rasz_pl wrote on 2022-07-08, 18:06:

did you mean 1 long 2 short? […]
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butjer1010 wrote on 2022-07-08, 13:53:

without VGA board also beeps, but 1 long and 4 short beeps

did you mean 1 long 2 short?

butjer1010 wrote on 2022-07-08, 13:53:

I tried put the vga in 8-bit slot, same result, same picture on monitor.

🙁 such a nice and convenient theory disproved

butjer1010 wrote on 2022-07-08, 13:53:

I get 3 leds flash on keyboard when i turn on the computer, but nothing happens when i press any of "locks" when garbled screen shows up.

means bios crashes/gets stuck

post codes and order of initialization: http://mrbios.com/techsupport/award/postcodes.htm [AMI New BIOS; 06/06/92-08/08/93]
must be hanging somewhere between 2C and 2D? hmm how is the 5V on ISA slot? lack of proper power would make VGA draw parasitic power thru data pins and act weird

What happens when you do a hardware reset using S1 reset jumper?

Off the wall idea - try taking off JP2 jumper switching to mono monitor, with any luck this will force text mode 7 with different base address and attribute meaning, and produce different picture

poke carefully at all the 82C495XLC chipset pins with a toothpick to check if there arent any loose

Im running out of ideas, deeper diagnosing would require some tools (any of: post card, eprom flasher, logic analyser)

PS diagram of reverse engineered board on this chipset https://alexandrugroza.ro/microelectronics/sy … c-schematic.png sadly modular and not pdf , but still great resource. You can see where all the 244/245 buffers required for proper ISA operation connect

did you mean 1 long 2 short?
-actually, 2 very short beeps, and after one second 8 short beeps more???

What happens when you do a hardware reset using S1 reset jumper?
-PC restarts 😀, and broken screen again 😀

try taking off JP2 jumper switching to mono monitor, with any luck this will force text mode 7 with different base address and attribute meaning, and produce different picture
-same result without JP2 jumper

poke carefully at all the 82C495XLC chipset pins with a toothpick to check if there arent any loose
-today i tried to "fix" possible cold solder joints with flux and hot air, nothing has changed. I could try with toothpick, but i'm pretty sure that if there was any bad solder joints before, now i have fixed them.

hmm how is the 5V on ISA slot? lack of proper power would make VGA draw parasitic power thru data pins and act weird
-can You please spare me a time and tell which pins will give me possible 5V on ISA? Thanks in advance.

PS diagram of reverse engineered board on this chipset https://alexandrugroza.ro/microelectronics/sy … c-schematic.png sadly modular and not pdf , but still great resource. You can see where all the 244/245 buffers required for proper ISA operation connect
- i'm lost when i see this picture 😀 I'm not that good to understand all of this, i'm regular, maybe a little advanced user, but not a master like You 😀

butjer1010 wrote on 2022-07-08, 21:31:

butjer1010 wrote on 2022-07-08, 21:31:

-actually, 2 very short beeps, and after one second 8 short beeps more???

https://www.lifewire.com/amibios-beep-codes-2624543
"Two short beeps mean there has been a parity error in base memory. This problem affects the first 64 KB block of memory in your RAM."
http://www.bioscentral.com/beepcodes/amibeep.htm
"2 short Memory parity error A memory parity error has occurred in the first 64K of RAM. The RAM IC is probably bad"

hmm, why would it pass with VGA but beep RAM error without it? something floating without a card?

butjer1010 wrote on 2022-07-08, 21:31:

-PC restarts 😀, and broken screen again 😀

just to be sure exact same broken screen? and does keyboard blink 3 LEDs when you restart with jumper?

butjer1010 wrote on 2022-07-08, 21:31:

-same result without JP2 jumper

exact same broken screen with one odd green character?
were other VGA cards you tried all the same model? did they all produce exact same picture? or just one looking similar?

butjer1010 wrote on 2022-07-08, 21:31:

-today i tried to "fix" possible cold solder joints with flux and hot air, nothing has changed. I could try with toothpick, but i'm pretty sure that if there was any bad solder joints before, now i have fixed them.

cant be sure without poking at pins. I solder crap for 2030(Ffffff) years and I still test my work 😀

butjer1010 wrote on 2022-07-08, 21:31:

hmm how is the 5V on ISA slot? lack of proper power would make VGA draw parasitic power thru data pins and act weird
-can You please spare me a time and tell which pins will give me possible 5V on ISA? Thanks in advance.

