386SX-40 Motherboard Not POSTing

Discussion about old PC hardware.

Re: 386SX-40 Motherboard Not POSTing

Postby appiah4 » 2019-7-01 @ 11:33

Murugan wrote:Hmmm same as mine except I have no speaker attached.


Oh please do break out the debug kit and check out your card because I have a feeling the issue may be identical :D
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Re: 386SX-40 Motherboard Not POSTing

Postby Murugan » 2019-7-01 @ 11:36

Hehe, I just moved into my new home and ATM everything is in boxes. I know where it is but I need to get settled first before I start with the hobby again. Give it a week or 2.

It's a different board than yours (Soyo 4SAW2) but the symptoms appear to be the same.
Last edited by Murugan on 2019-7-03 @ 13:28, edited 1 time in total.
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Re: 386SX-40 Motherboard Not POSTing

Postby appiah4 » 2019-7-01 @ 14:54

Murugan wrote:Hehe, I just moved into my new home and ATM everything is in boxes. I know where it is but I need to get settled first before I start with the hobby again. Give it a week or 2.

It's a different board than yours (Soyo 4SAW2) but the symptoms appear to be the samen.


I'm a patient man, I can wait. :cool:
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Re: 386SX-40 Motherboard Not POSTing

Postby Murugan » 2019-7-03 @ 13:28

I will report back ASAP.
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Re: 386SX-40 Motherboard Not POSTing

Postby Murugan » 2019-7-14 @ 09:09

Ok so I quickly set this board up. I get 4E 46 as a code.
Keyboard leds briefly light up when powered on but after that the keyboard error and no more led's.
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Re: 386SX-40 Motherboard Not POSTing

Postby appiah4 » 2019-7-18 @ 06:42

Murugan wrote:Ok so I quickly set this board up. I get 4E 46 as a code.
Keyboard leds briefly light up when powered on but after that the keyboard error and no more led's.


Same behavior (keyboard error after memory test complete), different debug code.. Is your BIOS AMI or Award?

I hope we can solve this issue with our boards. I'm guessing it might be a keyboard controller failure, is yours socketed? Mine is not, so it's not an easy replacement, maybe you could replace yours and try if it's socketed?
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Re: 386SX-40 Motherboard Not POSTing

Postby Murugan » 2019-7-18 @ 08:53

It's an Award BIOS.
My controller is not socketed sadly.
The board suffered from battery leakage and I couldn't get a signal from the Data pin or I did something wrong.

My codes are related to errors in the BIOS setup.
4E: If there is any error, show all the error messages on the screen & wait for user
to press<F1>.Manufacturing POST loop or display messages; Reboot if
manufacturing POST loop pin is set. Otherwise display any messages and enter
setup

46: display the setup message(to press Ctrl-Alt-Esc to enter setup), and enable
setup.
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Re: 386SX-40 Motherboard Not POSTing

Postby appiah4 » 2019-7-18 @ 09:18

Murugan wrote:It's an Award BIOS.
My controller is not socketed sadly.
The board suffered from battery leakage and I couldn't get a signal from the Data pin or I did something wrong.

My codes are related to errors in the BIOS setup.
4E: If there is any error, show all the error messages on the screen & wait for user
to press<F1>.Manufacturing POST loop or display messages; Reboot if
manufacturing POST loop pin is set. Otherwise display any messages and enter
setup

46: display the setup message(to press Ctrl-Alt-Esc to enter setup), and enable
setup.


The POST code says there was an error in an earlier stage and it stops POST there to report that, your board reports a keyboard error, same as mine.

Mine also had the battery leak, which I cleaned best I could. As far as I can see, mine has no connectivity issues with Data or Clock pins on the KBC. I THINK my issue is with 5V.. I will do more in depth testing tonight.

If you are certain that it's about Data, have you tried soldering a botch wire between Pin 2 of the keyboard connector and pin 39 of the KBC?

One thing that just occured to me, I know that the PINS of the keyboard connector have continuity to 5V, Data and Clock, but I don't know the CONNECTOR has it.. I never checked the connector side against the pins to verify, it may just be a broken connector for me. Wouldn't that be funny?
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i686:K6-2/400|128M|Rage|V2|CT4520/32M
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Re: 386SX-40 Motherboard Not POSTing

Postby Murugan » 2019-7-18 @ 09:38

I assume that I get the error because the BIOS is not set (CMOS mismatch). I haven't done anything to the board since I'm still in my learning fase with the multimeter. I don't even know where the 5v pin is on my board. I usually have the luck of having working equipment so I need to learn about repairing and diagnose :)
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Re: 386SX-40 Motherboard Not POSTing

Postby appiah4 » 2019-7-18 @ 21:33

OK, I need help from more electically educated people here.

I took a multimeter and tested every trace leading to and from the keyboard socket and everything checks out.

