trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

voltage from 1 to 5 ?

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Hi I have done another series of tests. I haven't measured 1 to 5 voltage.

Yesterday started measuring the mosfet voltages with power on. I am not sure what Gate source and drain are but it seems the gate is connected to the gate of U1.

I have included illustrations of the wires of the mosfet that I measured anyway.

Imagine looking from above the mosfet and the flat side is facing towards the floor.

Results

Illustration 1. Measuring from the rightmost wire to the middle wire

Voltage = 320 V DC.

Illustration 2. Measuring from the leftmost wire to the rightmost wire

Voltage = -1mV DC to 0.9 mV DC (changing rapidly)
Voltage = 0.075 V AC
= 75 mV AC.

Illustration 3. Measuring from the leftmost wire to the middle wire

Voltage = 335 V DC.

Illustration 4. The test on the primary winding of the transformer

Voltage = 0 V DC.
Voltage = 0 V AC.

Bridging R2 (SMD resistor)

I measured R2 (marking 201 = 200 ohms) and it measured no continuity. So I bridged it with a 200 ohm through hole resistor. Then it measured 100 ohms and continuity. They were now working in parallel.
Testing the primary winding after bridging R2 showed 0 V.

When I disconnected one wire of the bridging resistor, again R2 measured no continuity and no resistance except through other paths (F1).

I'm not sure what to make of that. I don't know whether R2 is broken. I though it should show continuity.

R2 is connected to F1. It's possible that when F1 blew other components nearby were also damaged.

There is a SMD capacitor nearby and I think it's in parallel with a SMD resistor. I was wondering if I bridge it would it damage the circuit and would the primary winding register a voltage. But it's possible the capacitor is only smoothing and is not an obstruction to power to the transformer.

That's all. I am having trouble figuring out which is the Gate, Drain and the Source and made a thread about that, and someone said I might be reading it wrong because there is a diode there, but I didn't really understand.

Any advice is appreciated.

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

you need to understand your multimeter ..read about continuity testing and the ohms threshold for to get it to beep or whatever it does .think mine is about 30 ohms .. forget continuity test unless looking for short circuits .

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

There is an SMD 200 R resistor in circuit and I tested a 200R through hole resistor out of circuit.
The 200R through hole resistor tests continuity out of circuit.

The SMD did not register continuity until I soldered the 200R through hole resistor in parallel.
But you think it's not faulty and that at the size it won't measure resistance until it's larger than 200 R.

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

There is an SMD 200 R resistor in circuit and I tested a 200R through hole resistor out of circuit.
The 200R through hole resistor tests continuity out of circuit.

The SMD did not register continuity until I soldered the 200R through hole resistor in parallel.
But you think it's not faulty and that at the size it won't measure resistance until it's larger than 200 R.

no ..
what i think is your meter did not connect to it first time .

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

no ..
what i think is your meter did not connect to it first time .

I scratched both sides of the solder on R2 with a needle after it did not read anything. The reading I gave on this forum is after scratching the solder. No continuity on R2 and not reading a resistance. Only resistance was F1 ~12 ohms nearby.
After disconnecting one wire of the Bridging 200 ohm resistor, there was new solder left on R2 contacts and again it read no continuity and I read ~12 ohms from F1 and not the 200 ohms I was looking for.

Though I have not read wire 1 (ground) to pin 5 V_DD, I did read that there was power going through wire 1 to 5. I read across R1 (which is connected to wire 5) to wire 1. I did this because I didn't want to risk shorting those two wires. R1 is marking 245 = 2,400,000 = 2.4 mega ohms. The reading was

335 V DC, 0V AC.

But I don't know what the power directly across 1 to 5 is.

Edit: I just took a measurement directly from wire 1 to wire 5

Result Power On Reading U1 wire 1 to wire 5

1.285 V DC,
0 V AC.

That's without bridging R2 with a 200 R resistor.

Then I bridged R2 again with the 200 R resistor.

Wire 1 to wire 5 reads almost exactly the same

1.287 V DC.

So, is 1.3 Volts enough power?

Any advice is appreciated.

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

earlier post suggested 15v for the ic to work

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Thanks.

So are you sure now, that U1 doesn't work?
What are the pulses from the gate and the mosfet?
What are the power readings on the mosfet Q1 if that's not what should be powering the primary coil?



Also,


I have just put together a current limiter using a 60 W filament bulb, as one reply suggested and I was planning to do it.

When I plug in this power adaptor the light bulb doesn't go on. I didn't test if the adaptor had power, but I think it did, due to the next tests.
The adaptor has no load and is not connected to an output.

When i plug a usb Led lamp into the current limiter, the LED lights up, but the 60 W bulb does not light up.

When I plug a heater into the current limiter,
and switch the heater on, the bulb lights up,
but the heater does not heat up.

If I connect the heater to a normal socket it heats up.

The current limiter bulb is wired in series with the live (positive) wire.

Is my current limiter working properly?
Should the bulb be connected in parallel to the live and neutral?

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

bulb appears to work as expected . more current draw the brighter the lamp

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

Igoing through wire 1 to 5. I read across R1 (which is connected to wire 5) to wire 1. I did this because I didn't want to risk shorting those two wires. R1 is marking 245 = 2,400,000 = 2.4 mega ohms. .

and the million dollar question is what is R1 supposed to read ?

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

How do you know U1 wire 1 to 5 is supposed to read 15 Volts? Is that from the block diagram on the data sheet (that says 9.5v/15.5v VDD?
https://datasheetspdf.com/pdf-file/1...irst/SF5920S/1


I was wondering if this circuit has a separate standby/start up circuit and is it possible the voltages are from this?
Could the start up section be broken?
Is that part of the circuit inside the IC?

Also, I could take a reading directly across R1.