https://upload.wikimedia.org/wikipedia/common … SA_Bus_pins.svg

butjer1010 wrote on 2022-07-08, 21:31:

PS diagram of reverse engineered board on this chipset https://alexandrugroza.ro/microelectronics/sy … c-schematic.png sadly modular and not pdf , but still great resource. You can see where all the 244/245 buffers required for proper ISA operation connect
- i'm lost when i see this picture 😀 I'm not that good to understand all of this, i'm regular, maybe a little advanced user, but not a master like You 😀

Im also lost when I look at this diagram 😀, thats why I said its not the best. You have to manually read labels and look for corresponding labels to connect the dots 🙁
For example look at the box in the center called "address data bus transceivers something something". Those are the 7x 245 and 1x 244 chips located between ISA slots on your board.

But now with that beep code clarification I would start by
-locating 4 tested 30 pin SIMMs.
-taking off all socketed chips near original damage and going over all the traces between RAM - CACHE - Chipset. There is most likely a via or trace broken there.

rasz_pl wrote on 2022-07-08, 22:24:

https://www.lifewire.com/amibios-beep-codes-2624543 "Two short beeps mean there has been a parity error in base memory. This pro […]
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butjer1010 wrote on 2022-07-08, 21:31:

butjer1010 wrote on 2022-07-08, 21:31:

-actually, 2 very short beeps, and after one second 8 short beeps more???

https://www.lifewire.com/amibios-beep-codes-2624543
"Two short beeps mean there has been a parity error in base memory. This problem affects the first 64 KB block of memory in your RAM."
http://www.bioscentral.com/beepcodes/amibeep.htm
"2 short Memory parity error A memory parity error has occurred in the first 64K of RAM. The RAM IC is probably bad"

hmm, why would it pass with VGA but beep RAM error without it? something floating without a card?

butjer1010 wrote on 2022-07-08, 21:31:

-PC restarts 😀, and broken screen again 😀

just to be sure exact same broken screen? and does keyboard blink 3 LEDs when you restart with jumper?

butjer1010 wrote on 2022-07-08, 21:31:

-same result without JP2 jumper

exact same broken screen with one odd green character?
were other VGA cards you tried all the same model? did they all produce exact same picture? or just one looking similar?

butjer1010 wrote on 2022-07-08, 21:31:

-today i tried to "fix" possible cold solder joints with flux and hot air, nothing has changed. I could try with toothpick, but i'm pretty sure that if there was any bad solder joints before, now i have fixed them.

cant be sure without poking at pins. I solder crap for 2030(Ffffff) years and I still test my work 😀

butjer1010 wrote on 2022-07-08, 21:31:

hmm how is the 5V on ISA slot? lack of proper power would make VGA draw parasitic power thru data pins and act weird
-can You please spare me a time and tell which pins will give me possible 5V on ISA? Thanks in advance.

https://upload.wikimedia.org/wikipedia/common … SA_Bus_pins.svg

butjer1010 wrote on 2022-07-08, 21:31:

PS diagram of reverse engineered board on this chipset https://alexandrugroza.ro/microelectronics/sy … c-schematic.png sadly modular and not pdf , but still great resource. You can see where all the 244/245 buffers required for proper ISA operation connect
- i'm lost when i see this picture 😀 I'm not that good to understand all of this, i'm regular, maybe a little advanced user, but not a master like You 😀

Im also lost when I look at this diagram 😀, thats why I said its not the best. You have to manually read labels and look for corresponding labels to connect the dots 🙁
For example look at the box in the center called "address data bus transceivers something something". Those are the 7x 245 and 1x 244 chips located between ISA slots on your board.

But now with that beep code clarification I would start by
-locating 4 tested 30 pin SIMMs.
-taking off all socketed chips near original damage and going over all the traces between RAM - CACHE - Chipset. There is most likely a via or trace broken there.

just to be sure exact same broken screen? and does keyboard blink 3 LEDs when you restart with jumper?
-Yes, exact same broken screen, and keyboard doesn't blink after restart.

hmm how is the 5V on ISA slot? lack of proper power would make VGA draw parasitic power thru data pins and act weird
-That's when things became interesting! PIN 03- 4,99V, pin 05- -3,5V???, pin 29 - 2,55V??? Pins 07 and 09 are 11,88 and -11,88V.

