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Asus P/I-P55T2P4 does not work and throws memory errors

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First post, by amauget

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Greetings to all,

I recently acquired an Asus P/I-P55T2P4 v3.10 motherboard equiped with a Cyrix 6x86L-P200+GP CPU but no RAM.
I bought 5 pairs of EDO stick (16 Mb and 32 Mb). I put a PCI VGA card (ATI Rage XL) and fired the mobo up.
Of course, the CMOS battery has dried up, as the posting screen mentions
MEMKEEB_t.jpg

The first thing I noticed was the BIOS setting weren't saved. Then I launched Memtest86 2.01+, it crashed immediatly :
MEMKEEC_t.jpg

After using the clear CMOS jumper, Memtest86 2.01+ launched but crashed with an Unexpected Interrupt error :
MEMKEEE_t.jpg

Then I switched to Memtest86 3.2. It launched flawlessly but report tons of errors :
MEMKEEG_t.jpg
MEMKEEI_t.jpg

I cannot boot MS-DOS : the boot starts but crashes at an early stage, without any message. So I can't flash the BIOS.
I have no way to test the CPU and RAM on another motherboard. I've tried all the the pairs of EDO sticks, same problem. I changed the PSU to no avail.
I change the jumpers :

  • Voltage regulator from 2.9V to 2.8V
  • Bus frequency from 75 Mhz to 66 Mhz
  • Bus frequency from 2.0x to 2.5x

I inspected the motherboard, no signs of damage.

I'm almost stuck right now. Reading the manual carefully, the CPU doesn't appear to be supported. But the seller says everything was working before the mobo was put away years ago.
Did I miss something ? Does the motherboard requires a new CMOS battery to work correctly ?
Thanks a lot.

Reply 1 of 4, by Repo Man11

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There could be more than one thing wrong, but I've seen enough flaky behavior when it comes to flat CMOS batteries that I don't see any point in continuing troubleshooting efforts until you're replaced that battery.

"I'd rather be rich than stupid" - Jack Handey

Reply 2 of 4, by TheMobRules

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One of my ASUS boards would have a really erratic behavior until I modified the Dallas chip to use a coin cell. It seems that when the battery is low it refuses to save the CMOS settings, leaving things in an inconsistent state.

So yeah, definitely try a fresh Dallas chip (or mod the current one), reset the settings and it should work. You may also want to try a regular Pentium if you can get one (they are very cheap).

Reply 3 of 4, by amauget

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The RTC is not a Dallas 1287. It's a M48T86PC1 which seems to be pin compatible. Without desoldering anything, I've tried the the CR2032 mod anyway but haven't found the original battery connections.
MEMTD15_t.jpg
MEMTD16_t.jpg
MEMTD14_t.jpg

And now this is worse : the mobo doesn't boot at all. In fact, the PSU doesn't seem to start anymore, as if there was a short somewhere. I think my next move will be to desolder the RTC add see if I can't get the mobo to boot again...

Reply 4 of 4, by shevalier

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amauget wrote on 2023-07-14, 16:12:

The RTC is not a Dallas 1287. It's a M48T86PC1 which seems to be pin compatible. Without desoldering anything, I've tried the the CR2032 mod anyway but haven't found the original battery connections.
And now this is worse : the mobo doesn't boot at all. In fact, the PSU doesn't seem to start anymore, as if there was a short somewhere. I think my next move will be to desolder the RTC add see if I can't get the mobo to boot again...

Somewhere from internet
h_1396586386_6796878_d6bd153f85.jpg
h_1396586386_1087266_d0ed7741bf.jpg
h_1396586387_6103831_5950b025e8.jpg

or this
https://www.zonadepruebas.com/viewtopic.php?t=3235
or
37275.jpg

Aopen MX3S, PIII-S Tualatin 1133, Radeon 9800Pro@XT BIOS, Diamond monster sound MX300
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