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MUX not sendng BKLT PWM
- Thread starter G.Beard
- Start date
SMC_LID is OK? Does it work in SMC bypass mode? Sometimes when I get a machine with good backlight circuit, only with 0V on PWM, it starts working after I turn it on with SMC bypass (SMC/PRAM reset is not enough) and once it lights up, then it's fixed even when you normally turn it on without bypass. Had one 820-3330 (the same backlight circuit as 2915) with this issue just yesterday...
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If SMC_LID is 3.4v, and you resetting PRAM doesn't fix it, you have two choices.
1) Replace the mux on a board that will be back with a dead GPU in 1 month, when they will ask for warranty on your "failed logic board repair" that you can't provide. Make no money, deal with raging customer. 1 star review ensues.
2) Wire PP3V3_S0 to BKL_PWM. Tell the customer they need some software brightness control/contrast adjuster to deal with screen brightness. Tell them since it is not a full repair, it's on the house. Receive a refund-free tip, get a 5 star review for allowing the machine to last just long enough for them to buy a new one, deal with no warranty claims.
Greedy go for 1, I would go for 2.
1) Replace the mux on a board that will be back with a dead GPU in 1 month, when they will ask for warranty on your "failed logic board repair" that you can't provide. Make no money, deal with raging customer. 1 star review ensues.
2) Wire PP3V3_S0 to BKL_PWM. Tell the customer they need some software brightness control/contrast adjuster to deal with screen brightness. Tell them since it is not a full repair, it's on the house. Receive a refund-free tip, get a 5 star review for allowing the machine to last just long enough for them to buy a new one, deal with no warranty claims.
Greedy go for 1, I would go for 2.
I faced few times with this issue.
Don't tied to 3V directly; can affect GMUX.
Remove R9704 and inject 3V at C9704.
Next I did PRAM reset and resolder R9704; the problem gone.
This issue appears more on the machines with EFI password.
Don't tied to 3V directly; can affect GMUX.
Remove R9704 and inject 3V at C9704.
Next I did PRAM reset and resolder R9704; the problem gone.
This issue appears more on the machines with EFI password.
G.Beard
New member
I had already change the GPU for them (DC1649) and then found no PWM.... Yes, I made the mistake of not testing it first and went on customer request!
I have charged them for GPU but not for the backlight repair. Tied to 3V3_S0 via resistor.
G.Beard
New member
I just moved R9704 off of the MUX pad and wired it to 3V3_S0. I do the same with the Air boards so as not to tie CPU directly.
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G.Beard
New member
... Yes but with no PWM there can't BE any signal for the software to use to control the backlight.