I have a similar and working (but not identical) Juko XT board that I could dig up if you need some particular measurement for comparison, and indeed it doesn't produce POST codes on the typical port 80 diagnostic cards even when operating correctly.

As for the 48Ω impedance you're seeing on your AT PSU, it could be an internal minimum load resistor for the +5V rail you're indirectly measuring, not an uncommon thing.

133MHz wrote:

I have a similar and working (but not identical) Juko XT board that I could dig up if you need some particular measurement for comparison, and indeed it doesn't produce POST codes on the typical port 80 diagnostic cards even when operating correctly.

As for the 48Ω impedance you're seeing on your AT PSU, it could be an internal minimum load resistor for the +5V rail you're indirectly measuring, not an uncommon thing.

Thanks for the input!

I thought the behavior with low resistance with an unpowered PSU connected could be normal but as it wasn't exactly the same as in my working system I wanted confirmation. An internal minimum load resistor sounds very logical so I guess the princess is in another castle. 😀

If this ends up beeing memory incompatibilty with 44256 chips I will be somewhat irritated but I can't just make my self buying the expensive DIP-19 "MB81C1000-10 1Mx1bit DRAM" chips I have been suggested could work with this board as I have loads of 44256 chips and this is what most late XT clone boards use. I rather buy a "Lo-Tech 1MB RAM board" as I could use that in my other XT systems which only have 640KB to get some UMB space if this board should end up beeing unsalvageable.

I should perhaps add that the video card I'm using is 8bit/PC-XT friendly and the CPU is also tested. On the picture the Nec V20 is still on the board but as I now use that CPU with my working machine this board is now equipped with the 10 MHz capable AMD 8088 that came with the working system. I have also tried the parity dip switch in both positions.

Dumping the BIOS did not turn out to be as easy as I hoped.

Uniflash won't work with my XT clone, not in DOS 3.3 and not in DOS 6.22.

Is there some good tool for an XT class system that can make a BIOS dump or do I need an external reader/writer?

Skyscraper wrote:

If this ends up beeing memory incompatibilty with 44256 chips I will be somewhat irritated but I can't just make my self buying the expensive DIP-19 "MB81C1000-10 1Mx1bit DRAM" chips I have been suggested could work with this board as I have loads of 44256 chips and this is what most late XT clone boards use. I rather buy a "Lo-Tech 1MB RAM board" as I could use that in my other XT systems which only have 640KB to get some UMB space if this board should end up beeing unsalvageable.

It's pretty disappointing when things don't work. I too was a bit baffled when my Juko board didn't work with 44256 DRAM. The 1MB RAM card from lo-tech is indeed a solution and maybe you can save some bucks if you build it yourself. Still with the cost of PCB + parts + shipping to Sweden i'm not sure it will be cheaper than the outrageously expensive old 1MB x 1 DRAM chips. It is also a card that requires much harder work/effort due to those annoying SMD resistor networks. However it's a card that can provide not only 640KB memory but also upper memory blocks. So although more expensive its a much better investment overall, and can always be used in other systems as well.

I will be looking into getting one of these Juko Nest boards too, but i want the 8086 version which Anonymous Coward/Robin4 own.

NSSI can sometimes dump the BIOS; http://www.navsoft.cz/products.htm

But I am unsure of it it runs on the 8088. Can't hurt to try. Otherwise, you can try using DEBUG and doing it manually, but you might have to fiddle with parameters and I can't remember the specifics...

http://www.mess.org/dumping/dump_bios_using_debug

carlostex wrote:

Skyscraper wrote:

If this ends up beeing memory incompatibilty with 44256 chips I will be somewhat irritated but I can't just make my self buying the expensive DIP-19 "MB81C1000-10 1Mx1bit DRAM" chips I have been suggested could work with this board as I have loads of 44256 chips and this is what most late XT clone boards use. I rather buy a "Lo-Tech 1MB RAM board" as I could use that in my other XT systems which only have 640KB to get some UMB space if this board should end up beeing unsalvageable.

It's pretty disappointing when things don't work. I too was a bit baffled when my Juko board didn't work with 44256 DRAM. The 1MB RAM card from lo-tech is indeed a solution and maybe you can save some bucks if you build it yourself. Still with the cost of PCB + parts + shipping to Sweden i'm not sure it will be cheaper than the outrageously expensive old 1MB x 1 DRAM chips. It is also a card that requires much harder work/effort due to those annoying SMD resistor networks. However it's a card that can provide not only 640KB memory but also upper memory blocks. So although more expensive its a much better investment overall, and can always be used in other systems as well.

I will be looking into getting one of these Juko Nest boards too, but i want the 8086 version which Anonymous Coward/Robin4 own.

