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external cache woes

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First post, by retro games 100

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Problem overview: if the mobo BIOS external cache setting is enabled, mobo hangs on it's POST activity.

Mobo: Acer AP43 (486 PCI), SIS496 chipset.
http://stason.org/TULARC/pc/motherboards/A/AC … C-486-AP43.html

Cache: it's been jumpered for 256k, but I don't know how to check (verify) how much cache I have on the mobo.

Testing: if I set the BIOS to "optimal setting", and also manually edit the external cache setting to disabled, then the mobo boots up successfully. It's only when I edit the external cache setting to enabled, that the mobo does not boot up successfully.

When I set the external cache to enabled, I also set the cache mode to write thru (not write back), and leave the tag width at 8 bits (not 7 bits).

Looking at the board, I see 2 cache banks. Each bank can hold 4 chips. 1 bank is full, the other bank is empty. So, there's 4 cache chips (and also 1 tag chip.) Each of the 4 cache chips occupy their entire socket space, but the tag chip is "2 notches" short of occupying it's entire socket space.

The 4 cache chips has this writing on them -

UM61512AK-15
9603G
MB2419

The tag chip has this writing on it -

W24257AK-15
95461

Looking at the mobo specification (please see link above), there are 5 cache configurations to choose from -

128KB
256KB (A)
256KB (B)
512KB (A)
512KB (B)

The board is currently jumpered for 256KB (B). I wonder if other BIOS settings are not cooperating with this cache configuration, or one of the cache chips is faulty. I would really like to mess around with any BIOS options first, before I start pulling out chips...

Any comments very gratefully received. 😀

Edit: I got the chipset a bit wrong. Sorry. There's 2 chips on the mobo, 1 says: SIS 85C497, the other chip (of a similar size) has a hand written sticker on it that just says: 21932. The mobo is AMIBIOS, but the interesting thing is that on POST, it displays some kind of revision update of feb '96, which seems quite modern! Lastly, inside the BIOS, there's an "engineer mode" which lets you mess about with memory and cache timing, but as I don't know what I'm doing, I just left the settings "as is".

Reply 1 of 7, by retro games 100

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I tried using my POST test card, and I get this error code -

A3 A2

I check AMIBIOS error codes, and I see -

A3 = The soft error display has completed. Setting the keyboard typematic rate next.

A2 = Displaying any soft error next.

(BTW, A4 = the keyboard typematic rate is set. Programming the memory wait states next.)

Reply 2 of 7, by retro games 100

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When I change the BIOS external cache setting to enabled, and then reboot, I hear 3 beeps being played repetitively. I check my beep code table for AMIBIOS, and I see this -

Base 64K RAM failure.

Does external cache rely on what type of RAM you have? ATM, I have 1 16mb stick of Kingston RAM. It seems to work OK, but not it seems, if external cache is enabled. (I think it's non EDO. I don't think this board accepts EDO RAM.)

Reply 3 of 7, by Shodan486

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All of us know that you have piles of other mobos, so try to pull out some cache chips from one least beloved and try them with this one - this is a fine mobo, not to say it uses SMT technology for most of the parts, but I plan to buy this one in future and need to know what problems await me ahead. So, swap 'em!.

MOBO: PVI-486SP3 Rev 1.2
CPU: POD-83
RAM: 2x16MB
VIDEO: Matrox Millenium 2MB/Voodoo2 12MB/Video Blaster VT300
AUDIO: SB Vibra16 FM
SCSI: 72GB 15k RPM HDD/YAMAHA CD-RW 16x/ZIP drive + FDD drive
NIC: 3Com Etherlink III
PSU: 230W Generic
OS: Win95 OSR2.5

Reply 4 of 7, by luckybob

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UM61512AK-15 is a standard chip. 4 give you 256kb of cache and 8 give you 512. hence the 512 in the part number. as for the jumper settings, the first 256k option is for EIGHT chips TOTALING 256k. the 2nd is for 4x 512 chips for 256k. #3 would be EIGHT chips for a total of 512k and #4 would most likely be 4x 1024k chips for 512k.

256k chips are 2 pins shorter than 512 and 1024 bit chips. "usually" having 2 banks of the larger sockets means you can upgrade to 1meg of cache.

I would go ahead and reseat all the chips you can. just put them back where you got them!

Once men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them. - Reverend Mother Gaius Helen Mohiam

Reply 5 of 7, by retro games 100

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Please note that my o.p. was in June 2009. Unfortunately, I can't remember what happened to this mobo. Thanks a lot for the info about mobo cache.

Reply 6 of 7, by luckybob

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say no to zombies! thanks shodan486... 🙁

Once men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them. - Reverend Mother Gaius Helen Mohiam

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