But now with that beep code clarification I would start by
locating 4 tested 30 pin SIMMs.
-Tried with more than 20 RAMs, all working on other MBOs.

taking off all socketed chips near original damage and going over all the traces between RAM - CACHE - Chipset. There is most likely a via or trace broken there.
So, again 🙁

The RAM IC is probably bad
Maybe if i can find same IC on other boards and change the IC, Can this be a "winner"? This is the "upper" chip i mark it in my pictures?

I think i screwed up MBO for good now. When i measured voltages (again) on isa slot, i think i shorted 4th and 5th pin with probe, and now the board is completely dead!!! There was no smoke, nothing, but i suspect i did this, because before measuring everything was "working". I will try tomorrow morning again, it's almost 2 am here, maybe tomorrow i will have more luck. 🙁 🙁 🙁

butjer1010 wrote on 2022-07-08, 23:37:

-Yes, exact same broken screen, and keyboard doesn't blink after restart.

ok, so the keyboard is not being initialized, means bios crashes Very early on and what we see on screen must be default uninitialized VGA garbage

butjer1010 wrote on 2022-07-08, 23:37:

-That's when things became interesting! PIN 03- 4,99V, pin 05- -3,5V???, pin 29 - 2,55V??? Pins 07 and 09 are 11,88 and -11,88V.

-3.5V is "fine" as nothing usually uses negative voltage
2.5V is deffo not fine, coincidentally its also what you would get while measuring B30 OSC - a one pin over 😀
there is one more pin on the 16bit part of the slot with +5V, D16

butjer1010 wrote on 2022-07-08, 23:37:

The RAM IC is probably bad
Maybe if i can find same IC on other boards and change the IC, Can this be a "winner"? This is the "upper" chip i mark it in my pictures?

no, they mean simm ram, as in BIOS failed while verifying ram aka there is problem with accessing main ram
damage might creped under one of the SIMM slots and wont be visible, can only be found by
- desoldering simm slots, tedious and very difficult
- measuring between pins od SIMM sockets and pins of the chipset while looking at simm socket pinout and chipset datasheet

butjer1010 wrote on 2022-07-08, 23:43:

I think i screwed up MBO for good now. When i measured voltages (again) on isa slot, i think i shorted 4th and 5th pin with probe, and now the board is completely dead!!! There was no smoke, nothing, but i suspect i did this, because before measuring everything was "working". I will try tomorrow morning again, it's almost 2 am here, maybe tomorrow i will have more luck. 🙁 🙁 🙁

yep, -5V (or even -3V) will kill buffers. You fried 82C206. Pin B4 or B6 is now most likely permanently grounded shorting this chip.

rasz_pl wrote on 2022-07-09, 02:14:

ok, so the keyboard is not being initialized, means bios crashes Very early on and what we see on screen must be default uniniti […]
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butjer1010 wrote on 2022-07-08, 23:37:

-Yes, exact same broken screen, and keyboard doesn't blink after restart.

ok, so the keyboard is not being initialized, means bios crashes Very early on and what we see on screen must be default uninitialized VGA garbage

butjer1010 wrote on 2022-07-08, 23:37:

-That's when things became interesting! PIN 03- 4,99V, pin 05- -3,5V???, pin 29 - 2,55V??? Pins 07 and 09 are 11,88 and -11,88V.

-3.5V is "fine" as nothing usually uses negative voltage
2.5V is deffo not fine, coincidentally its also what you would get while measuring B30 OSC - a one pin over 😀
there is one more pin on the 16bit part of the slot with +5V, D16

butjer1010 wrote on 2022-07-08, 23:37:

The RAM IC is probably bad
Maybe if i can find same IC on other boards and change the IC, Can this be a "winner"? This is the "upper" chip i mark it in my pictures?

no, they mean simm ram, as in BIOS failed while verifying ram aka there is problem with accessing main ram
damage might creped under one of the SIMM slots and wont be visible, can only be found by
- desoldering simm slots, tedious and very difficult
- measuring between pins od SIMM sockets and pins of the chipset while looking at simm socket pinout and chipset datasheet

butjer1010 wrote on 2022-07-08, 23:43:

I think i screwed up MBO for good now. When i measured voltages (again) on isa slot, i think i shorted 4th and 5th pin with probe, and now the board is completely dead!!! There was no smoke, nothing, but i suspect i did this, because before measuring everything was "working". I will try tomorrow morning again, it's almost 2 am here, maybe tomorrow i will have more luck. 🙁 🙁 🙁

yep, -5V (or even -3V) will kill buffers. You fried 82C206. Pin B4 or B6 is now most likely permanently grounded shorting this chip.

