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Suntac 80286 Mainboards

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Reply 80 of 150, by MMaximus

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Deunan wrote:
I asked about ATX power supply beacuse pretty much all decent ones are 450W+ so the effect with the LED is easy to spot. But you […]
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I asked about ATX power supply beacuse pretty much all decent ones are 450W+ so the effect with the LED is easy to spot. But you can try that with AT PSU as well, though the results might not be conclusive. The reset switch works as it should on your mobo and so the problem doesn't seem to be reset related.

BTW the JP2 and cable for the test card are to connect the buzzer on it in place of PC speaker. You can verify that by testing connection between those two on the card. No idea what the button is for, I've never used it.

Well it could be the BIOS got corrupted. Not by UV light, unless you kept the board out in the direct sun without the EPROM windows covered. Fluorescent light doesn't really erase these unless it's years of exposure. Or lamps used to kill germs. EPROMs sometimes just flip back to "1" - it's a natural process that takes years even for weak cells but it happens. The mobo should output some error codes even without RAM, so long the CPU works and the chipset is not completly dead.

Do you have something to dump the EPROMs? Or maybe another board to try swapping both?

This mobo uses Motorola RTC, MC14618A - a very common chip. I'm actually surprised there were any Suntac 286 with Dallas chips. Must've been pretty late models.

Thanks for all this useful info. I swapped the EPROMs with ones from a working board and the board still doesn't work - whereas the working board works with the EPROMs from the defective board so we can probably rule this out. I'm waiting for a cheap PLCC extractor I've ordered to arrive and then I'll swap CPUs and see if it's the problem.

Deksor wrote:

Hey I think I have this exact same board in my 286 !

What's odd though is that I can't see any RTC on your board ...

Mine uses a DALLAS rtc chip, but I don't see it on yours either it's actually not the same board, or they used a different way, or it's missing on yours (I haven't opened my 286 since some time now so I don't exactly know where it is, I'll try to check that a bit later)

They look very similar but my boards had barrel batteries that I've removed. I'm now using external battery packs, it works really well.

I had 5 identical boards in total: I put one in a system that I sold, gave one of the non-working ones to Predator99, and now I have 2 functional boards and 1 defective left. I'll see what I can do with the non-working one but if I can't repair it I'll gladly give it away to someone who would want to have a go at it. 😎

Predator99 wrote:

Yes, jumper is for speaker connection. Button is for switching back to the previous code displayed.

Thanks for the info!

Predator99 wrote:

Yes, can you dump your BIOS please? You can do that with NSSI without removing chips. Does it run with 16 MHz..?

I'd be interested to see if the BIOS from Deksor's board is a different one: the one on mine and Predator's is Phoenix 3.10.22. Deksor, does your BIOS offer you the option of user-type HDD?

Actually I was thinking the same thing about 16Mhz... would our boards work at 16Mhz if we swapped the CPU and the crystal? Predator let me know if you try this 😀

Deksor wrote:

No the CPU is 12MHz on mine. Actually I wish I had ram chips to upgrade to 4MB, but I'm stuck to 1MB unless I pay 60€ of ram chips.

I didn't know 411000s were so expensive! 😲 All the boards I had came each with one bank of 411000s to give 2M RAM, so with both banks full it gives a total of 4M.

Reply 81 of 150, by Deksor

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BIOS dumped ! (I don't know which one is the high chip and which one is the low chip, so I took note of what sticker is on it compared to the photo.)

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Type 47 is just another preset drive unfortunately.

Also, I've discovered something else. I had an intuition of something, so I removed the controller card just to look underneath the mfm/floppy cables, and guess what I've seen ? Unpopulated battery spot ! So now I'm almost 100% MMaxmimus has the same board as me, just that instead of the MC146818AP chip, there's a DALLAS battery RTC chip.

I've also the manuals of that computer, and the motherboard is documented, so I might scan that someday.

Reply 82 of 150, by Predator99

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Thanks for uploading, works!
Is there any way to get into the Setup..? Didnt find the correct key? Or only provided on floppy?

