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Non-booting Dell Precision 420

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First post, by r00tcz

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Hi,

I'm looking for any help trying to get this motherboard working. It's a dual CPU Slot1 motherboard with Intel 840 chipset and RIMMs.
I have all components from system that was working before, however it can't boot into BIOS. I tried all normal troubleshooting steps:
- resetting CMOS
- tried various graphics cards (original AGP card that came with the system - and confirmed working on another PC, then
various other PCI graphics cards)
- all RIMMs are correctly inserted, if not, other LED diagnostic code is given
- CPU is getting warm, also tried different CPU, no luck
Status LEDs show error code S11 that's described as completely unhelpful "Possible system board resource conflict".

Using POST code card I get following codes:
(pwr button pressed) 04 01 02 00 80 00 FE FF 3F 0F FF 3F 00 06 08 09 0D XX XX 90 00 (noticeable delay) 16 [XX values change every boot]

Since it ends with code 16 that's known as "16: BIOS ROM checksum" for Phoenix BIOS, I have ended up desoldering the Intel E8208AB that stores the BIOS
and read it with a programmer. I suspected bitrot or bad flash chip, but it seems to be working correctly, I'm getting same contents every time I read it.
Main BIOS portion of the chip is 100% identical with BIOS file I extracted from from Dell's update EXE for same BIOS version (A10), so that's not the problem.

In the dumped file, BIOS starts at 0x10000, before it are some configuration data blocks - BIOS chip dump is attached.
I can try to clean some of this data from the BIOS if that might help (IO resource conflict because of bad configuration?) but I don't like the idea of just blindly trying
different things - the chip is not socketed and it's in the TSOP package, so it's rather time consuming work to solder it back.

Any ideas are welcome...

Reply 1 of 2, by r00tcz

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Spent some more time on this, mostly disassembling the BIOS, finding where it fails:

  • The POST code 16 is not related to anything about BIOS checksum, this is custom Dell BIOS, not regular Phoenix, all POST codes are different.
    Anyone knows about list of Dell specific POST codes from P-II/P-III era?
  • Boot fails while doing something just after RIMM DEVID initialization procedure. Following function is called and it does something with IO 8C0h and 8C4h:
    The attachment func.png is no longer available
  • Anyone knows what this 8C0h device is?
    I looked into i840 datasheet, user and design guide, also ICH documents, but found nothing. In the whole BIOS initialization code there's just a few more writes to this device during early initialization and that's it.
  • I have disassembled BIOSes from other boards with i840 and RDRAM and while I can find the same DEVID initialization (it uses some unique magic words), there is no code for doing same 8C0/8C4h IO.

Reply 2 of 2, by r00tcz

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Soldered flash chip back, unmodified, only refreshed contents. Mobo is still failing to boot with the same POST codes as before - so good, at least I haven't made it any worse.
I'm starting to think this failing code might be related to SMBUS, reading something off RIMMs EEPROMs. According to RAMBUS datasheet this is next step after DEVID initialization. Don't have any other RIMMs to try.
May put logic analyzer on the I2C/SMBUS to see what's happening there... but I'm starting to run out of ideas, any suggestions are welcome.

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