everything worked fine.
The powersupply is working fine. Why the T1 12v output is reduced,
may be since the C16, smoothing capactor shorted, it might have affected the secondary of T1.