Price is not really the main issue for me, price vs "value" is as I'm a genuinely cheap person! 🤣

[Rant]

With the 1MB RAM card you at least get something unique, not a few mermory chips doing exactly the same thing as 44256 chips but costing 5 times as much. If I have to pay at least as much for memory chips as for a working XT clone board including 1MB memory then that just dosn't make sense to me, especially as I dont even know if this board works.

I already have two other working 10 MHz "Turbo XT" boards although with only 640KB memory (and no support for more) but for now they are good enough. I'm not even sure what software the XT clone can run that needs more memory than I will end up with after loading the needed drivers. Still I rather pay what ever an 1MB ram card will end up costing if someone decides to build a few than pay the ~60 euro these memory chips would end up costing with shipping and Swedish VAT + handling fee.

[/Rant]

I'm also looking for an 8/10/12 MHz 8086 XT clone board but this is not very high in my priority list.

Except for deals too good to turn down or I really need a specific item I'm not spending any more money on hardware until the summer is over (that is at least the plan).

HighTreason wrote:

NSSI can sometimes dump the BIOS; http://www.navsoft.cz/products.htm

But I am unsure of it it runs on the 8088. Can't hurt to try. Otherwise, you can try using DEBUG and doing it manually, but you might have to fiddle with parameters and I can't remember the specifics...

http://www.mess.org/dumping/dump_bios_using_debug

Thanks for the tip.

I will try NSSI but I will leave debug be for now as I'm not even sure what size the BIOS is.

If NSSI does not work I will probably try to dump the chip with an Intel 430VX chipset motherboard (if it can support the chip) the next time I need to hotflash a BIOS for some dead board.

[Edit]

NSSI does not seem to be able to dump the bios on XT class hardware. The GUI portion of NSSI does not run at all but the program does list the hardware in text mode.

At least I now know that this Juko Nest BIOS is from 03-07-90.

[/Edit]

Sorry, for invading you thread, but maybe i can help.
I've had got a similar issue with my pizza box 286 a while a ago..
Found a few utilities. One of them worked for me, so maybe does one for you.

Jo22 wrote:

Sorry, for invading you thread, but maybe i can help.
I've had got a similar issue with my pizza box 286 a while a ago..
Found a few utilities. One of them worked for me, so maybe does one for you.

Thanks! I will try them.

I would not call helping and adding useful information + utilities for invading! 😀

Here comes the BIOS dump.

The file is 256KB as the whole BIOS area got dumped so I guess alot of nothing needs to be removed.

Out of the data some of it could very well be the VGA BIOS from the OTI-037c video card and some of it could be the XT-IDE BIOS. With luck someone who is familiar with BIOS editing can make sense of it and sort it out for us.

Right at the end of the file there is a "VEGAS Computing Solutions" BIOS which seems to be what you're after

Of course, without my own system to test it on, I can't be entirely sure this is correct or not. There are other ROMs in the file, such as XTIDE, Multi-Floppy BIOS and what appears to be an OAK VGA.

Actually seems the BIOS may be only 8KB and was in the file twice, if you really want me to check and then remove the last 8KB if this turns out to be the case, I will.

It does seem 8KB is average for an XT BIOS, so I've cut away half of the file;

I hate that we can't upload BIN files here.

The JUKOVEGAS.zip should be correct. 16k -> the EPROM will be a 27128 then.
The output of POST codes depends on the BIOS, it's possibly not implemented or goes to a different port. As the BIOS works in another board you could check what the POST card does there.
About the 48 ohms: The power supply probably has an internal resistor as minimum load. As long as it delivers 5V there's no problem.

- Tried a PC speaker?
- Do you have the 5 volts when powered on?
- parity chips are in place?
- Pin 21 of the 8088 has which voltage relative to GND?
- The VGA card is not the one that loves to play dead? 😀

An advanced diagnostic method is http://www.minuszerodegrees.net/supersoft_lan … dmark%20ROM.htm
You happen to have a logic probe or other suitable instrument? http://www.eleccircuit.com/many-logic-probe-circuit-ideas/

Nice!

With luck this is what member Anonymous Coward needs.

Perhaps he can report if it works. 😀

h-a-l-9000 wrote:

The JUKOVEGAS.zip should be correct. 16k -> the EPROM will be a 27128 then. The output of POST codes depends on the BIOS, it's p […]
Show full quote

The JUKOVEGAS.zip should be correct. 16k -> the EPROM will be a 27128 then.
The output of POST codes depends on the BIOS, it's possibly not implemented or goes to a different port. As the BIOS works in another board you could check what the POST card does there.
About the 48 ohms: The power supply probably has an internal resistor as minimum load. As long as it delivers 5V there's no problem.

