Intertek S003IV0600050

[semiRocket]

Hi,

I have a faulty 6V, 500mA switch mode power supply, I suspect the switching? IC is faulty since the switching transistor seems OK. The only issue is I can't find any information on this chip. The chip is in a SOT23-5 package with markings PB07. Any info appreciated.

[Andrew F. Ali]

Re: Intertek S003IV0600050

First I would try to remove that white glue from the top of the board. Pull each of those e-caps and check their ESR and cap value. Test all the diodes and resistors to verify if they are OK. On the underside I would check the value of the SMD resistors to verify they are good. Test the ceramic caps to verify they are not shot circuiting. Verify to see if the IC is getting VCC and measure the other pins to see what is being put out. Then depending on the cost buy a new PSU as they are very inexpensive.

[semiRocket]

Re: Intertek S003IV0600050

Thank you for your suggestions. I've checked the components on the hot side, I am not worried about output side for now since I am not getting any activity. On the hot side, diodes are OK, E-Caps capacity is OK, ESR is maybe a little bit on the high side, but I think it is OK for the mains frequency. Resistors values are OK. Ceramic caps are not shorted. Not sure what pin on the IC should be VCC, but I am not getting any voltage on any pin for that matter. There is no switching activity as far as I can tell. There is a steady 316V on the collector of the transistor (NPN) B-C-E.
Also clearing this silicon gunk is not possible without damaging components. But I don't think it is worth it anyway - I don't think there is something hiding there. Single sided board, with some SMD component from the bottom.

[R_J]

Re: Intertek S003IV0600050

Are you sure about the number? could it be PH01 which would be a TPS61040, have you checked the green resistor and the L2 coil

[semiRocket]

Re: Intertek S003IV0600050

Yes, I am pretty sure it is a PB07. I can see it rather well with the naked eye, sorry I about the camera quality. The green resistor is a coil, spot on 460uH as the colors says. The coil is on the negative rail of the two big capacitors that goes to the IC pin 4. Pin 5 of the ICis connected to base of the transistor. PIn 1 is connected to the positive of the capacitor C5, which does not have any voltage when the circuit is on.

The component marked as L2 is showing very low resistance, not sure about the inductance value yet.

[semiRocket]

Re: Intertek S003IV0600050

Also, pin 2 of the IC is connected to ground, and it is only about 7 ohms in regards to pin 1 with C6 and C5 out of the circuit, which doesn't look right to me. But maybe the low resistance is from the winding of the transformer.

The two 3 mega ohm in series are connected to the positive rail of the big capacitors and the pin 1 of the IC. Looks like a startup circuit.

[Andrew F. Ali]

Re: Intertek S003IV0600050

Then the only suspects for me would be the Switching Transistor and the PWM IC. The transformer hardly goes bad but it could. I wanted the glue removed not to look for hidden components but this glue tends to become conductive as it ages.

[semiRocket]

Re: Intertek S003IV0600050

OK, I tried to measure the silicon's gunk resistance by putting the highest range my multimeter can handle, and I could not register any. I suspect the IC as the transistor look OK as the low resistance of the IC pins 1 and 2 looks very suspicious to me and I can't find any path which would blame the winding. Winding (feedback?) is less then 1 ohm in resistance anyway. I suspect it is a dead end, but nevertheless, it was fun diagnosing

[Andrew F. Ali]

Re: Intertek S003IV0600050

Yes... I had some fun too...So final analysis....get a new one??

[semiRocket]

Re: Intertek S003IV0600050

Nope, I don't need it right now it can wait until more info.

The transistor is liberated it looks like it is 3DG3020. I found something unusual, though. I am getting around 0.77V drop from emitter to collector and not the other way around.

EDIT: Which might be explained by the diagram found here:

[Andrew F. Ali]

Re: Intertek S003IV0600050

On the Diode scale, with the RED lead on pin 1 (E) and the BLACK lead on pin 2 (C) you could get a reading as the in built diode (damper) would be fwd biased and in the reverse leads open, which may seem OK. Try putting the RED lead on pin 3 (B) and the BLACK lead on pin 1 and then on pin 2 and see if the readings are low and reverse the leads putting the BLACK lead on pin 3 (B) and the RED lead on pin 1 and then on pin 2 and see if the readings are high.

[semiRocket]

Re: Intertek S003IV0600050

Yes, the transistor is otherwise giving a typical readings of the NPN type in regards to voltage drop.

[Andrew F. Ali]

Re: Intertek S003IV0600050

So it could be good. That leaves the PWM IC. According to the cost I would have liked to buy them both, test them individually out of circuit to determine if diagnosis is correct, then install the new components. and if it works.....HAPPY...if not throw it through the window....