You fried 82C206
SIS chip on this board? So, if i find same chip and replace it, this could help, or did i permanently fried this board? 🙁 I found on my few dead 386 boards opti 82c206 chip, but will it work instead SIS chip, are they pin to pin compatible?

afaik they are unified, universal and exchangeable between all taiwan contemporary manufacturers
First check if its really dead, does it get hot? is there a dead short on 5V rail? does the PSU cut off voltages on start? what is the resistance of B4/B6 ISA pins and overall 206 pins to ground and 5V rails (resistance always measured on powered off system).
removing 206 will put you back where you started - bios still able to start executing, but quickly failing at 0E where it tries to test CMOS (CMOS is in 206 chip) or failing even earlier like before because there is bad memory connection on the board

rasz_pl wrote on 2022-07-09, 11:25:

afaik they are unified, universal and exchangeable between all taiwan contemporary manufacturers
First check if its really dead, does it get hot? is there a dead short on 5V rail? does the PSU cut off voltages on start? what is the resistance of B4/B6 ISA pins and overall 206 pins to ground and 5V rails (resistance always measured on powered off system).
removing 206 will put you back where you started - bios still able to start executing, but quickly failing at 0E where it tries to test CMOS (CMOS is in 206 chip) or failing even earlier like before because there is bad memory connection on the board

It is not hot, it is cold after 3 minutes?!?
How can i check is there a dead short on 5V rail? You meant on PSU connector or on SIS chip?
between B4/B6 on ISA - 3.88kOhm
Weird thing is when i measure 5V on isa B1 and B29 pin, now it is normal 5V, and before i made a mess, there was 2.55V???
Do You have schematics of 206 chip, so i can see 5V rails on chip?
If i manage to solve this 206 chip problem, i will desolder ram slots to see if there is some broken trace.
100 times thanks man, You've been very helpfull, sorry if i have took Your time.

butjer1010 wrote on 2022-07-09, 12:01:

It is not hot, it is cold after 3 minutes?!?
How can i check is there a dead short on 5V rail? You meant on PSU connector or on SIS chip?

short on power rail would mean no 5V, if you measure 5V there is no short on power

butjer1010 wrote on 2022-07-09, 12:01:

between B4/B6 on ISA - 3.88kOhm

between ground and B4 is 3Kohm, and B6 and ground same?

butjer1010 wrote on 2022-07-09, 12:01:

Weird thing is when i measure 5V on isa B1 and B29 pin, now it is normal - 5V, and before i made a mess, there was 2.55V???

most likely explanation: because yesterday you measured B30 by accident instead of B29, its a clock signal oscillating between ground and 5V therefore might show as 2.5V on the meter. Its even possible you shorted B30 to B29 blowing the oscillator

butjer1010 wrote on 2022-07-09, 12:01:

Do You have schematics of 206 chip, so i can see 5V rails on chip?

I see SIS calls this 85C206 and not standard 82c206
http://www.bitsavers.org/components/opti/dataSheets/
Page 6 http://www.bitsavers.org/components/opti/data … ller_199608.pdf
you will have to sanity check if its the same pinout. Easiest is looking at VCC and GND pins and checking if they are wired to ground/power as in the datasheet, then moving to IRQ pins and corresponding ISA signals etc

butjer1010 wrote on 2022-07-09, 12:01:

If i manage to solve this 206 chip problem, i will desolder ram slots to see if there is some broken trace.

two options
1 difficult and prone to failure (melted sockets, ripped traces): desoldering
2 imo easier: going pin by pin with documentation and checking continuity while making notes. this means you will have to force yourself to understand https://alexandrugroza.ro/microelectronics/sy … c-schematic.png 😀

butjer1010 wrote on 2022-07-09, 12:01:

100 times thanks man, You've been very helpfull, sorry if i have took Your time.

helping people fix old gear is fun
if you really want to fix this particular board, and I would understand giving up 😀, you will need a $5-10 ISA POST card at the very least. $10 "USB Logic Analyzer 24MHz 8 Channel" wouldnt hurt either, but $50 16 channel is preferable. It quickly starts to add up and becomes uneconomical for a one off deal, doesnt make sense if its not your hobby. That or access to hackerspace with proper gear.

rasz_pl wrote on 2022-07-09, 12:50:

short on power rail would mean no 5V, if you measure 5V there is no short on power […]
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butjer1010 wrote on 2022-07-09, 12:01:

