Macbook 820-3536A Problem

[mrtutz]

Update. I'm not sure if I should start a new thread asking these questions in the laptop fault finding section of the forum, so apologies in advance if I'm asking technical questions in the wrong place.

I carried out some further checks on the logic board and a couple of things are not making much sense to me. When I measure for a short on PP5V_S4 I get a relatively low reading, around 9 ohms. I also don't have an enable signal into U7501, which I have traced back to a missing signal from the CPU on PM_SLP_S4_L.

I removed U7501 with my hot air station, and the resistance increased slightly to 14 ohms. I also removed L7520 and U7520 and the low resistance in the circuit seems to be on the output side of L7520.

Am I right in assuming that 14 ohms is too low a resistance on PP5V_S4? Would a short to ground prevent PM_SLP_S4_L?

I did inject 3v at 1amp and checked for anything warming up, the only thing was U7501.

Can anyone give me a point in the right direction?

Thanks in advance

[mrtutz]

Re: Macbook 820-3536A Problem

Sorry. Posted on the wrong thread before. The history of the machine:

It came to me as a complete, spares or repair unit. No evidence of any water damage. All of the S5 rails in the laptop are present. The charger light turns green when connected, then turns orange.

[zpi]

Re: Macbook 820-3536A Problem

Hi, to be sure you don't have pm_slp_s4_l, you should check for spike with oscilloscope when turning on.

But 9-14ohms are short on 5v_s4 rail. Definitely first need to fix this to expect stable s4_l.

You said you removed L7520 and short is on output. So you should inject 1v on L7520 Pin1 (Pin one is output here) and check amperage and find hotspot on board, Thermal cam is a big helper here, even a cheap one. Because you can find even a small short with one Volt and only few degrees hotter spots. But as you have about 10 Ohm short, you should easily find it with your fingers.

Also please explain: You said U7501 was warm and you removed it, but you still have short here ?

[mrtutz]

Re: Macbook 820-3536A Problem

Hi Zpi.

Thanks for responding. U5701 was very slightly warm, it wasn't burning my finger. Unfortunately I don't have a scope, or a thermal camera as of yet, so I will do as you suggest and spray the board with alcohol to see what gets hot that way.

I will let you know what I find.

[mrtutz]

Re: Macbook 820-3536A Problem

Update. It looks like this board has been worked on before. U6201 is missing completely from the board, DZ6606 has blown, and burnt out the tracks close by.

Looks like this one is a parts only board now.

Thanks for your help.

[zpi]

Re: Macbook 820-3536A Problem

Upload photo, maybe its still fixable.

[mrtutz]

Re: Macbook 820-3536A Problem

Hi zpi.

See attached images. They're not the best but will hopefully be OK. I ordered a replacement logic board from Aliexpress, which should arrive in 20-40 days. I would still like to attempt to repair this board if its possible.

[zpi]

Re: Macbook 820-3536A Problem

Board can work without this chip, its sound card, those contacts near headphones also looks like they are for headphone jack. Try to find heating elements on board when injecting voltage to l7520.

My bet is that U6201 was removed because it had hole in it, because it is driven by 5v_s4, you should find shorted cap while injecting voltage, and board will work