BN44-00424A Continuous Restart

[senz_90]

Re: BN44-00424A Continuous Restart

Problem is I can't tell a secondary output diode from a feedback diode so if somebody wants to point them out I will gladly try that.

did you have the service manual or psu schematic? from i know feedback lines usually connected to optocoupler or some ic that has this pins for feedback. smps is mysterious and various, when you learn much you will know that is not enough but you've got fun!! and this is the reasons to makes me learn it deeper.

[mmartell]

Re: BN44-00424A Continuous Restart

Cannot find a service manual or a schematic for the ps.

Speaking of octocouplers I have a pair of them on this board. How do you test them and if they fail to provide feedback won't that shut down the ps ?

[selldoor]

Re: BN44-00424A Continuous Restart

You can test one side easy as its just a diode - other side is more difficult
http://www.antimath.info/electro/how...n-optocoupler/

[mmartell]

Re: BN44-00424A Continuous Restart

Excellent!

[mmartell]

Re: BN44-00424A Continuous Restart

So I have three octocouplers on this board. The first two test like diodes with a forward voltage drop just over a volt and no voltage in the opposite direction.

The third has a forward voltage drop of .74v in one direction and .85v in the other. Thoughts ?

[senz_90]

Re: BN44-00424A Continuous Restart

I am still prefer test diode, transistor, or this optocoupler with analog vom. it easier when test the emitter collector legs with analog one. but the others used to using digital meter and would help you. btw you have 3 optocoupler is I don't look wrong way.

[LDSisHere]

Re: BN44-00424A Continuous Restart

So I have three octocouplers on this board. The first two test like diodes with a forward voltage drop just over a volt and no voltage in the opposite direction.

The third has a forward voltage drop of .74v in one direction and .85v in the other. Thoughts ?

Are you testing it out of circuit? If yes, then it is bad. If no, it could e because of something else in the circuit. There is often resistors across those legs.

[mmartell]

Re: BN44-00424A Continuous Restart

I tore apart the panel after reading some other threads and found one of the led backlight strips had many dead led's, two of which failed open.

I put a jumper across both and reinstalled the strip and the power supply. It fired right up and never shut off. Turns out the PS is intolerant of no load condition on the led driver circuit.

Thanks for everyones input but power supply malfunction in this case turned out to be a red herring as the malfunction was "expected behaviour".

THREAD CLOSED

[senz_90]

Re: BN44-00424A Continuous Restart

lol. this proof sam's page at repairfaq site, don't always think your problem is complicated.

[budm]

Re: BN44-00424A Continuous Restart

The LED drivers have detection circuit to detect shorts or open LEDs circuit. Glad you finally found the real cause of the problem.

[senz_90]

Re: BN44-00424A Continuous Restart

The LED drivers have detection circuit to detect shorts or open LEDs circuit. Glad you finally found the real cause of the problem.

is this means there is feedback circuit likes lcd tv inverter circuitry?

[Ltank]

Re: BN44-00424A Continuous Restart

Next time ,When you have the power supply removed look on the back foil side at ZD585 to connector that goes to the main board there is a code on the three legged SMD. I cant read mine. What is the code? I have a service manual but no shematic or parts list for parts on the board were provided.
Thanks
Ltank

[budm]

Re: BN44-00424A Continuous Restart

From the way that Zener is hooked up, it looks like one of those XX431 Vref DIODE:
http://www.mouser.com/ProductDetail/...4AAymvcTt%2fGG

https://cdn.badcaps-static.com/pdfs/...f3f88c819d.pdf
see fig 8

[jeremyz2006]

Re: BN44-00424A Continuous Restart

Hello,

Sorry to post onto your thread but due to the new user rules I cannot open an new thread I am looking for the schematic drawing to BN44-00424A I cannot seem to find in anywhere if someone could attach it that would be great.

Thank you