How do I find out what the voltage across R1 is supposed to be if the circuit was working properly?

Also, I was thinking of bridging some of the SMD capacitors (by placing a ceramic capacitor in parallel across it) to make sure they aren't broken and testing for output power.

I have circled them on the board in the photograph.
What value capacitors should I use. I have a range of ceramic capacitors.

The grey one at the top. Not sure that's a capacitor or fuse.

What is the part the I enclosed in a rectangle doing?
What does the part in the triangle do?

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

i meant R1 ohms not volts
never mind i see it now 2.4M

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

How do I find out what the voltage across R1 is supposed to be if the circuit was working properly?

voltage across it should be approx 320v if the highest voltage end of it is 335v.

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

I have reversed engineered some of the stages and marked them in the photograph (Reverse Engineering.jpg).

Primary Coil Voltage Tests After Re-bridging R2 and Bridging SMD Cap near primary coil
(See Photo: Test Setup.JPG)

I rebridged R2 (yellow circle), and bridged the SMD capacitor with a ceramic through hole capacitor marked (10 000 pF) (yellow circle). I measured voltage on the primary coil (red circles).

Result

Voltage = 0 V DC.
Voltage = 0 V AC.

Conclusion

The bridged components R2 and SMD capacitor near primary coil aren't the problem. Or they aren't the whole problem.


Reclassifying Previous Power Switching Mosfet Voltage Readings to Gate, Drain, & Source Voltages (Assuming the data sheet is right)

Power on

Gate to Drain
Voltage = 320 V DC.
Voltage = 0 V AC.

Gate to Source

Voltage = -1 mV DC to 0.9 mV DC (changing quickly)
Voltage = 75 mV AC.

Source to Drain

Voltage = 335 V DC.
Voltage = 0 V AC.

and in this previous test there was no voltage measured on the primary coil.


Recap of some previous important readings

Across R1 (which is connected to wire 5 (VDD) to wire 1 (ground) of U1.( R1 is marking 2.4 mega ohms)

The reading was

335 V DC, 0V AC.


More U1 Pulse Width Modulator IC Readings


Result Power On Reading U1 wire 1 to wire 5

Voltage ~1.29 V DC, (data reads it should be 9.5 V to 15V)
Voltage = 0 V AC.

(with and without bridging R2)

Test 2 wire 1 to wire 2. That is U1 ground to U1 gate.

Voltage = 0.4V DC to -0.1V DC, (changing quickly from one value to another).
AC = -0.4V (ripple?)

Test 3 PWM power U1 Ground to the far side of R1 (which is and SMD marked 245 (24,000,00 = 2.4MR).
335 V DC, 0V AC.

Test 1 mains power (Before F1 to the near side of D4 (relevant to pictures)
134 V DC, 114 V AC.


I think next

1. I will reverse engineer the circuit and use that to make sure that the conclusion that U1 is broken.

2. Perhaps take out Q1 mosfet and test it make sure what is the GDS and check if it registers faulty (though my component tester is the cheap £10 one and doesn't always work, finds good things bad).

3. After finalising conclusions, either leave the adaptor in a box, or salvage the components, since U1 is ~ £25 to buy and Q1 would need a substitute. I only wanted to learn from it, and it's not worth £25 to prove a point when I can buy a new adaptor for £5 and I won't be using this one even if it's fixed. Not sure though.

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

easiest thing to do here is measure ohms 1 to 5 on ic then fire hot air at the ic and remove it then check ohms again and also same places on the pcb where chip is missing .
and why you insist on bridging things eludes me .

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

easiest thing to do here is measure ohms 1 to 5 on ic then fire hot air at the ic and remove it then check ohms again and also same places on the pcb where chip is missing .
and why you insist on bridging things eludes me .

I don't have much experience, so I don't know what exact values I should be seeing. If the voltage is coming through a resistor or a SMD capacitor at either end of wires 1 and 2 of U1 or is part of the U1, Q1 stage or primary coil stage, and I bridge it, then I know that isn't what caused U1 or Q1 to read low voltage or incorrect voltages or pulses. It would be wrong of me to assume the IC or mosfet is broken if one of the connecting resistors is short circuit or open circuit.

What ohms?
Also you said U1 should have 15V across wire 1 and 5. Now you don't seem so sure.

Also, correction to the reverse engineering jpeg. Feedback (FB) is not disconnected. I'm not removing anything that is likely to break or break a trace until I have take lots more voltage readings.

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

there is a short circuit . its the capacitor or diode or ic chip .or R1 is open circuit

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

there is a short circuit . its the capacitor or diode or ic chip .or R1 is open circuit

Thanks.
How did you come to the conclusion that there is a short circuit in the capacitor, diode, IC or that R1 is open circuit?

Also If i remember correctly R1 reads 2.4 mega ohms.

[petehall347]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

because of the voltage right across R1

[Tarot Superstars]

Re: trying to fix a 6V 0.5A T1 (Transformer) AD050120T2 power supply

I previously measured voltages across source and drain of the mosfet Q1 with power on. But this doesn't tell me if there is any real connection between those two wires (which there should be) because I have really just bridged those two points and the voltage could be going to those two wires but not through Q1.

I am going this route because I am wondering why I have voltage across Q1 but nothing on the primary coil. There must be some open circuit or it's not switching on or something. So, I am trying to trace the voltage to the coil. I haven't finished reverse engineering the circuit yet so I haven't got far.

Is there any way I can check that there really is a voltage between source and drain, in circuit, with power on?

I have purchased a Vellerman HSP5 handheld oscilloscope, and it has a bandwidth of 1MHz and max voltage of ~ 600V, so that I don't have problems with grounding my CRT analogue oscilloscope.
Maybe this can be used to do some more checks, when I receive it.