Old KEnitec 286 Plus (suntac) Rescue, will need help.

Discussion about old PC hardware.

Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Montserrat » 2019-3-16 @ 12:40

Was about to do tthat haha you saved me so much time looking at schematics :D
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Montserrat » 2019-3-16 @ 17:39

Ok, repaired all damage, and a new socket is in place, i have tested all 20 pins from '245 and now they are all conected to destination, ALL OK NOW.

Powered on the board and got same results as usual.

So now im trying to test the '245 in the breadboard, but have some problems, to the prove 5v dont go througth 100 ohm resistor, so pin 20 is not getting power.
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Deunan » 2019-3-16 @ 18:02

Ok, connect it directly to 5V then. I guess the internal power draw of ALS series is just too big and any lower than 100 ohm doesn't really protect the ports anyway.
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Montserrat » 2019-3-16 @ 18:19

The test sequence (with a probe): connect pin 19 to pin 20 (so it's at 5V through resistor) and probe pins 2-9 and 11-18. You should not get any LED brightly lit.
Then connect pin 19 to ground and pin 1 to pin 20. Now probe pins 11-18, one by one, like this:

- connect pin 9 to ground through 1k resistor
- probe pin 11, it should indicate low level
- reconnect pin 9 to +5V through 1k resistor
- probe pin 11 again, it should indicate high level

Do the same for pin pairs: 9->11, 8->12, 7->13, 6->14, 5->15, 4->16, 3->17, 2->18

If all is good, reconnect pin 1 to ground. Repeat the test but reverse the input/output pin of each pair.


Done, all is good exect for pair 9 > 11, wich is giving low (low means green/ground right?) on both 5v and gnd test. The other pairs are ok.

PD: ah forgot to comment that again '245 pin 19 is not connected to 002 pin 45 but 46 one, just for it has any relevance.
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Deunan » 2019-3-16 @ 19:52

Low or high on the probe depends on how you connected the LEDs (is which direction). If in doubt just touch ground with the probe tip and the LED that is now lit is for low, then touch +5V and that LED is for high.

9->11 is wrong then? And what about 11->9? This is bit D7 and you did measure a different behaviour on it while testing the 8042 but I thought it might be due to broken connection.

If you confirm it's toast then try this:
1) bend the pin 9 and 11 so they don't come into contact with the socket
2) solder a 100 ohm resistor on the bottom of the mobo between pins 9 and 11
3) put the chip (with the pins bent) into the socket
4) remove any ISA cards, except the test card (any video cards as well)
5) power up and see what test code you get now

With ISA card removed there shouldn't be any bus conflicts but just in case don't keep the system powered like this for a long time. Just long enough for code tests.
It might be difficult to buy ALS245 but I think it should work well if you substitute it with ACT245. HCT245 might be too slow and AC245 is not fully TTL-compatible so avoid those, unless you only want to test.
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Montserrat » 2019-3-16 @ 20:39

Well got new codes! i bended the pins and soldered the 100 ohms resistor, got new codes and beepcode:

Image

Its a 2-1-3 beep code(from reference):

2-1-3 -> 64KB RAM failure Bit 2; This data bit on the first RAM IC has failed. Replace the IC if possible

and the post card shows:

01
02
03
04
05
06
08
09
12 -> Bit 2 first 64K RAM failure)

I supose i need to replace that '245?

Mouser has distribution center near my home, DM74ALS245AN is the original his website propose SN74ALS245AN as substitute:

https://www.mouser.es/ProductDetail/?qs ... pwVg%3D%3D
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Deunan » 2019-3-16 @ 21:34

Yeah, it has to be replaced (and the resistor removed of course). If you're buying from Mouser anyway then get a few just in case. Also maybe get one 74ACT245 as well since it should use less power and not heat up so much.

I will try to look for this new error in the BIOS code when I have some time, but for now remove all the RAM chips from sockets and inspect - sometimes oxidation will prevent proper socket contact. Even just re-seating them might work. If not, swap them around a bit, see if the code changes, you'll know if it's really the chip or rather the connection/socket that's bad.
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Montserrat » 2019-3-17 @ 10:32

Image

Image

YAY!! Today i have not very much time for more testing, but now its alive hehehe. More soon.
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Montserrat » 2019-3-17 @ 11:09

Aaaaand its gone.

Now i get a diferent error every time i try to boot. :S.
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Predator99 » 2019-3-17 @ 11:11

WOW incredible...! Congratulations to both of you...!

I am sure you will get this reproduced.

Would be happy to read a summary what parts had to be fixed at the end...?
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Deunan » 2019-3-17 @ 12:37

Montserrat wrote:Now i get a diferent error every time i try to boot. :S.


What codes do you get? Did you replace the 245 already?
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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Postby Montserrat » 2019-3-17 @ 21:24

I've extracted and put back again all memory modules, cleaning sockets and pins, memory test was 640k + 1400k, so all memory its in good condition.

I think diferent codes are due to fried 245, so i better do not power up the mobo again until i replace that, just for safety. The codes i remember were:

21 Master DMA register failure
27 Keyboard controller test failure
34 No time tick

Too much randomness...now i need to find a new '245.
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