820-2879 board, ppbus_g3hot 12.6v then goes down to 6 and get back again

[turbo]

got this board, 12.6 goes down to 6 then goes back again,

 

[dukefawks]

Check sense resistor circuits for ISL6259

 

[turbo]

isl pin 27 and 28 getting 16.11v, , ...

 

[turbo]

last 2 hrs working on it no luck... still same, ppbus getting 12v stay there 3 sec then it goes down to5v and come back again,, also i notice r7086 pin goes to 6v stay 2 sec, then goes back to 15v

 

[turbo]

if you chk the video, you will see what is ppbus doing https://www.youtube.com/watch?v=OlUh_lpu_bI

 

[JorgePayar]

Do you have the same problem if you connect it to the battery?

 

[dukefawks]

Remove F7040 and check again. Also measure resistance over C7020 and C7050.

 

[turbo]

i already remove , F7040, thats the first thing i did, also chk resistance, open line between c7020 and c7050,... resistance between 2 pic c7020 is 20 ohm, c7050 3 ohm

 

[aprendiz]

Check R7005, should be 20ohm, if it is bad replace ISL6259 and R7005 together.....

 

[turbo]

r7005 is 20 ohm, put new isl still sale problem !!! any help from any one ?????????

 

[JorgePayar]

r7005 is 20 ohm, put new isl still sale problem !!! any help from any one ?????????

I asked you a question before, do you have the same problem if you connect the battery? (battery alone and with charger as well)

PS: still waiting for your resistance measurement about 820 2850 thanks

 

[turbo]

with the battery ... it has constant ppbus

 

[JorgePayar]

with the battery ... it has constant ppbus

Ok check q7080 for corrosion, q7085 it appears to be fine but check it as well that is my bet

 

[turbo]

board turn on now.... fan spin regular speed, no doooooooong or it does not boot... even with external monitor no video..... when i turns it on front led of mac keep on.... sorry about my bad English

 

[larossmann]

If CPU vcore and MCP vcore are present, my guess is dead MCP89.