Moreover, here is what the circuit diagram appears to be:

OPTI 291WB Motherboard KB Circuit 01.JPG

This makes no sense to me. Why is the 5V pin also connected to the Data Pin on the KBC? Is this normal? I'm guessing there is something fundamentally wrong here, I don't understand whythe Data port would be connecte to +5V as well in parallel with the keyboard connector socket Pin 2 - R45 being connected to +5V makes no sense to my uneducated brain.

Can someone look at this and tell me what if anything may be wrong here?
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Re: 386SX-40 Motherboard Not POSTing

Postby gdjacobs » 2019-7-18 @ 23:44

It's a pull up arrangement. The data line from the keyboard only has to pull down to ground while avoiding an indeterminate state instead of pulling both ways.
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Re: 386SX-40 Motherboard Not POSTing

Postby appiah4 » 2019-7-19 @ 04:03

So it looks fine? Then I don’t know what else could possibly be wrong with this system if it does not boot when I replace the fuse other than a possibly faulty KBC.. The legs on it look dull so I’ll give it a spray of contact cleaner just in case but I guess adding a socket and replacing it is next..
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i686:K6-2/400|128M|Rage|V2|CT4520/32M
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Re: 386SX-40 Motherboard Not POSTing

Postby Tiido » 2019-7-19 @ 04:45

Problem is most probably some connection to a KBC if another KBC won't work in there. If you can borrow one from another board then do so, if it still gives the same error you got a broken trace or a via somewhere.
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Re: 386SX-40 Motherboard Not POSTing

Postby Murugan » 2019-7-19 @ 06:43

I will break out the board and multimeter again and see if I can educate myself and find all the pinouts. Frustrating being a noob...
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Re: 386SX-40 Motherboard Not POSTing

Postby appiah4 » 2019-7-19 @ 07:37

Tiido wrote:Problem is most probably some connection to a KBC if another KBC won't work in there. If you can borrow one from another board then do so, if it still gives the same error you got a broken trace or a via somewhere.


Pins 1-2-5 are definitely connected to the KBC, solid. If the circuit I posted above is also logical, then there should be no issue between the socket and the KBC. Aside from the blown fuse, which I shorted with a botch wire and that only served to blink the keyboard lights momentarily durin boot.

Say, tonight I will replace the blown fuse with these:

https://www.direnc.net/3a-250v-direnc-tip-sigorta

If that does not work, I will then remove the KBC and replace it with a DIP-40 socket, then install a KBC from one my 486 motherboards, such as this one:

Image

83C42 to replace 80C42 should probably work, it only seems to add PS/2 functionality etc.

And if that doesn't work, well I don't know which traces and vias to look at - any pointers about how the KBC and chipset/CPU are connected?
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Re: 386SX-40 Motherboard Not POSTing

Postby Tiido » 2019-7-19 @ 07:52

By connection to KBC I meant ISA or dedicated peripheral bus, not connection between keyboard and KBC. CPU is not able to talk to the KBC so either KBC is damaged or connection to it. There will be usual D0...D7, perhaps few address lines and read, write and enable strobe, plus clock signal.
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Re: 386SX-40 Motherboard Not POSTing

Postby appiah4 » 2019-7-19 @ 07:55

Tiido wrote:By connection to KBC I meant ISA or dedicated peripheral bus, not connection between keyboard and KBC. CPU is not able to talk to the KBC so either KBC is damaged or connection to it. There will be usual D0...D7, perhaps few address lines and read, write and enable strobe, plus clock signal.


Ok so I should basically check every single D and A pins and make sure they are connected to something without any continuity breaks. Understood. I'll get to it tonight, first replace the fuse (by the way, is the fuse I linked above OK? The fuse currently in place is transparent, the one I bought is ceramic, though I doubt it matters?) they check every single D and A leg extensively.
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i686:K6-2/400|128M|Rage|V2|CT4520/32M
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Re: 386SX-40 Motherboard Not POSTing

Postby Tiido » 2019-7-19 @ 08:53

That fuse will be just fine. As far as KBC connections go, they may not be directly connected to ISA but to smoe driver/buffer instead, some nearby 74x244 or 74x245 chip for example.
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Re: 386SX-40 Motherboard Not POSTing

Postby Murugan » 2019-7-19 @ 09:40

I checked too and I don't get a signal when probing pin 39 and pin 2 data so there is a broken trace but how to find it. I don't see anything going from pin 39...
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Re: 386SX-40 Motherboard Not POSTing

Postby Tiido » 2019-7-19 @ 10:15

Then there's a trace inside the board that reaches some via somewhere, and that via is where the problem is. I saw a lot of surpicious vias earlier. It is easy to connect top and bottom again but restoring connection to inner layer is difficult outside adding a patch wire to the destination.
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