Dead Early 2008 MacBook Pro 15"

[AStrutter]

TL;DR: MacBook with a G84-603-A2 doesn't start and shows typical symptoms associated with GPU failure. I replace it with another board which also has a 603 and shows the exact same problems. What to do now?

Hi,
I recently got a MacBook Pro 4,1 - A1260 for free, and even though I don't really need it for anything, it pains me to see such a good-looking machine not work, so I would like to try and fix it. Here's what my experience with it has been so far:

When I got the computer, as soon as I plugged it in, it would turn on on its own, but it would just stay on a black screen, no chime, fans spinning, and only the power indicator on the front lit up. After trying a bunch of stuff, I discovered that these kinds of symptoms are commonly associated with a dead GPU, very common failure for this model, so since I'm no expert at soldering I decided to just order a "new" logic board on eBay after I found one being sold as 100% working.

When I disassembled the machine to replace the board, I noticed something weird: the logic board that was originally in, actually already had a "fixed" GPU, a G84-603-A2 with a date code of 2012, and I noticed it also had the green dot sticker on the ram slot meaning Apple had already worked on the GPU. Still, I replaced it with the board I ordered: this one has a 603 with a date code of 2008 and no green sticker.

I reassembled everything and guess what? Same exact problems, literally. Right now, I feel like there's only two possible explanations:
1) Somehow there's something else wrong in the computer that prevents it from starting.
2) With my usual luck I managed to come across 2 failed G84-603s which are supposedly pretty reliable.

At this point, I'm asking for your help: is there something else I could try to do now? Personally, I have two suspicions on what could be the other issue, but information is pretty scarce, so I don't know if these could actually be causing the problem:
1) The MacBook doesn't have a battery and the charger I'm using is third-party; maybe it doesn't like the combination of the two things?
2) The original board that was in the computer didn't have a PRAM battery connected, and if the one that came with the board I ordered is as old as the board itself, it is most certainly dead; I personally never came across a computer that doesn't work at all if the PRAM/CMOS battery is dead or removed, but with MacBooks you never really know.

I'm open to any suggestion, so if you have any hypotheses, please share them. Thanks in advance.
(Sorry for the long post, but I really wanted to get all the possibly relevant details out)

 

[AStrutter]

Well, apparently I figured out the issue: when I got the computer, it had two sticks of 2 GB of RAM at 800 MHz. At the time, I didn't think it was an issue since I knew that the T8300 had an 800 MHz bus speed. Today, while I was checking the EveryMac page for this model in search for potential clues, I noticed that the specs said it came with 667 MHz RAM, and that gave me an idea: I dug out a random stick of 667 MHz DDR2, put it in and, wouldn't you know it, it started up just fine and went to the "no OS" screen (which was to be expected since the hard drive had been emptied).

I guess today I learned that it's usually better to check the simplest things first...
I'll leave this out here in case anyone else comes across a similar issue.

 

[TheShortTimer]

I guess today I learned that it's usually better to check the simplest things first...

We've all fallen victim to this and kicked ourselves for overlooking the most (on reflection) obvious possibilities.

I'll leave this out here in case anyone else comes across a similar issue.

Thanks for doing so. It's always helpful for others.

 

[rampancy]

Well, apparently I figured out the issue: when I got the computer, it had two sticks of 2 GB of RAM at 800 MHz. At the time, I didn't think it was an issue since I knew that the T8300 had an 800 MHz bus speed. Today, while I was checking the EveryMac page for this model in search for potential clues, I noticed that the specs said it came with 667 MHz RAM, and that gave me an idea: I dug out a random stick of 667 MHz DDR2, put it in and, wouldn't you know it, it started up just fine and went to the "no OS" screen (which was to be expected since the hard drive had been emptied).

I guess today I learned that it's usually better to check the simplest things first...
I'll leave this out here in case anyone else comes across a similar issue.

On paper, PC2-6400 DDR2-800 RAM should downlock itself to 667 Mhz and work perfectly well when it's either (a) installed with PC2-5333 DDR2-667 RAM on a system that uses DDR2 667 Mhz RAM or (b) installed by itself on a system that uses DDR2 667 Mhz RAM.

In reality, I've found that results can vary wildly (and yes I've done tests on different machines using the same RAM). I've used DDR2-800 RAM in MacBooks and MacBook Pros all the way from the 1,1 to the 2.0 Ghz MacBook 5,2 and the MacBook Pro 3,1. Sometimes they'll work mixed with DDR2-667. Sometimes they won't. Sometimes they'll only work if I'm using all DDR2-800. Sometime they simply won't work at all. It's really weird.