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486 board can't boot

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First post, by 386SX

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Hi,

I have this GMB-486SPS PCI SIS 85C496 based motherboard. I've replaced the battery and cleaned the traces, some were going to expose but I've tested and there's connection. I've set it up for 486DX Intel cpus but I've no cache of 32pin (only 4 without a tag) so I can't use it.
The point is that at boot even with an ISA vga monitor stay black. With the pci test card it show 00... some times 0... sometime it has gone further but nothing to screen.
Is the cache essential to boot or there's some problem?

Reply 1 of 14, by PeterLI

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Last edited by PeterLI on 2016-12-17, 20:41. Edited 1 time in total.

Reply 2 of 14, by alexanrs

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Try using an ISA diagnostics card.

Reply 3 of 14, by darksheer

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Wait for confirmation but I think that only 486 motherboards with fake cache chips will allow you to boot without it installed because their BIOS have been customized to counter that, else it should not boot if you don't have some or you're not respecting the specified configuration.

Reply 4 of 14, by tyuper

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Is it behaving the same with unplugged keyboard?

Reply 5 of 14, by darksheer

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tyuper wrote:

Is it behaving the same with unplugged keyboard?

Oh I make a great mistake by "boot" I was refering it as "post" in my previous answer.
A 486 motherboard without keyboard should post but won't allow you to boot if you don't have set the settings that allow it before (Like alt on : no errors) in the BIOS.

Reply 6 of 14, by tyuper

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My question was addressed to OP. 😀 Because I have the same board (DTK PKM-0033S) and it was "dead" with plugged keyboard until I replaced broken fuse.

Photo of the board with marked position of fuse.
http://i62.tinypic.com/104k9k2.jpg

Reply 7 of 14, by darksheer

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Yeah the KB broken fuse can indeed be an issue to explore as well as broken traces and bad contacts for the BIOS/cache chips but if he does not have the TAG chip installed yet, that won't change anything.

Reply 8 of 14, by 386SX

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Here I am. The motherboard don't post, nothing at screen. The keyboard lights seems to power up instantanely as usual but no effects pressing keys or whatever.

I can't see the linked photo, can you attach it here cause my browser is too old.

Reply 9 of 14, by 386SX

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tyuper wrote:

My question was addressed to OP. 😀 Because I have the same board (DTK PKM-0033S) and it was "dead" with plugged keyboard until I replaced broken fuse.

Photo of the board with marked position of fuse.
http://i62.tinypic.com/104k9k2.jpg

Or tell me the name of the component/fuse. 😀

Reply 10 of 14, by 386SX

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Ah ok I see the only fuse F1 on the pcb, is the one close to the keyboard connector?

edit: the green F1 tested with multimeter give me 0.01 ohm so I think is ok.

Reply 11 of 14, by tyuper

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Yes, this is the one. You can check it by using multimeter with ohm/continuity test.

Reply 12 of 14, by 386SX

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darksheer wrote:

Yeah the KB broken fuse can indeed be an issue to explore as well as broken traces and bad contacts for the BIOS/cache chips but if he does not have the TAG chip installed yet, that won't change anything.

But as tag can I use a single cache chip and don't put the others?

Reply 13 of 14, by 386SX

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Ah ahhhhh maybe found a broken trace! 😁

Let's see if it will (not!) work after some soldering... update soon!

Reply 14 of 14, by 386SX

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Well, it seems there're different traces broken not visibly but the multimeter can't. But they are beyond my soldering skills cause some goes to smd resistors and are really rreally thin wires... 🙁
I think I'll suspend this repair...