It is not hot, it is cold after 3 minutes?!?
How can i check is there a dead short on 5V rail? You meant on PSU connector or on SIS chip?

short on power rail would mean no 5V, if you measure 5V there is no short on power

butjer1010 wrote on 2022-07-09, 12:01:

between B4/B6 on ISA - 3.88kOhm

between ground and B4 is 3Kohm, and B6 and ground same?

butjer1010 wrote on 2022-07-09, 12:01:

Weird thing is when i measure 5V on isa B1 and B29 pin, now it is normal - 5V, and before i made a mess, there was 2.55V???

most likely explanation: because yesterday you measured B30 by accident instead of B29, its a clock signal oscillating between ground and 5V therefore might show as 2.5V on the meter. Its even possible you shorted B30 to B29 blowing the oscillator

butjer1010 wrote on 2022-07-09, 12:01:

Do You have schematics of 206 chip, so i can see 5V rails on chip?

I see SIS calls this 85C206 and not standard 82c206
http://www.bitsavers.org/components/opti/dataSheets/
Page 6 http://www.bitsavers.org/components/opti/data … ller_199608.pdf
you will have to sanity check if its the same pinout. Easiest is looking at VCC and GND pins and checking if they are wired to ground/power as in the datasheet, then moving to IRQ pins and corresponding ISA signals etc

butjer1010 wrote on 2022-07-09, 12:01:

If i manage to solve this 206 chip problem, i will desolder ram slots to see if there is some broken trace.

two options
1 difficult and prone to failure (melted sockets, ripped traces): desoldering
2 imo easier: going pin by pin with documentation and checking continuity while making notes. this means you will have to force yourself to understand https://alexandrugroza.ro/microelectronics/sy … c-schematic.png 😀

butjer1010 wrote on 2022-07-09, 12:01:

100 times thanks man, You've been very helpfull, sorry if i have took Your time.

helping people fix old gear is fun
if you really want to fix this particular board, and I would understand giving up 😀, you will need a $5-10 ISA POST card at the very least. $10 "USB Logic Analyzer 24MHz 8 Channel" wouldnt hurt either, but $50 16 channel is preferable. It quickly starts to add up and becomes uneconomical for a one off deal, doesnt make sense if its not your hobby. That or access to hackerspace with proper gear.

between ground and B4 is 3Kohm, and B6 and ground same?
No, i have measured between b4 and b6. Ground and B4 - 6.67kO, and ground and B6 - 1,76kO

most likely explanation: because yesterday you measured B30 by accident instead of B29, its a clock signal oscillating between ground and 5V therefore might show as 2.5V on the meter. Its even possible you shorted B30 to B29 blowing the oscillator
Sounds true, because i measured 77th i 78th pin on sis chip, and there is 5.01V, so maybe i didn't fry sis chip 😀

doesnt make sense if its not your hobby
Yes, i'm having my coputer service for almost 15 Years (majority of work is changing ssd for old hdds, installing Windows, fixing hinghes on new laptops 😀 ), but i live in village with 14000 people, and nobody here, except me, is collecting old DOS computers. I'm the only one loving working in DOS, and playing old dos games. I started to collect old computers (286-PIII, and commodore, amiga, atari,....) before 2 years. I have nice collection, but i do this for my fun, not for money, and i didn't need any of this POST cards until this board.

two options
1 difficult and prone to failure (melted sockets, ripped traces): desoldering
2 imo easier: going pin by pin with documentation and checking continuity while making notes. this means you will have to force yourself to understand https://alexandrugroza.ro/microelectronics/sy … c-schematic.png 😀

I tried, using this schematics, to test the traces between RAM sockets (on the lower side of board), and they are all fine, but with this schematics, i cannot figure where they are going to CPU or on other chips. CPU pins on this schematics are not numbered same as on my motherboard, so i cannot test them if they have continuity to other chips on motherboardboard.

SIMM rams do not connect straight to CPU, its DRAM and needs memory controller - the chipset.

