Benq 24" Led need help! PSU problem

[Jester2000]

Hi, all and thanks for reading.

I have acquired a 24" LED Monitor BENQ G2420HDBL that is totally dead. When stripped down I noticed an IC with half the top missing on the PCB. Looks like a switcher for low standby - power off? Trouble is, how can I identify it or can anybody suggest an alternative? It doesn't look blown (no charred or burnt parts and doesn't smell like its burnt out) guessing it just been miss handled.

PSU Part number is E162032 VOL.3 ?

Pin 1 Primary side of transformer
Pin 2 to Opto coupler?
Pin 3 n/c
Pin 4 Primary side of transformer

Pin 5 to Pin 8 Ground

I bow down to your superior knowledge! Please help!

Barry

[PlainBill]

Re: Benq 24" Led need help! PSU problem

I've got some clues; it's going to require more research. The chip is by Power Integrations. TOP2xx appears to be their designation for a line of SMPS controllers. At the moment all I can do is eliminate the TOP232 - TOP234 and TOP242 - TOP250 devices.

While it is possible I could identify it myself, I don't want to deny you the opportunity to do it yourself. The Power Integrations, Inc website is here.

PlainBill

[Jester2000]

Re: Benq 24" Led need help! PSU problem

Thanks for the reply, Looking at the digikey website, I've got a choice.

The only difference appears to be frequency range and wattage.

I suppose the highest wattage will cover it? Its an LED display so I don't have to worry about CCFL drivers.

Which is the best one to go for? Or will they all do the same job?

Thanks again

Barry

[PlainBill]

Re: Benq 24" Led need help! PSU problem

Thanks for the reply, Looking at the digikey website, I've got a choice.

The only difference appears to be frequency range and wattage.

I suppose the highest wattage will cover it? Its an LED display so I don't have to worry about CCFL drivers.

Which is the best one to go for? Or will they all do the same job?

Thanks again

Barry

Suggestion: The easy approach would be to look at the back panel of the monitor. It should show a wattage. Choose one rated for a higher wattage.

A more liberal approach would be to examine the datasheets for typical applications and see if that gives a clue. It appears Power Integrations has a number of design examples on their site. I'd expect that one is a match.

Do check all associated components. To me the damage looks like the chip shorted and exploded.

PlainBill

[Jester2000]

Re: Benq 24" Led need help! PSU problem

Suggestion: The easy approach would be to look at the back panel of the monitor. It should show a wattage. Choose one rated for a higher wattage.

A more liberal approach would be to examine the datasheets for typical applications and see if that gives a clue. It appears Power Integrations has a number of design examples on their site. I'd expect that one is a match.

Do check all associated components. To me the damage looks like the chip shorted and exploded.

PlainBill

Thanks for all your help, plumped for 1.37 Amp output up to 38 watts. Normally i'd agree with the blown component theory but this was bought and it looks like it has never been used, it still has all of the protective plastic all over it! Also there is absolutely no burn or scorch marks anywhere on the board and there isn't that smell you normally get from blown components. Either way, for £1.60 I'll throw one at it and see what happens.


I'll let you know what happens!

Barry

[Longbow]

Re: Benq 24" Led need help! PSU problem

Great photos, thanks. That device is a new one on me. It is a combination switching FET and opto coupler. You can see they even notched out the pc board for greater isolation between primary and secondary. A shorted FET would blow the part up like that. The next step is to check parts in the vicinity - especially any low value resistors.

[PlainBill]

Re: Benq 24" Led need help! PSU problem

Great photos, thanks. That device is a new one on me. It is a combination switching FET and opto coupler. You can see they even notched out the pc board for greater isolation between primary and secondary. A shorted FET would blow the part up like that. The next step is to check parts in the vicinity - especially any low value resistors.

When I was a little boy my Grandma reminded me of a saying sometimes attributed to Mark Twain, sometimes to Abraham Lincoln. "It is better to remain silent and be thought a fool than to open one's mouth and remove all doubt."

You are correct. The pictures are excellent. After that - well, I'll follow Thumper's Law. You can even see the optocoupler straddling the white line. It's IC602. IC601 is a SMPS controller and power FET in a single package. It's a member of Power Integrations, Inc TOP252 family.

PlainBill