BN44-00264A buzzing

[petehall347]

Re: BN44-00264A buzzing

Change the pfc Ic whoch is a fan7529 I believe should sort the issue Ive done a few same issue. These sets power the inverter straight off the Pfc bus and the pfc Ic fails to turn on the pfc fets as much meaning the pfc caps voltage drops and becomes unstable causing noise on the inverter trannys.

i already changed that ic which is actually fan7530 ..are you saying use fan7529 instead ?
i have suspected this all along . i have 3 more so will try a different new one just in case i got a bad one
do you know the expected voltages at fan7530 ic ? i would rather diagnose this than risking board damage .i do have a scope but only 40mhz if i need to look at waveforms .i use it mainly for audio repair as that is what i do mainly . i am just learning about switching supplies .

[ReeceyBurger123]

Re: BN44-00264A buzzing

Sorry it is a 7530 ok, right what does the pfc measure then ? Also Ive not got much time so just skim reading threads atm sorry.

[petehall347]

Re: BN44-00264A buzzing

Sorry it is a 7530 ok, right what does the pfc measure then ? Also Ive not got much time so just skim reading threads atm sorry.

i have to take voltage readings as yet . i wanted to know what to expect and what frequency . i dont want to waste another 100 quid on a dmm in case it blows it up . had that happen 3 times with different things now . its cheaper using the scope if i can .
i will see if i can find a data sheet for the chip to see how it operates first . knowing how things work is half the battle . i was brought up with valves and can deal with them and transistors of the bjt sort . i am 56 and still learning . i hate to throw things away .

[jetadm123]

Re: BN44-00264A buzzing

As mentioned in earlier post: check the voltage across the main cap, it should read around 400Vdc. If you don't see it, then the PFC circuit is not working. Since the FAN7530 is the PFC controller, you must measure the Vcc (pin 4). Use pin 6 or the neg. lead of the main cap as your ground. Minimum startup voltage at pin 4 for the FAN7530 is 11Vdc. If you don't see this, then something is either wrong with the FAN7530 or a problem with a component connected to pin 4.

As mentioned in post #15, you seem to have problems with the diodes and resistors. If they are indeed shorted, then they will definitely cause problems as the diodes are connected to the output of the FAN7530. Suggest you remove them from the circuit for further testing.

[petehall347]

Re: BN44-00264A buzzing

voltage at main caps is 390v .
everything is working correctly on the set . as in picture audio and back lights .
its just this loud buzzing /switching noise .coming from the board around the pfc circuit
and the strange looking power draw at the mains plug . which actually drops and noise also lowers when i warm up the area around the pfc circuit . it is proving difficult to narrow down a specific component by warming it up as the cause as its a 2 sided board .

[ReeceyBurger123]

Re: BN44-00264A buzzing

Maybe get a can of freeze spray then and freeze parts to see if one part causes the buzzing ? Also there is a polly cap I belive that fails on this board as well will have a check later.

[petehall347]

Re: BN44-00264A buzzing

Maybe get a can of freeze spray then and freeze parts to see if one part causes the buzzing ? Also there is a polly cap I belive that fails on this board as well will have a check later.

i have tried the freeze spray but i am not seeming to be getting closer to it .
it does seem to be lp801s mainly buzzing but i am thinking something is making it buzz rather than loose lamination's because of the odd looking power draw from the mains supply

[petehall347]

Re: BN44-00264A buzzing

we have a winner reeceyburger123 was bang on the target ..... silence is golden ...
another new chip has it solved .
i did have fun before changing it though spent 3 hours swapping main filter caps and checking caps after pulling them out . plus i swapped the bridge rectifier too .

[CapLeaker]

Re: BN44-00264A buzzing

So you changed out the PWM again and that fixed it? Never seen a "half working" PWM unless it was the wrong PWM the first time you changed it out. Usually they either work or they don't. Hmm... have to make a mental note to that one.

[petehall347]

Re: BN44-00264A buzzing

am thinking i should have left the original one in .i only changed it for good measure when changing the fets .
i will leave it on a few hours and make sure everything is ok .
i bought 4 new chips so maybe i was just unlucky and the first one i pulled out was bad .
i re-soldered the faulty one twice hoping it was a poor joint but it wasn't .
the freeze spray led me to cp809 which i changed . the chip just happens to be on the other side of the board right under that cap .

[CapLeaker]

Re: BN44-00264A buzzing

Not sure what to say... I had plenty SMPS's going through my hands, but never had a PWM behave that way. Well... sooner or later I would have looked at the PWM output with the oscilloscope and figured it out that way.
I did have dead PWM's arrive new, but never something like that, unless it was not the correct PWM to start with. Anyway... main thing is, that it is fixed!

[dick_barton]

Re: BN44-00264A buzzing

Are you saying that it was CP809 that was faulty or the 7530?

[petehall347]

Re: BN44-00264A buzzing

Are you saying that it was CP809 that was faulty or the 7530?

the 7530 was bad even though it was brand new .
if it can happen it happens to me .. even if it cant happen it still happens to me .