Mdd 1.25 cpu fried! MDD motherboard/cpu compatibility?

W

Windsong

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I've just finished (after much help from folks here) diagnosing what's wrong with my MDD. Replaced PSU, motherboard good...
FRIED CPU.

My Logic board is marked 820-1476-A. I found a good used dual 1.25 CPU pulled from a MDD motherboard that's labeled (the label on the motherboard) 820-1472-A.

The seller (not a mac guy) can't tell me if his dual 1.25 CPU will work with my motherboard, the numbers are close, but not exact.

ANYONE know if the motherboards are compatible, i.e. if a cpu pulled from that motherboard will run on my motherboard?

If noone knows, any ideas where I could find that info?
From my research so far, some MDD motherboards with nearly similar numbers CAN interchange CPU's, others cannot.

ANY help appreciated, especially now that I've got the issue isolated.
Nobody's selling motherboards WITH CPU's, everything is being parted out.
Thanks.
Tom
 
You'll know if its a dual, instead of having ONE (small square that looks like a mirror) it'll have two of them. the MDD should have enough space on the board to run a dual, but you'll have to get the correct heatsink.
 
And there all pretty much compatible, You could even put the 867 from a MDD and it would work.
 
Thanks Jesse,
Yes it's absolutely a dual 1.25 , same as mine.
The heat sink from what I can tell, looks a bit different. That's not my real concern.
But I did read in one of these mac forums, that ROM instructions and other "stuff" on the motherboard make some revs compatible and some revs not.

You're saying with motherboards that close in part numbers, it should work?
I still have my heat sink and the "new used " CPU comes with it's own.

Looking at the picture the cpu's are identical in every way I can tell (holes cutouts) and exact shape , so I'm sure the processor will fit. The heat sink seems to be an upgrade from the one I have.
Mine is like those baseboard heater fins... thin thin sheets of "metal".

The new heat sink has what looks like fewer, and MUCH thicker (possibly aluminum?) fins.
The pic doesn't show how it screws down. It may, or may not fit from what I can see.
But if the processor fits & will work. I'll just use my original heat sink.
Tom
 
Well, The thinner ones were said to trasfer heat better, more thinner fins.
The heatsink is held down by metal clips, that goe in between the heatsink, and grab on to the processor, You can easily remove them, by taking a flathead screwdriver and rotating it. The processor itself is held down by 3 screws, after that, it pulls off easily, ALL PowerMac processors have the same 3 screws, some just vary in board size.

If you are in fact buying a Dual 1.25, and you had a Dual 1.25 that went out, it will work for sure.

It will fit.

=]
 
Thanks... your post in the other thread, however has me swallowing with a lump in my throat. ("many many other things..." [could have blown]).

I see about the thinner fins being better. Actually my heat sink screws on with five screws. No clips.

OK, so I'm really freaked out now...

I need a MDD (for the sake of an entire MOTU hard disk recording system with a breakout box AND a PCI interface card that ONLY fits and works in the old G4 PCI slots among other issues).

With the processor selling at fixed $114 shipped,
and a used MDD (dual 1.25) entire machine from a tech place with a good rep selling in the $195-$205 range shipped,
I'm thinking I probably should blow my entire upgrade budget and just get the whole darn machine.

Needing to use macs, and being "financially challenged" DO NOT go well together...
Tom
 
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Sujanne,
Welcome!
For the folks here to help, we need more specifics.
What model you have, as much info as you can give on the basic system you have. You can get a lot of it if you don't know from "about this mac" which is one choice in a dropdown menu from the apple in the upper left corner of your screen.
Once you've described your basic system (including the amount of RAM, Hard drives, how old the computer is, and which version OSX you're running...) , let us know when this started happening.

The first step is diagnosis is much like going to a Dr.
When did it first happen?
Had you added or changed anything in your system prior?
Or had nothing changed, and out of the blue this boot problem started happening?
Think about when it started.
When you say "the green light", you need to be more specific.
Some monitors have a light that comes on (green blue, others) when the monitor is powered on, no matter what.

Some monitors flash if they don't sense a signal, some flash upon startup, and then glow steady. Mine simply has one blue light. If the monitor is plugged into the wall and I turn it on, the blue light glows. The light has nothing to do with the system booting or not. If my monitor is on and the system isn't sending ANY video signal, I see the words "digital, analog" flashing on the screen. It's trying to sense if any video is coming to the analog connector or the digital connector.
If the the screen goes from off to plain gray, that means trouble for me.
I DID have a monitor that flashed if it could NOT find a good video signal coming to it, but we have to know what "normal" is for your monitor.

The most meaningful info you provided so far is that sometimes the system, when left, starts up after a while.
I'm pretty sure that's where the experts here will focus their attention first.

Try to give us a bit more. If it does boot after a few minutes, does the system operate "normally" after that, until you turn it off?
Or does it eventually "go all wiggy".

I'm fairly certain you'll get helpful replies as you give the community more to work with.
Also, it's fine to start a new thread and title it something like "System Won't Boot, red light on motherboard steady... help." and then describe the system and the problem as I suggest above.
In my case it was first, a dying power supply (I replaced it), which may have fried the CPU. I'm awaiting a used motherboard AND CPU. I won't know which went bad until I switch them.

Generally the steady red light means power is getting to the motherboard. But there still may be other issues. It could even be disk corruption and not hardware related. Do you have any disk utllities such as Disk Warrior or Tech Tool Pro?
One last Q: does the screen flash or show anything when it's trying to startup (when it manages to start afer a few minutes "by itself")? A flashing mac icon? A flashing floppy disk icon?
Tom
 
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