Author Topic: Problem power supply Tech Star K3010D  (Read 3781 times)

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Offline marketta49

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Problem power supply Tech Star K3010D
« 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:
2X10N60C
1xMBR20200CTG
SG3525AP
LM324 8Pin
LM2904 8PIN
TNY280GN
Thanks to who solves the problem
 

Offline marketta49

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Re: Problem power supply Tech Star K3010D
« Reply #1 on: November 10, 2017, 02:04:36 pm »
I attach mother board photos
 

Offline cat87

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Re: Problem power supply Tech Star K3010D
« Reply #2 on: November 10, 2017, 02:27:38 pm »
Quote
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:

Quote
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

Offline marketta49

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Re: Problem power supply Tech Star K3010D
« Reply #3 on: November 12, 2017, 03:01:54 pm »
Hello
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
 

Offline marketta49

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Re: Problem power supply Tech Star K3010D
« Reply #4 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
 

Offline Chris56000

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Re: Problem power supply Tech Star K3010D
« Reply #5 on: November 12, 2017, 06:24:30 pm »
Hi!

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!

Note:-

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
« Last Edit: November 12, 2017, 09:34:07 pm by Chris56000 »
It's an enigma that's what it is!! This thing's not fixed because it doesn't want to be fixed!!
 

Offline marketta49

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Re: Problem power supply Tech Star K3010D
« Reply #6 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
Mario
« Last Edit: November 12, 2017, 09:50:19 pm by marketta49 »
 

Offline marketta49

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Re: Problem power supply Tech Star K3010D
« Reply #7 on: November 13, 2017, 03:52:58 pm »
SOLVED
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
« Last Edit: November 13, 2017, 04:01:27 pm by marketta49 »
 

Offline Chris56000

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Re: Problem power supply Tech Star K3010D
« Reply #8 on: November 13, 2017, 08:15:04 pm »
Hi!

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
« Last Edit: November 13, 2017, 08:22:14 pm by Chris56000 »
It's an enigma that's what it is!! This thing's not fixed because it doesn't want to be fixed!!
 

Offline marketta49

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Re: Problem power supply Tech Star K3010D
« Reply #9 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
Mario
 

Offline Chris56000

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Re: Problem power supply Tech Star K3010D
« Reply #10 on: November 20, 2017, 09:19:25 pm »
Hi!

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
« Last Edit: December 16, 2017, 07:15:32 pm by Chris56000 »
It's an enigma that's what it is!! This thing's not fixed because it doesn't want to be fixed!!
 


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