Apple TV Dead Psu

[caphair]

Re: Apple TV Dead Psu

Have another with a slightly different design. I'm only measuring 1v at the main filter cap.

Already replaced fuse, diode, inductor on hot side.

[budm]

Re: Apple TV Dead Psu

I noticed ic33 has its collector tied in to the vcc of ic3

I'm curious why that's so? Is the opto being used as the voltage source for ic3? My understanding of optos are they separate primary and secondary side and used as feedback so it's making me scratch my head

What is the Emitter pin of the OPTO connected to a resistor? You can have many devices that has connection to VCC power supply so it does not mean the power is being derived through that component.
I can have for example, 10 Opto devices and has all the Collector pin connected to the VCC, the Emitter pin is then connected to a resistor on one end and another end of the resistor is connected to GND, this circuit is then configured as Emitter follower (COMMON COLLECTOR: ).
BTW, why does that red main AC line fuse body melt like that?

[budm]

Re: Apple TV Dead Psu

Have another with a slightly different design. I'm only measuring 1v at the main filter cap.

Already replaced fuse, diode, inductor on hot side.

You will have to trace the connection from the + leg to the Cathode of the rectifier, the Anode of the rectifier then should trace back to the fuse or any line filter choke back to the LINE AC input, same for the - leg of the filter cap, it should trace back to the NEUTRAL AC input.

[stj]

Re: Apple TV Dead Psu

probably a gray fuseable resistor.

[caphair]

Re: Apple TV Dead Psu

There are two smd resistors marked 106 measuring them gives 7.10megaohm. I don't see any others that could be fuseable resistors?

[caphair]

Re: Apple TV Dead Psu

You will have to trace the connection from the + leg to the Cathode of the rectifier, the Anode of the rectifier then should trace back to the fuse or any line filter choke back to the LINE AC input, same for the - leg of the filter cap, it should trace back to the NEUTRAL AC input.

So the + of the cap traces back to the + of the rectifier and the - of the cap traces back to the - of the rectifier. Is this what you mean?

Never mind there was a bad solder joint to one side of the rectifier. I'm now measuring 310v on terminals of main filter cap but the voltage gradually drops.

Also no voltages on secondary outputs

[stj]

Re: Apple TV Dead Psu

bad solder joints never happen in one's
get your magnifier out!

[caphair]

Re: Apple TV Dead Psu

Checked all soldering, everything looks fine. What should I look for now?

[stj]

Re: Apple TV Dead Psu

what's you mains, 100, 120 or 230v ?

[caphair]

Re: Apple TV Dead Psu

120v

[stj]

Re: Apple TV Dead Psu

and that 300'ish fades down to nothing?
or just to about 150?

[caphair]

Re: Apple TV Dead Psu

Haven't monitored it long enough because it fades slowly but it seemed to go down to about 290v before I stopped monitoring

[budm]

Re: Apple TV Dead Psu

Are you sure you are getting over 300VDC between the two legs of the main filter cap? There is no Voltage doubler or PFC Voltage booster that I can see on that board, it is just rectifier and one filter cap isn't it?

[caphair]

Re: Apple TV Dead Psu

There's another cap between the rectifier and filter cap. It's a maroon colored square cap. No sure if that's used for boosting? And smd components on the bottom, but not sure if those are just used to provide vcc to switching ic

I measured 320v on both rectifier +/- and on filter cap and noticed it drops to about 285v then goes back up to 320v and keeps repeating

[caphair]

Re: Apple TV Dead Psu

Whoa so I was taking voltage measurements seeing if vcc on M1 was present (which it wasn't. Only mv readings around the area)

And then R19 and R25 literally exploded and the board started arching. Traced them back and they appear to be the bleed resistors as they're connected across the main filter cap

Why would they explode like that during operation?

[caphair]

Re: Apple TV Dead Psu

I removed M1 part# 1380A

Pins 4 and 5 measure shorted. They're not supposed to be that way right? Wonder if that was the problem the entire time.

Also what do they mean by "totem pole type output"?

[caphair]

Re: Apple TV Dead Psu

Removed the bleeder resistors and with M1 removed wanted to take some voltage measurements.

Now there's a steady 170v across main filter, but the vcc pin of where M1 would be is at 75v. That doesn't make sense?

[caphair]

Re: Apple TV Dead Psu

Anyone?

[stj]

Re: Apple TV Dead Psu

probably the vcc is from the main cap though a resistor or 2 to limit the current followed by a (faulty) zener diode to limit the voltage.

[caphair]

Re: Apple TV Dead Psu

There is a zener connected to + of main cap but it measures fine (tested like a normal diode)