SIMM1/CON1 pin 3 D0
82C495XLC pin 34 HD0

SIMM1/CON1 pin 4 DBMA0
resistor ladder RA5A DBMA0 -> BMA0
74F244 BMA0 -> MA0
82C495XLC pin 89 MA0

this diagram is most likely not an exact 1:1 match for your board, but the layout is straight from chipset manufacturer reference design so its going to be very close. Things like buffer chips (74F244/245) pinouts wont match, but the overall logic will. BTW address and memory bits dont need to be router 1:1 as designated. For example manufacturer can route D1 (data bit 1) on chipset to Simm socket DQ7 if that makes for an easier layout. That means you have to make sure chipset pin 34 (HD0 = D0 = data bit 0) connects to one of SIMM socket DQ pins pins (https://allpinouts.org/pinouts/connectors/mem … am-simm-30-pin/ 3,6,10,13, etc)

rasz_pl wrote on 2022-07-10, 19:31:

SIMM rams do not connect straight to CPU, its DRAM and needs memory controller - the chipset. […]
Show full quote

SIMM rams do not connect straight to CPU, its DRAM and needs memory controller - the chipset.

SIMM1/CON1 pin 3 D0
82C495XLC pin 34 HD0

SIMM1/CON1 pin 4 DBMA0
resistor ladder RA5A DBMA0 -> BMA0
74F244 BMA0 -> MA0
82C495XLC pin 89 MA0

this diagram is most likely not an exact 1:1 match for your board, but the layout is straight from chipset manufacturer reference design so its going to be very close. Things like buffer chips (74F244/245) pinouts wont match, but the overall logic will. BTW address and memory bits dont need to be router 1:1 as designated. For example manufacturer can route D1 (data bit 1) on chipset to Simm socket DQ7 if that makes for an easier layout. That means you have to make sure chipset pin 34 (HD0 = D0 = data bit 0) connects to one of SIMM socket DQ pins pins (https://allpinouts.org/pinouts/connectors/mem … am-simm-30-pin/ 3,6,10,13, etc)

What do You think, after all we wrote up there, is it worth to change sis chip for opti82c206, and be on beginning, or not?
Thanks

As a learning experience fully aware this is a sacrificial board? why not.
I dont know how to put it in a nice way. I think that watching YT clips of people changing QFP chips effortlessly doesnt translate into ability to do the same. You have trouble reading diagrams and lack confidence measuring stuff with 2.5mm gaps between legs 🙁, but rush to taking off SIMM sockets or replacing 0.5mm pin pitch chips.

We dont even know what you did to break the board further, and if its this chip that is defective.

rasz_pl wrote on 2022-07-11, 15:50:

As a learning experience fully aware this is a sacrificial board? why not.
I dont know how to put it in a nice way. I think that watching YT clips of people changing QFP chips effortlessly doesnt translate into ability to do the same. You have trouble reading diagrams and lack confidence measuring stuff with 2.5mm gaps between legs 🙁, but rush to taking off SIMM sockets or replacing 0.5mm pin pitch chips.

We dont even know what you did to break the board further, and if its this chip that is defective.

I'm not that bad in soldering 😀 I've changed smaller chips so far (realtek sound chip on motherboard), so it is not the problem This is something i do often. I did something bad in 2 a.m., without glasses (i don't know why i tried anything without them), i'm not even sure if i connected 2 isa pins, but after "testing", motherboard did shut down, so i suppose i did that. I don't know how to read diagram, i'm not IT expert, i have finished high school in 1996, but after 15 Years doing everything to survive, i started to fixing computers. As a hobby first. I don't watch YT clips to know how to fix old motherboard, i ask questions here, and i receive answers from people who knows a lot more than i do (like You). I wouldn't ask You if it's smart to change chip if i don't know how to do it.
Thanks man, i have learned a lot from You, and i hope i will learn more from people like You.

start by acquiring POST card, trying to replace anything blind is unproductive
if 85C206 is indeed bad and preventing boot you will be able to see it in the POST codes generated before and after taking it off.

rasz_pl wrote on 2022-07-11, 20:35:

start by acquiring POST card, trying to replace anything blind is unproductive
if 85C206 is indeed bad and preventing boot you will be able to see it in the POST codes generated before and after taking it off.

Can You send me link where to buy some "good" post card. I tried to find it on ebay, but they all seems to be the same (more than 100). Is there any difference between them?
Thanks a lot

makes no difference in your case. You need _anything_ to see whats going on. Is the CPU running at all? Where is it stopping?

You can also make your own if you like - its in that same motherboard diagram in lower left corner. It takes 3 chips (574,688, and one with OR/NOR gates)
other variations:
http://www.malinov.com/Home/sergeys-projects/isa-post-card
https://www.andavno.com/pdf/ISA_POST_BOARD_v2 … 0_SCHEMATIC.pdf

its all the same idea, grab 8bit value from the data bus when lower Address lines equal 0x80h (10000000) and active IOW signal. You can use salea clone as a readout instead of led displays and decoders.