VOGONS


First post, by jcarvalho

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Hello to all, I have an unbranded 486 motherboard that by bios string is an Jetway/JetBoard/J-Mark J-446B, here is the link: http://motherboards.mbarron.net/models/486pci/j446b.htm
MB manual

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j-446b.zip
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160.17 KiB
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60 downloads
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motherboard manual
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Fair use/fair dealing exception

It come with fake cache chips 😠
I have installed an Enhanced Am486DX4-S @ 120 Mhz
I have ordered 4 chips w24512AK-15 in order to have 256Kb + W24M257AK-15 for tag ram.
the machine hangs on screen after detecting hard drives... What am I missing??
Looking on manual 19, it shows the jumper settings only for 128kb and 512kb. I have tried all combos but no luck, even with tag ram pulled out
Thanks,
Jorge

Reply 2 of 9, by jcarvalho

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Yes!! It boots and runs very nice! No stability issues... I have left this baby running more than 24 hours in a row.... With L2 cache disabled... Now with cache enabled it hangs on Paralel Port(s): 378
And I disabled serial and parallel ports 😲 on chipset features setup screen

Reply 4 of 9, by jcarvalho

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kixs wrote:

Did you correctly installed the chips? That 512KB cache in the manual looks like a typo.

can you explain better? I tried the 512kb config and 128 config. Could be the tag ram? I use a more ram chip w24m257ak-15
Part #: W24M257AK-15
Part Category: Memory ICs
Manufacturer: Winbond Electronics Corporation America
Description: 32KX8 STANDARD SRAM, 15ns, PDIP28

Reply 6 of 9, by jcarvalho

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Hi guys! I think that I have found the problem.... Those MB makers removed the pin 28 from the tag ram socket. Looking in the datasheet IC is the VDD, 5V power pin 😠 Because of the fake cache/tag ram chips... Now I am removing the old socket, solder a new one and test it... More news to come...

Reply 7 of 9, by jcarvalho

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Hi Guys! Quick update... Now the motherboard is working very nice. It was in fact a pin socket removed from factory... Desoldered the old socket, placed a new one, fitted the tag ram in position and it works flawlessly!!! Nice work Jetway/JetBoard/J-Mark for selling crippled motherboards... May be this problem could be applied to other "cheappo" motherbords or unbranded ones. It worth a try to have a look to the socket in order to put them "full specs"... BTW, is there some other mod that I can do to improve the motherboard?
Thanks,
Jorge

Reply 8 of 9, by TheMobRules

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Nice! That will definitely be useful for others who unfortunately have fake cache in their retro PCs!

I'm still amazed at how those motherboard manufacturers got away with this... total impunity! Imagine if a car manufacturer would sell models with engines featuring a couple of "fake cilinders"! 😁

Reply 9 of 9, by smolotov

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Hey Jcarvalho!
Now six years later and I'm having the same problem with my 446 board. It takes 33Mhz and 66Mhz chips, but no 120Mhz ort 133Mhz AMD 486's. It was indeed stuck at boot with a blinking cursor at the LPT port on the bootscreen.
I stumble upon your solution, and guess what? It also worked for my board!

I didn't remove the entire socket though but I removed one pin from a socket on a donor board and carefully soldered that in in the existing socket on the 446 board. It now boots perfectly with a 5x86 133Mhz.
And so, even years later, your help is appreciated. So my thanks.