[help]Imac 21,5 EMC 2428 Dead

[phantom]

HI!, i've never fix an imac.

this imac doesnt power on.

i've only the first led

when i push the power button, nothing happens

power button is ok

could you help me? i don't know where to start!


thanks

 

[2informaticos]

Any histoyy available?
What is the 820-xxxx code of your board?

 

[phantom]

No history

Should I diamantle the mktherboard to check for the model?

 

[2informaticos]

Use Google at least...

Imac 21,5 EMC 2428 board - Google Search

 

[phantom]

So it should be 820-2641-a

 

[2informaticos]

U7700 is a classic issue on these machines.

 

[phantom]

so what should i check? this is the first time for me...

 

[2informaticos]

Replace it.
Be sure to solder it correctly...

 

[phantom]

without checking anything else like you teach me?!

ok i will replace it

 

[phantom]

I have 5v and 3,3 on u7700: should i change it anyway?

 

[2informaticos]

5V at L7750?
If yes, don't touch it.

 

[phantom]

I’ve 0v on p5vs3_reg_phase

 

[2informaticos]

Did you check with original iMac power supply?

BTW, remove the CMOS battery; board should start automatically then.

 

[phantom]

I have not dismantled the motherboard from the case, so it is still connected to its power supply!

It doesn bot boot without battery

 

[2informaticos]

Post U7700 basic voltages: 17, 18, 5, 4, 24, 12.

 

[phantom]

12, 5, 5, 5 3,9 5

 

[2informaticos]

Then you should have 5V at L7750.
Check diode mode to ground there.
If OK, then bad U7700...

 

[phantom]

Still the same

I have 0,144mv on pin 23 of u7770

 

[2informaticos]

Did you change U7700?

 

[phantom]

Yes but not with a brand new…i can try to buy a brand new one…what do you Think?