Phillips 32PFL4507/F7 screaming power board

[pyrohmstr]

Hi all,

I have a Phillips 32PFL4507/F7 that I got for free. When plugged in it made a super loud screaming noise. No LED, no picture. Nothing.

I spent like two months trying to fix the board that was in there but never could. Either it was too far gone or I just did stupid things to it. Either way, I gave up and bought a new board (pictures attached) off eBay. They said they tested it. It's a BA21F0F0102 5 and the one that was in the TV originally was a BA21F0F0102 2 -- but the pinouts and everything are identical.

So I installed it and it still screams. I disconnected all of the other boards and it makes less noise but it's still audible. When unplugged it drops frequency steadily for a while and then goes suddenly high frequency before going silent. (Caps discharging??)

There is a stable 8.22v on the p-on+21v pins so I'm thinking that's maybe the effect of the problem? The transformer shows about 8V AC going in and I can't measure anything on the secondary side of the transformer.

8.22v on D650,651, and 653. The caps all look really good. Not even a hint of bulging. I don't have a capacitance tester unfortunately.

Any thoughts on what to test next? If I can positively identify what the problem is I'm completely willing to try to fix this second board but if not I kind of just want to return the board and maybe throw this entire tv in the trash :c I'm on the verge or seriously giving up here. If I could know for a fact a new board or part would fix it I would throw the money but at this point if there are shorts elsewhere on the other boards I'm pretty much screwed. I hate to see these things go into landfills for want of a 1 cent part somewhere but I just don't know at what point it becomes a rabbit hole to hell.

I attached pictures. One pic of front and back with closeups in thirds. I also threw the service manual for the TV into the archive for good measure. All I have is a cheapish multimeter.

Thanks in advance for any help!

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

Forgot to attach

[budm]

Re: Phillips 32PFL4507/F7 screaming power board

Did you check the resistance of ALL the DIODES (through hole type and the SMD type) to see if any one of them show really low resistance in both directions?
Also resistance between GND and ALL+3.3V, P-ON+21V, AMP+24V.
All measurement are done with and without the main board connected to the power supply board.
PDF of the Power supply SCH from you zip file.

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

Ok! Checked all of the diodes and put the results in a spread sheet.

Important parts I think:
D102A is an SMC on my board and D102 is open. It reads 10 ohms either direction... if this is failed open could that cause this? On the original board it measures 10ohm reversed and then jumps around a lot forward. Is that something to do with the Q1001 charging from the multimeter voltage?

The other diodes all look fine. The main ones go from no resistance to open circuit over the course of a few seconds. Is that from the caps charging up from my multimeter?

Resistance from things to ground
No main board:
3.3v 13.3k
p-on-21v 20M -> .1M slowly
AMP+24 2.75k

w/ main board
3.3v 13.3k
p-on-21v 13.75k
AMP+24 2.75k

I also checked some stuff around the opto feedback
Nothing sticks out as odd - resistors look fine. Nothing open or short.
I don't know how to test the reference voltage D660 part
IC601 pin 1 has 6.7V when it should have 21.0V
pin 2 has 5.5V when it should have 19.9V

I don't want to start soldering on this because if the ebay seller wants the whole board back I'm inclined to just try again buying a different one. I'm a bit weary of losing the $50 because I tried a repair randomly. I'm also thinking this could be a common failure mode for these and all of the boards I buy will have the same problem? Any thoughts on whether it's worth it to risk the $50 - as in does this seem like something that's going to be realistically fixable?

[Diah]

Re: Phillips 32PFL4507/F7 screaming power board

disconnect the LVDS , screaming noise remain ?

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

Disconnecting everything and the screaming noise remains.

But when I disconnect the LVDS going to the display from the main board the screaming does get a tiny bit quieter. Any piece I connect or disconnect changes the pitch and volume a bit.

[Diah]

Re: Phillips 32PFL4507/F7 screaming power board

well i think you have short contact put back yours original PWB and write down the voltage you have gone to MB

tips: keep LVDS disconnected while you work till you have standby LED

you have on the service manual tips pf hearing Puzz at page 30 flow chart No.4

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

My original board is totally dead. It gets no voltage anywhere. I probably ruined it trying to fix it. I bought one of those parts kits off eBay and just bad things happened. In my screwing around I think I made everything 100 times worse. I'll call it 'learning by fire'

If I did have a short on the main board wouldn't the voltage be ok when it's just the power board alone with nothing plugged into it?

Also, if the main board is bad... could it have fried the screen when it broke initially? In your professional opinion is it worth fixing or should I just give up? I have a bad habit of throwing a lot of money into broken things that never work. I'm afraid I'll get the power working just to find out everything else is fried too.