IMG_4638r.jpg
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Reply 85 of 150, by Predator99

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As in the latest board the keyboard BIOS was damaged by corrosion (top on picture) I tested some other replacements I had in spare. I think they are from 286-486 class PCs. Also took one from anoher 386 board, not on picture.

All work without problem. They seem to be interchangable between CPU classes and BIOS manufacturers.

Without Keyboard BIOS post card stops at "02 01".

keyboard bios.jpg
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Reply 86 of 150, by Deunan

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So guys, I saw one of these Suntac mobos for sale for some 40EUR shipping included and decided to buy it. Seller said it doesn't boot but beeps if there is no video card. I pulled the trigger mostly because the photos showed no battery corrosion, even though the NiCd barrel is still there. There is none exactly like it in this thread so far but this one is almost a match: Suntac 80286 Mainboards

I'll dump the BIOS later today and make some photos soon but first I had to give the PCB a bath - whoever used it before me was a smoker and I don't deal well with that. So I won't be powering it up until I'm sure it's fully dry. I might even remove the battery first, we'll see. I hope can get it running, it really looks pretty decent, I've managed to repair worse.

I do have a question though, I've removed the CPU (I like this fancy socket) and it's AMD branded R80286-10/S. Date code is 1989 week 9. So it's a 10MHz CPU but the main crystal is 24MHz so it should be running at 12MHz. Weird, did someone replace the CPU or was this a "factory overclock" - what do you think? What are the chances of getting a 10MHz 287 to work properly on 12MHz, since the CPU is already over spec I might go for a cheaper coprocessor as well.

Also, the close but not quite exact Suntac I've linked above has X1 at 27.125MHz - was that original crystal as well? Or another attempt at overclocking a 12MHz CPU this time?

Reply 87 of 150, by Predator99

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Hi Deunan, happy that you also like these boards and bought one 😉 You should have told me, I have at least one in spare that is not running smoothly and would have been happy to give it to you. Who if not you would be able to repair it? 😎 😎 😎

As far as I know all of these boards I own are running at 12 Mhz and many of them have only a 10 MHz CPU installed. Think this was quite common. At least I didnt modify anything on the boards you can see on the photos I posted here.

Regarding the X1 on the board linked by you: Good question, also because the crystal is labeled "25M / 20M" on the pcb and 27.125MHz is installed. Maybe I should measure the speed it is running at...

Reply 88 of 150, by Deunan

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Here's the BIOS, both EPROMs and a combined version for emulators and whatnot.

Suntac AMI 286 BIOS.jpg
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Reply 89 of 150, by Predator99

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I already can confim your ROMs are OK, thanks!

And: Your combined image is the 1st one that runs in PCem...! "AMI 286 clone" accepts it. I tried most of my images but none worked. Maybe I made a mistake whith combining the odd/even? Strange, will verify this.

But screenshots are from real hardware:

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Reply 90 of 150, by Deunan

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Can you test something for me? With this BIOS installed, remove the 8042 keyboard controller and boot the system, with test card in ISA slot. What code it stops at and do you get any beeps?

Reply 91 of 150, by Predator99

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Deunan wrote:

Can you test something for me? With this BIOS installed, remove the 8042 keyboard controller and boot the system, with test card in ISA slot. What code it stops at and do you get any beeps?

Sure. Thats interesting. After removing the 8042 the system came up with your BIOS.

A message is displayed on the VGA:
8042 GATE-A20 ERROR
SYSTEM HALTED

POST sequence is:
31
30
25
24
23
22
21
20
1a
19
18
17
16
15
12
11
10
0b
0a
09
08
07
06
04
14
03

Reply 93 of 150, by Deunan

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Welp. Mine dies at 25->30, that's the last code I see. CPU is still running but that's it. I also get 2 short and 8 long beeps on code 19->1a and get no VGA ouput at all. Doesn't seem like the color/mono jumper does anything but it's connected to the 8042. Although I can't be sure what is short or long beep as it uses different pitch, so maybe it's supposesed to be something else. Can't turn on CAPS on keyboard at any time either.

