VOGONS


First post, by mac57mac57

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Hi, I purchased a 386DX/33 motherboard from eBay and built out a fully operational bench system on it - "bench system" meaning that I assembled and connected all the parts on a workbench vs. in the case. Now I am ready to move the finished product to the intended case. However, as I reviewed the hookup of the various case lights and switches to the motherboard, I quickly realized two things:

1/ The motherboard document that I have and thought was for this motherboard is in fact not... leaving me guessing at jumpers and such. I have scoured the internet high and low but I have not been able to find any further documentation.

2/ Having visually examined the motherboard exhaustively, I am able to connect everything except one critical thing - the case's front panel power switch! Without that, I am presuming the machine will not turn on. The "bench system" is powered by a free standing power supply with an external on/off switch, hence no issues up to now. So, I find myself with no way to get the machine to power up when I finish building it into the case.

So, no obvious way to signal the application of power and no documentation to help me resolve this. I am turning to the well skilled readers here at Vogons in hope of help.

I have attached a photo of the motherboard. Does anyone recognize it? It is labelled only "A340C-G" - no manufacturer name and no other lettering on the backside of the board. It is a 33 MHz / 40 MHz 386 DX motherboard.

Google searches for "A340C-G" turn up motherboards from two companies, Jetway and J-Bond, but NEITHER has a A340C-G; there is a G01 and a G02, both from J-Bond, but their documented layouts don't match the board I have. There is also one from Jetway, but it too does not match the board I have.

Does anyone recognize this mobo? Can you tell me who the manufacturer is, and even better, provide either a pointer to the documentation or a copy of it?
Am I overthinking this? Did 386-class machines simply power on when the power supply switch was turned on?

Thanks!

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  • A340C-G 386 Motherboard.jpg
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    A340C-G 386 Motherboard.jpg
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    A340C-G 386DX/33 Motherboard
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Reply 1 of 6, by PiotrUU

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The AT power supply (for this motherboard) has its own switch. The board does not control the power supply.

You turn off the computer when it is not doing anything (not writing anything to the hdd/fdd)

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  • off.jpg
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Last edited by PiotrUU on 2024-12-29, 22:26. Edited 1 time in total.

Reply 2 of 6, by analog_programmer

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No, I can't recognize this board, but fortunately TRW search sometimes does 😀 Your board looks like this one: https://theretroweb.com/motherboards/s/j-bond-a340c-g02

Last edited by analog_programmer on 2024-12-29, 22:07. Edited 1 time in total.

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Reply 3 of 6, by Horun

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What does the BIOS string say at boot up ? To me it looks like a variant of A340C-G02, nearly everything matches except the cache jumpers and those are silk screened....

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 4 of 6, by konc

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mac57mac57 wrote on 2024-12-29, 20:54:

2/ Having visually examined the motherboard exhaustively, I am able to connect everything except one critical thing - the case's front panel power switch!

This makes me think that you are trying to use an ATX case switch with your AT motherboard, as PiotrUU said earlier.

Reply 5 of 6, by mac57mac57

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Thanks all, yes I agree that the board looks most like a J-Bond A340C-G02, but that is not the label printed onto the board... and thanks for confirming that the machine should just turn on when I turn on the power supply.

... and yes indeed, the case is the wrong type for the motherboard. I bought the parts out of sequence, as they became available on eBay, which has caused some physical build issues in terms of physical fit and power supply connectors, but I *think* I have it all worked through. I should be able to finally be able to hit the "on" switch tomorrow or so. I'll report back the results here. Today, it is New Years Eve AND my wife's birthday - I don't think I will be getting much more retro-computing done except for this post! 😀

Thanks again!

Reply 6 of 6, by mac57mac57

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Quick closure here - the machine worked flawlessly when I hit the "on" button, so I managed to get all the jumpers, connectors and power correct. Nice machine now that it is running, and the 386DX/33 is a lot zippier than I had expected. It runs DOS like a speed demon and WFWG really well. I am very pleased with it.