Suntac 80286 Mainboards

Discussion about old PC hardware.

Re: Suntac 80286 Mainboards

Postby Deunan » 2019-4-08 @ 20:11

Well it's much easier if you have schematics. Plus we got lucky and all the "big" chips are still functioning properly.
Starting your electronics repair adventure with PC boards is probably not the best idea, but then again if you're willing to learn - why not. These 286 and even early 386 mobos and not yet that complicated.

You will need some tools though. Universal meter (preferably with fast beep on short) and I recommend a test card as well. With a test card you can select a mobo that's not completly dead, this raises the chances it can be repaired and it'll take less work in general.
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Re: Suntac 80286 Mainboards

Postby Montserrat » 2019-4-10 @ 18:04

wow, that was fast! another board saved from the trash! Congratultions predator99, and of course Deunan!
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Re: Suntac 80286 Mainboards

Postby Predator99 » 2019-4-26 @ 18:01

Predator99 wrote: 2019-1-26 @ 11:35
Did not manage to fix it so far...

But next one:
The attachment 286-Suntac-A2125580.jpg is no longer available


After some cleaning it looks better:
The attachment 286-Suntac-A2125580--cl.jpg is no longer available


Seems to be alive, but the delay line in the bottom left is loose, almost all pins broken. Need a replacement...

BIOS:
The attachment 286-Suntac-A2125580.rar is no longer available


I now replaced the damaged delay line with a socket and put a modified SN74LS14N on it.
viewtopic.php?f=46&t=66568&p=751131

With empty delay line socket the board is dead with display "--" on the POST card.

With the SN74LS14N it powers up. But there seems to be still a problem with the RAM. Supersoft dispays garbage CMOS data (not critical I think) and RAM failing bits 0,1,3,7. To my surprise I can exchange the RAMs in any way, its always the same scheme. I also removed all RAMs and still get the same result. The ICs are known working in the other Suntac-Board...

DSC_8497.JPG
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Re: Suntac 80286 Mainboards

Postby Deunan » 2019-4-26 @ 19:22

A problem with RAM that doesn't change when moving chips around would suggest the delay line substitution isn't working properly. I still think a HCT chip would do a better job than LS.
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Re: Suntac 80286 Mainboards

Postby Predator99 » 2019-4-26 @ 20:02

Yes, I am afraid thats a good explanation. I dont like to desolder a working delay line to verify. Therefore I will try with 74HCT14...
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Re: Suntac 80286 Mainboards

Postby Predator99 » 2019-5-01 @ 13:37

Hmm, did a better wiring job with the HCT but unfortunately still the same result...think I need to test with a known working delay line to be sure its the reason for the fault...
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IMG_9715r.jpg
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Re: Suntac 80286 Mainboards

Postby Deunan » 2019-5-01 @ 14:09

Please check which pins of the socket are actually connected to the chips. Original IBM 5150 has connections to: in, 20ns, 60ns and 100ns. 40 and 80 are unsused, and the delay line in general has different pinout.

Your replacement will only work on pins 12, 10 and 8, which correspond to 1, 3 and out on the original. 2 and 4 cannot be used as you have these signals inverted. HCT14 has propagation delay of about 20ns so you have 40ns, 80ns and 120ns taps. Maybe that's too slow but that depends on the actual delay line originally used (not all have 20ns per tap).

EDIT: According to Suntac schematics you need 30ns and 60ns delays, and that is pins 12 and 4 (and in on 1). Rewire your chip like this:
1 - in
2 -> 13
12 -> 11
10 -> 3

See if that works.
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Re: Suntac 80286 Mainboards

Postby Predator99 » 2019-5-01 @ 16:43

Yes, original is the ESAN 31A-5101. It has 100 ns total and 20 ns per TAP. Pinout is on the bottom right of the datasheet at the top the other thread:
viewtopic.php?f=46&t=66568&p=751131

Connected on the mainboard seem to be Pins
1, 4, 8, 12, 14

dl.jpg

(bottom view mirrored)

Will try the rewiring later....THANKS!
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Re: Suntac 80286 Mainboards

Postby Predator99 » 2019-5-01 @ 19:08

OK, almost there with wiring
1 - in
2 -> 13
12 -> 11
10 -> 3

Maybe it was just by chance as its not very reproducable. Did this with loose wires and will solder on the weekend.

But there seems to be another issue. Keyboard does not work and NumLock LED is very dark. At least one jumper needs to be set there, too. Maybe also some corrosion damage left, will check this after the memory being running reliable... UPDATE: Keyboard running, was not tight enough in the socket... :lol:


IMG_9720r.jpg

IMG_9724r.jpg
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Re: Suntac 80286 Mainboards

Postby Predator99 » 2019-5-03 @ 16:45

OK made a better soldering work on the 74LS14: This cabling works perfectly on every reboot!