[budm]

Re: Phillips 32PFL4507/F7 screaming power board

Just the power supply board by itself and with board connected to other boards.
What DCV do you have at AL+3.3V, AMP+24V?
You have: There is a stable 8.22v on the p-on+21v on post 1.
Screaming/squealing sound in this Two-transistor switching power supply is usually due to too much current being drawn.
In standby mode I expect the P-ON-21V and the AMP+24 to be at low level but will kick up to full Voltage when power switch is activated then the main board will send out the P-ON-H2 signal (around 3VDC).

[Diah]

Re: Phillips 32PFL4507/F7 screaming power board

as budum wrote, if original PWB totally dead, then put the one you bought, and just connect main board to it,(back light out) and on MB only the IR section connected to it, no LVDS and NO speaker.. and read voltage as requested early

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

I'll check everything and post back when I get home from work. Once too much current is drawn what typically blows first? Like, should it be sitting at 21v with nothing else plugged in?

In the meantime: is it possible that simply plugging a good powerboard into my tv could ruin it instantly in this way? Or is it likely I bought a bad board in the first place? I don't want to be unfair to the eBay seller if I'm the one that broke it.

[budm]

Re: Phillips 32PFL4507/F7 screaming power board

When too much current is demand from this power supply design, it will usually damage lots of parts in the drive circuit in the primary side.
There are lots of thread in B.C about these EMERSON/MAGNAVOX/PHILIPS power supplies.
As you can see, they sell power supply repair kits:
http://www.shopjimmy.com/catalogsear...=BA21F0F0102+2

[Diah]

Re: Phillips 32PFL4507/F7 screaming power board

early to make judgment, as you had now 2 months working on it, the cable which go from PWB to MB are slide one, you need to inspect it if one of the print pint moved to side, as it may dried as age of Tv and this can easily happen

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

Thanks for the help so far! I should have posted here sooner instead of being stupid with my first board.

With nothing connected:
p-on+21v 8.24V / .3 Mohm
AL+3.3v 3.35V / 13.3 kohm
AMP+24v 9.62V / 2.7 kohm

With the MB connected and the button board connected to that
p-on+21v 1.04V / 13.8 ohm (betting this is a problem :p)
AL+3.3v .51V / 11.65 kohm
AMP+24v 2.22V / 2.75 kohm

Anticipating the next questions to be measure the resistance on the MB with nothing else connected:
p-on+21v 5.2 ohm
AL+3.3v 103 kohm
AMP+24v either open or out of range for my DMM (>200Mohm)

I attached photos of my MB. Is this evidence the power board is (probably) good? I'll start following the p-on+21v rail on the schematics and see what I can (maybe) find. What do y'all think?

[budm]

Re: Phillips 32PFL4507/F7 screaming power board

"p-on+21v 5.2 ohm" I think you found the problem.
Is this your board based on what is printed on the sticker?
http://www.shopjimmy.com/philips-a21...-main-cba.htm#
'A21F5MMA-001'

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

Well... is there anything to be done here or am I barking up an improbable tree of finding the problem?

I've been tracing the 21v rail but short of lifting each part and seeing what happens is there anything I can do?

Or should I just throw in the towel and buy a new MB?

[budm]

Re: Phillips 32PFL4507/F7 screaming power board

It is not going to be easy without the diagram since that 21V can spread into many directions of the board.

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

The service manual has the schematic... do they have boardview files for these boards like they have for macbook motherboards? I realize that's probably a dream lol

I guess I'll mess around with a bit and see what I find. It looks like it primarily powers the 1.2V reg, 3.3V reg, and 5V reg. I'll report back if I find anything interesting!

Yes, that shopjimmy link is my board exactly. I guess if all else fails I can get that! I'm afraid it'll just have something else wrong though :/ like my luck will be a dead backlight or something too

[CapLeaker]

Re: Phillips 32PFL4507/F7 screaming power board

I had a look at the backside of the PSU. I see that the 21V is spreading around the board like budm already said. However there are jumpers. I would remove one leg and try to find the section that has the problem. You know that the 21V has a short to GND. So it has to be a component (transistor or diode) that is connected to GND.

[pyrohmstr]

Re: Phillips 32PFL4507/F7 screaming power board

I think I found something!

I removed all three voltage regs on the MB and it was still shorted. Then I randomly removed C3103 by the 1.2V reg and the short went away. Up to ~10Mohms on the p-on+21v rail.

But, I left C3103 off the board. Does it do anything critical? It's near the 1.2V reg on page 51 of the service manual. If it's just a filter or something can I survive without it? .

Secondary problem: the TV still will not turn on. From the schematic it doesn't look like it has a standby LED - just a power on white LED with no dual mode or anything. Pressing the power button or the remote gets nothing. The whine is a lot quieter now even with everything (LCD + BL) plugged in.

When it's plugged in and sitting p-on+21v is still at 7.82 and amp+24v sits at 9.8v while al+3.3 is at 3.3v

Thoughts?