362142 pwm ic chip.............what it might be? Vd

[Francesc V.]

I am trying to fix this 24Vcc swich power supply that has no output voltage. The problem might be in the PWM controller, however, I haven't been able to find the datasheet for this PWM IC tiny controller. Any idea?

(I am attaching some pictures for a better understanding of my troubleshooting)


Tracking the PCB:

GND pin 1
Feedback pin 2
RI pin 3 (100k between pin and hot ground).
Sense pin 4 (470ohm to source)
Vdd is pin 5
Gate pin 6

Maybe it's just an OB2262/ OB2263MP (or could be replaced by these ones). Pinout seems the same.

When I am plugin it the PCB (as it's like in the picture), Vdd starts increasing and get's stable at about 79V!!!! Vdd cap hasn't exploded yet, but it's rated 50V. This seems so much for a PWM controller..............what's might wrong there?

Between R1 and R2 there are 3M ohm (in the middle point 1.5Mohm), then it goes R3 with 200k...........at this point there is Vdd entrance...........also connected to the cap, diode and then hot earth..........that high voltage on Vdd is because IC is not installed?
Also.......all this bunch of resistors are connected in the AC entrance............before the rectifier. Not as in the OB2262 schematics.

Lost in translation.......trying to understand :-)

Regards,
Francesc.

[Francesc V.]

that high voltage on Vdd is because IC is not installed?

Yes!! with the IC installed the voltage decreases between 13-16 V...................but fluctuates!!

Fluctuates with mosfet installed or without...........doesn't matter. Vdd cap is in good conditions (10uF 50V and low ESR).

What could be the reason of fluctuation? Faulty IC?

I will check in the meantime the optocoupler............not sure if it can be "shorted" to just check the primary side.

Regards,
Francesc.

[truclacicr]

The typical fault with these supplies is that the capacitor on Vdd dries out and goes high ESR.

When the IC is in start mode, the Vdd capacitor is charged from the main rectifier by the resistor, typically 100K or more. When the voltage reaches a certain threshold, the IC switches to run mode and pulses the MOSFET. The capacitor's charge is then replenished via the auxiliary secondary winding of the transformer. If the supply doesn't come up, such as when there is a shorted output, then the capacitor's charge is depleted until it falls below the start threshold. The IC then reverts to start mode and the cycle repeats. This results in hiccuping.

[CapLeaker]

It fluctuates on Vcc because it's trying to work, but can't. This does not automatically indicate the PWM is bad. As already mentioned in post #3 usually what goes bad is either the capacitor or the starter resistor is bad (higher ohms than it should be). I had a bad case of that starter resistor going bad. It measured good when cold, but after 20seconds the PWM stopped because the resistance was then too high not giving enough Vcc for the PWM.

[Francesc V.]

I will have a look to your comments.......thanks!. Let's see who gets the BINGO.

In this case, the output is flat always. No variation of any voltage at all. I am saying this because sometimes when something is shorted on the secondary, you see some fluctuation.........not sure if it's a fact or I am completely wrong.

Will check all SMD components starting in the primary section. As I said, Vdd cap is in excellent conditions so far. I will pay attention on the resistors.

Regards,
Francesc.

[lotas]

This is OB2362AMP

[harp]

ob2362a

[Francesc V.]

I''ve ordered the chip.........let's wait for the final outcome.

I haven't found any damage resistor (startup resistor is fine at 20k). Also Vcc capacitor looks good in capacitance and ESR. Furthermore I don't see any gate signal in the oscilloscope.

[CapLeaker]

Also could be that the chip is in a protection mode somehow.

[Sam Scarbo]

Sometime ago, i tried to troubleshoot a 12V wi-fi router adapter that has gone bad. After a few hours of experiments and some exciting firework/sparks, when I found the OB2263 family SMD chip (with "61050" marking on it) was dead, I gave up.

You said you have ordered your OB2362a chip. You should also check the MOSFET is not damaged.

Good luck!

[Francesc V.]

I''ve ordered the chip.........let's wait for the final outcome.

I haven't found any damage resistor (startup resistor is fine at 20k). Also Vcc capacitor looks good in capacitance and ESR. Furthermore I don't see any gate signal in the oscilloscope.

I give up on this one........xDD

Chip changed.......but same result. Vdd chip is fluctuating / restarting
Starting up resistors changed,
No voltage detected in pin 3
Voltage output sligthly increases within minutes from 0 to a 1.7V (nothing seems shorted on the secondary section).

I've changed TL431, checked resistors there.........and also the optocoupler.

Too much time invested on a shitty SMPS. xDDD