Summarized:
- board appears to be totally dead with broken delay line
- 74LS14 is a good replacement but need to consider the required connectors on a case by case basis
- Deunan is the best, many thanks for helping me fixing my 2nd board!!!

stls14.jpg
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Re: Suntac 80286 Mainboards

Postby MMaximus » 2019-5-03 @ 21:46

So this means you fixed it? Congratulations guys! :cool:

In the mean time I've managed to get a working post card (ordered a cheap one from China but it didn't work so I got a slightly more expensive one from Europe on Ebay)

I'm trying to diagnose the problem on one of my Suntac boards with my very limited knowledge of electronics. It's this board:

Image

It's pictured here with no RAM, but I've tried with different combinations of RAM chips known to work in other boards and still no luck. I've also covered the BIOS chip with a sticker (believe it or not I didn't know about UV erasable chips when I took the photo), and replaced the BIOS chips with one from a working mobo so it's not this either.

The board powers up, but gives no display signal, nothing happens. The diag board doesn't give any diagnostic code either.

Image

Could it be the CPU? I would swap it to check but I don't have my PLCC extractor at hand at the moment.
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Re: Suntac 80286 Mainboards

Postby Deunan » 2019-5-03 @ 23:26

Connect reset switch. Does the RESET LED on the test card light up when you press it? Also, if you're using a modern 400W+ ATX PSU through an adapter, take note of this LED behaviour when you cut power to the PSU. There should be a brief moment when the LED lights up before the power runs out in the capacitors and the mobo goes dark.
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Re: Suntac 80286 Mainboards

Postby MMaximus » 2019-5-04 @ 21:39

I'm actually using an old AT PSU from a working system. I've used a nail to short the JP6 (reset) jumper on the board - and the LED on the test card lights up as long as I short this jumper. I assume it's a good sign? The "IRDY" LED on the test card stays off no matter what, but the other LEDs are on.

Also, I don't know what the JP2 jumper on the test card is for. The card came with some wire to connect this JP2 jumper somewhere. There's also a button on the test card which I don't know the use of. The user manual is in english but probably badly translated from Chinese like many products of this kind, and doesn't seem to make much sense. :confused:
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Re: Suntac 80286 Mainboards

Postby Deksor » 2019-5-04 @ 22:18

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)
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Re: Suntac 80286 Mainboards

Postby Deunan » 2019-5-04 @ 22:32

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.
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Re: Suntac 80286 Mainboards

Postby Deksor » 2019-5-04 @ 22:40

Mine is from 1989. I was really happy to discover that as this meant I didn't need to worry about corrosion :DI can dump my bios if needed, mine must be from the same manufacturer because it's nearly identical (I think I've spotted battery terminals on his, so that's not exactly the same, but other than this it's the same if I remember my board correctly).

Edit : here are some photos ! https://imgur.com/a/yqGc4zE

Sorry for view angle on some of them, I didn't want to bother it, it's been sleeping for few months and I wouldn't like to see it unhappy next time I power it on ^^
On image nº2 you can see the Dallas chip with the cr2032 mod behind the mfm cables
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Re: Suntac 80286 Mainboards

Postby Predator99 » 2019-5-05 @ 08:41

MMaximus wrote:
Also, I don't know what the JP2 jumper on the test card is for. The card came with some wire to connect this JP2 jumper somewhere. There's also a button on the test card which I don't know the use of. The user manual is in english but probably badly translated from Chinese like many products of this kind, and doesn't seem to make much sense. :confused:


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


Deksor wrote:Mine is from 1989. I was really happy to discover that as this meant I didn't need to worry about corrosion :DI can dump my bios if needed, mine must be from the same manufacturer because it's nearly identical (I think I've spotted battery terminals on his, so that's not exactly the same, but other than this it's the same if I remember my board correctly).

Edit : here are some photos ! https://imgur.com/a/yqGc4zE

Sorry for view angle on some of them, I didn't want to bother it, it's been sleeping for few months and I wouldn't like to see it unhappy next time I power it on ^^
On image nº2 you can see the Dallas chip with the cr2032 mod behind the mfm cables


Yes, can you dump your BIOS please? You can do that with NSSI without removing chips. Does it run with 16 MHz..?
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Re: Suntac 80286 Mainboards

Postby Deksor » 2019-5-05 @ 09:01

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.
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Re: Suntac 80286 Mainboards

Postby Predator99 » 2019-5-05 @ 09:45

Yes, crystal seems to be 24 MHz so CPU seems to be running at 12MHz. But its labeled as 8/10/12/16 so it might be possible to oberclock? Never tried...

For RAM upgrade I woiuld recommend a EMS/XMS card like this one ;-)
viewtopic.php?f=46&t=66089&p=747843
At least you can use the chaeper 41256 for further upgrade and dont need to buy 411000.

I upload you photo of your DATAMINI board gain, dont think imgur is reliable for the future...
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Re: Suntac 80286 Mainboards

Postby Deksor » 2019-5-05 @ 11:14

Yeah I know EMS/XMS cards, but I'd rather have that onboard (and the ones I can find are about the same price as the chips I need anyways :lol:)

DATAMINI is the brand of the computer, but I think this is a rebranded motherboard of some kind. I can even bring the BIOS setup disk image :)

As for the bios itself, I can simply dump it using my TL866 :D
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