This is very weird and I sort of suspect the CPU since I can see activity on all ISA address, data and control lines. But it could be another cracked solder joint on the big chips, already fixed one of those and now the systems no longer acts randomly on boot. I sure hope it's not a weird failure of the 8042, I can't easily replace that. But it does seem to generate IRQ1...

Reply 94 of 150, by Predator99

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Deunan wrote:

Welp. Mine dies at 25->30, that's the last code I see. CPU is still running but that's it. I also get 2 short and 8 long beeps on code 19->1a and get no VGA ouput at all. Doesn't seem like the color/mono jumper does anything but it's connected to the 8042. Although I can't be sure what is short or long beep as it uses different pitch, so maybe it's supposesed to be something else. Can't turn on CAPS on keyboard at any time either.

This is very weird and I sort of suspect the CPU since I can see activity on all ISA address, data and control lines. But it could be another cracked solder joint on the big chips, already fixed one of those and now the systems no longer acts randomly on boot. I sure hope it's not a weird failure of the 8042, I can't easily replace that. But it does seem to generate IRQ1...

As far as I can see 30 is related to the Video? What sequence do you get without VGA? Tried another one or a CGA?
http://www.elstonsystems.com/dl/manual_postcard_32.pdf

With my board there is a continous beeping at the 31, nothing before.

Reply 95 of 150, by Deunan

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Those early AMI BIOSes have different codes than later ones. So I'm not sure what 30 means, according to this page it's related to CPU protected mode test: http://www.bioscentral.com/postcodes/amibios.htm
And that actually checks out with 31 being the failure code once you remove 8042 - the A20 gate control is lost so PMODE test fails. But then again that page doesn't list code 25 and yours does.

It could be that this mobo doesn't like my Trident 8900D, but the only other ISA video card I have is a Realtek VGA. Don't have it here, forgot to bring it, will test tomorrow. I don't have any mono (MDA/Hercules) or CGA cards, and no monitors that would take such signal anyway. Unless I can hack together some resistor "DAC" for OSSC and try that way. Basically with or without the VGA I get the 2-8 beeps.

So, one more test, can you see what it does without graphics card on this BIOS?

Reply 96 of 150, by Predator99

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OK last one for today:
With keyboard BIOS and without VGA:
30
24
23
22
21
20
1e
1d
1a
19
17
16
15
12
11
10
0c
0b
0a
09
08
07
06
14
03
02
01

Without Keyboard BIOS and without VGA
31
30
25
24
23
22
21
20
1e
1d
1a
19
18
17
16
15
12
11
10
0b
0a
09
08
07
06
04
14
03

But I have to adit without these components my board does not seem to be stable and it starts only every 2nd attempt....

Reply 98 of 150, by Predator99

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I have tried many different VGA and found only few incompatibles. Currently I have ET4000 and TVGA9000. Try to switch all jumpers on your VGA even if you dont know what they're for. Will add beep codes later here.

Reply 99 of 150, by Deunan

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I've spent a few hours trying to gather some info on VGA cards in older systems and was rewarded with this: http://www.vcfed.org/forum/showthread.php?392 … 4322#post484322

So it would seem older systems that use DMA-like RAM refresh method tend to generate spurious ALE pulses during refresh cycles. That in turn causes some ISA cards to latch a wrong address if the refresh happens during a read/write cycle. The "workaround" is to use cards that don't rely on ALE - some Tridents do, some don't, it's best to actually inspect the ISA edge connector and see if the signal is routed anywhere (usually, to lower hard gold usage, the contact will be missing completly).

Not sure if that is applicable to Suntac boards, or is it going to help my case (yet), but the Realtek doesn't have ALE connection and my Trident 8900D does. I will test later today but this piece of information might be of some use to others so I'm posting it here.

UPDATE: The good-for-nothing Realtek 3105 doesn't work either. But, there is a difference. With the Realtek VGA plugged in and the keyboard controller removed, I get up to code 3A, which should be RAM test. When I remove the card I get 1A error with beeps again. So it would seem the card is being detected now, but possibly as mono. I still have no idea why none of this works with 8042 in the board and the jumpers set to color or mono. I'm going to try a different BIOS to see if it's a card detection issue or an actual mobo problem.