At 14:32 -0700 07/11/2002, Charles Baker wrote: >I recently had some low-level problems with my s900 that turned out to >be pretty serious. I troubleshooted the problem to the PCI bridge >chip, that controls/effects the bottom 4 PCI slots on my motherboard. >The computer and its components all work great except when any card is >added to the bottom 4 PCI slots, which results in the computer chiming, >but not doing anything thereafter. The chip heats up to where I could >burn myself if I touch it for extended periods, so it's obviously dead.
Is there any damage to the lower four slots or the printed circuit board around them? Does this problem occur when you only install one card in any of the lower four slots? >So my question is this: what might have caused this problem? There could be something shorting power to an improper pin on the PPB (your hot chip: DEC 21052AB). Or it could just be that the chip actually failed on its own without help. You might look around the chip for any bent pins as well. When something gets hot like that, usually power is getting supplied somewhere that it shouldn't go, and the thing most likely to cause that is an inadvertent short somewhere, e.g. pins bent together, metal shavings in the PCI slot, a scratch through traces on the circuit board which manages to drag copper from one trace across another. >I think >that it could be attributable to my overclocking the system bus >(through my XLR8 g4 ZIF) to ~57 mHz to get my G4/450 to run at 510mHz. >I know that overclocking the bus affects all components, including the >PCI bus. Actually, this isn't the case. The Bandit chip (343S0020) runs at the system bus speed (57 Mhz in your case) on one side, but at PCI speed (33 MHz) on the other side. However, the PPB (DEC 21052) runs at 33 MHz on both sides. No matter what you do to the bus speed, it has no effect on what speed the PPB runs at. So your overclocking could not be affecting the PPB in any way. To change the speed of the PPB, you'd need to replace the metal can oscillator which is just behind the PPB and to the left (or below) U45. The PCI clock comes out of that metal can (labeled 33.3333 MHz) and goes into U45 which is a clock buffer. A clock buffer takes a single clock signal and splits it out to several destinations. In this case the destinations are the Bandit chip, PCI slots 1 and 2 and the PPB. The PPB contains its own clock buffer which splits the clock signal for the four lower PCI slots. Anyway, the point is that the only clocks that are fed to the PPB come out of that metal can. The system bus is isolated from the PPB. >Another possibility that came to mind was that my card is not >the SSE edition, which obviously is fully compatible with the bottom 4 >slots. My card is the regular edition G4 MPe from XLR8 which I heard >exclusively enables the bottom 4 slots on the s900 and not any other >6-slot Apple, since it uses a completely different controller rather >than a redundant PCI controller in the non-clones from which it is >based. This shouldn't be relevant one way or the other. The SSE is only needed on machines with dual Bandit controllers. Our machine has only one Bandit and so you're better off with the MPe, as there are several reports of buginess in the SSE. >Since this is a supermacs list, I thought that you guys might know a >good place to get a replacement motherboard or whole computer for my >s900. I originally ordered this system bare-bones from poweron.com, >but they no longer offer it. I have tried the trading list here at LEM >and eBay and want to know if there is any place else (or the best >place) that I can purchase one from. I can replace the PPB on your board. I have several left over from my experiments. The only issue in my mind is whether the problem with your board is only in the PPB chip, or whether there is some other hidden cause that replacing the chip won't solve. I'd look around on the board around the PPB and lower four slots for any potential short circuits as described above. If you want me to replace the PPB I'd charge you $20 plus shipping (ship only the MB). Or if you can do the soldering, or know someone who can do the soldering for you, I can point you at a TI pin compatible replacement for the PPB which you may purchase from Digi-Key. It's about $15 plus shipping. The part number is PCI2250. If I do it, I'll use an Intel (Intel bought DECs semiconductor group) 21152 because that's what I have on hand. I've tested the TI PCI2250, Intel 21152AB, Intel 21152BA and the Hint HB1-SE33P in place of the DEC 21052 in the S900 and they all work just the same as the DEC chip. Jeff Walther Jeff Walther -- SuperMacs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | Service & Replacement Parts [EMAIL PROTECTED] | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> SuperMacs list info: <http://lowendmac.com/supermacs/list.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/supermacs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
