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820-00291 iMac 27" 5k 2015 no power

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lincev

Member
Hello I have this board but it does not receive power, I have tried another power supply but at no time does it turn on the LED1 if I have some voltages on the pins of the board that has the 12v supply connector. I do not have a schematic of this board and I have not been able to find it.

I wanted to ask if I can check any fuses and get lucky.

thanks for all
 
L

lincev

Member
Hello I have

PP12V_S5= 12.04v
PP3V3_S5= 0.0v I have measured at different points to check and none have tension

very very thanks for schematic
 
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L

lincev

Member
I have not tested, as the LED1 does not turn on I thought it was a short circuit problem or a burned track. Did you change the thermal paste to the processor?
 
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2informaticos

2informaticos

Administrator
Staff member
Do NOT quote an entire post visible few centimeters above.
Please, maintain the forum aesthetic.

Lift L7610 one side and see where the short remains.
 
L

lincev

Member
sorry I have had a lot of work and I have not been able to do this last test. The problem is now I was about to check this and recheck in diode mode to make sure which one was failing and now the two components give me a short circuit ... I don't understand anything ... it is possible that the other day I did not go through some voltage residual?

Perhaps it has spoiled being on the table? hehehehe

Do I still do the test you told me or do you want me to try something new? Thank you
 
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lincev

Member
Hello I tried again (after a few days without electrical current) and in diode mode both components L7610 and L7650 short (beep).

If possible, continue to help me. Thank you very much
 
2informaticos

2informaticos

Administrator
Staff member
Lift one side the coils and see where the shorts remain; also post exact ohm values.
You didn't have short at L7650 before, what happened???
 
L

lincev

Member
Ok I do this test with L7650 (at the moment I do not have a soldering iron and it is impossible for me) I will comment on the results.

Last time maybe in the rush I was not touching the component correctly to measure a short and from the beginning both components were short.
 
L

lincev

Member
hi again, I change L7650 and this is fix don't have short. But L7610 I have a short with Pin1 3V3_S5

i have short in C7670 C7671 C7674 C7676 (value 0 mode diode beep)
 
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2informaticos

2informaticos

Administrator
Staff member
Change the coil???
Impossible to have short to ground because of a coil into a buck-converter; the coil does NOT connect with ground.

I said to lift ONE pin of a coil and check which side the short to ground remains.
 
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lincev

Member
Sorry for my English that there was no presence of continuity in the coil.

I have lifted L7610 and I have the short to ground on Pin 1, I have checked the capacitors and at those points of the track I still have the short so the problem must come from a previous component
 
L

lincev

Member
I have connected the power supply and I have measured in several points of Q3771 U3781 or C3781 and I only have 0 value.
 
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