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820-2879-B a returning continiously beeping

L

LaptopRepair

Member
I got the MCP from the leverancier, soldered and tested the resistance on the PP3V42 to the ground, Now it is very hign almost 95K.
The mac does not beep anymore, the fun is spinning after pressing the power button, but so beeld is showing up.

By coincidence I touched the ISL9504 and I burned my finger. Directly I ve shut it down. I am afraid that this ISL is short, how can I test it if it is?
 
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Gurmon

Gurmon

Member
So now U7400 is heating up, probably due to at least one or more Q7400-03 Mosfets being shorted. If this is the case a very high chance the CPU is dead.

Have you measured resistance/diode on L7400 & L7401 ?

I really think this will be the end of this board unless your determined to pour more hours into this.
 
D

dukefawks

Administrator
Replace the ISL9504. Usually when they heat up this was because of a spike on the 5V line that killed it. But if I'm honest here just trash this board it was a time waster from the start.
It beeped before touching the MCP so the ISL9504 was working fine as the CPU needs to work for the system to be able to beep.
 
L

LaptopRepair

Member
Thanks guys for your support till so far. To me the time and money that I am investing on this board is lucrative and beneficial, because while doing it I keep learning. The option to through this board in the thrush will not helps me understand more. To others the situation maybe it is not and I can fully understand.

Back to my problem.

After looking to the circuit around the U7400, I ve found the Q7403 was short to GND. I ve replaced this one and Q7402 and now the U7400 is not hating anymore.

But still no image on screen.

After doing some measurement I ve found that no PPBUS_SW_BKL is appearing on the C9712. This leaded me to look for where this has stopped. PPBUS_SW_LCDBKLT_PWR must be generated by the Q9806 if PPBUS_S0_LCDBKLT_FUSED is present and the gate is low. After measuring PPBUS_S0_LCDBKLT_FUSED was present ~12V but the gate signal (LCDBKLT_EN_DIV) was high ~10V. This is supposed to be ~4V.

LCDBKLT_EN_DIV to have that low value the FET Q9807 need be activated by the presence of a high value of the LCD_BKLT_EN. This signals is unfortunately coming from the MCP.

According to my analyse above will this mean that this MCP has another problem then the original one?
Because before soldering it on the board I ve asured that the RTC cuircuit was not short to the GND by measuring.

Or you guys you can see something else?
 
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J

Joesipaq

New member
Sorry this isn't an answer - But I want to say good on you. I have had a few times where I just want to keep hammering away on a "throw it away" board. I don't just want to get "Bro" solutions from this forum either. It does frustrate me when the people helping me are beating me down telling me that learning more in depth and experimenting/trying to come to a solution from beyond the normal level of repairs - Has less value than a trash can sitting next to me...
Keep it up LaptopRepair, I hope you have success on this board.

On a side note, I do agree with a few thing said - All the MCPs that you can buy are pulled from another board. Why? Who knows... as Duke said, around 50% what you will receive will have an issue with them. There is an extremely high chance that the replacement you received is a bad one - and it might have failed/been failed in a way that could hurt other parts of the system.

Once again, good luck and keep sharpening the best tool there is! Your brain.
 
Gurmon

Gurmon

Member
Its not that we are trying to put you off, we have all been here in the past. These are the wrong boards to practice on, since its nearly always the MCP. Its been YEARS since you could buy a MCP with some confidence it will work.
Trust me we have tried.
If this was a backlight/usb/vcore problem there is some hope. But an issue like what your board has its truly hopeless. There is nothing to gain other than to learn when its time to stop.
 
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