- Do you have the 5 volts when powered on?
- parity chips are in place?
- Pin 21 of the 8088 has which voltage relative to GND?
- The VGA card is not the one that loves to play dead? 😀

An advanced diagnostic method is http://www.minuszerodegrees.net/supersoft_lan … dmark%20ROM.htm
You happen to have a logic probe or other suitable instrument? http://www.eleccircuit.com/many-logic-probe-circuit-ideas/

- As the BIOS works in another board you could check what the POST card does there.
This I have already done and the diagnostic cards shows "FF" and nothing more in the working system with the Juko BIOS, in the Juko board it shows "--"

- Do you have the 5 volts when powered on?
At least I though so as the 5+ V led on the diagnostc card is lit.

- Tried a PC speaker?
No, I dont know what header it goes on, J5?

- parity chips are in place?
No, as I am not 100% sure of the bank layout. I have tried to disable partity with dip switch 1 (tried both on and off). I could test to fit some 4464 in the most likely sockets.

- Pin 21 of the 8088 has which voltage relative to GND?
I will check this.

- The VGA card is not the one that loves to play dead? 😀
No. Ths VGA card is working and I have tried more than one. The VGA BIOS included in the dump is from the funky card though. This card cold boots fine with a LCD now but the picture degrades with time, on the CRT the picture does not degrade...

- You happen to have a logic probe or other suitable instrument? http://www.eleccircuit.com/many-logic-p ... uit-ideas/
That would be a no, it has been 15 years since I last did anything more advanced than looking for shorts and replacing caps (and blown transistors in amps).

The JUKOVEGAS file seems to be repeating the same first 8KB.

carlostex wrote:

The JUKOVEGAS file seems to be repeating the same first 8KB.

Perhaps that is as it should be if the BIOS chip is 16KB?

Yes, it is repeating, I haven't seen that. For a 2764 chip use only one half.

Speaker: One pin should have 5V, the other may go through a resistor (like 33 ohms) to the collector of that transistor.
What does the documentation of the POST card say about '--'?

h-a-l-9000 wrote:

Yes, it is repeating, I haven't seen that. For a 2764 chip use only one half.

Speaker: One pin should have 5V, the other may go through a resistor (like 33 ohms) to the collector of that transistor.
What does the documentation of the POST card say about '--'?

"--" is what the diagnostic card shows when there is nothing to show. It's not in the manual but when a motherboard has no BIOS at all or an non working BIOS or for some other reason does nothing the card shows "--".

The voltage leds for +5V +12V and -12V are lit as are the leds for "CLK", "IRDY" and "FRAME" but not "RESET". On the other hand the led for +3.3V is also lit so I would not trust the card alone...

I just chacked the voltages. +5V is reads fine, the 8088 has +5V on pin 40 (VCC) , and 0V on pin 21 (reset)

The headers read [0V - +5V] [+5V - 0V] [+5V - +1V] [+5V - 0V] [+5V - 0V] and [+5V - +5V] (Pin to GND)

The one my intuition thought was the speaker one (J5) is the one reading [+5V - +1V] , it has the transistor right behind it. With speaker connected over these two pins both reads +5V measured to GND, at least there were no magic smoke escaping...

Edit

I have also added 4464 chips to what I would imagine is the first 4 parity sockets.

It's only the "RESET" led that isnt lit on the diagnostic card, not "FRAME" as I first wrote.

/Edit

I'm attaching my guess at the banks. Not sure if the 128k bank must contain something. Depends on which block starts at address 0.
If you have a piezoelectric speaker (no conductivity across it) you can try every header without danger.

So the 8088 is not held in reset and may be executing code.
FRAME appears to be PCI related.

h-a-l-9000 wrote:

I'm attaching my guess at the banks. Not sure if the 128k bank must contain something. Depends on which block starts at address […]
Show full quote

I'm attaching my guess at the banks. Not sure if the 128k bank must contain something. Depends on which block starts at address 0.
If you have a piezoelectric speaker (no conductivity across it) you can try every header without danger.

So the 8088 is not held in reset and may be executing code.
FRAME appears to be PCI related.

That was actually how the 4x 44256 chips the board came with was placed, it came with only 512KB and no parity chips though. I filled all 8 sockets as I did not know the bank layout, 8 DIP-20 sockets for 8 44256 felt logical. 😀

When I said above that I filled the parity sockets with 4464 that was of course incorrect, I got the chip types mixed up (as I often do), I of corse meant 4x DIP 16 41256, they were the 4 parity chips on a 12 MHz 286 board using 8 44256 for 1MB memory.

I will try using only 4x 44256 with and without parity chips and I could borrow 4 actual 4464 chips from my working XT clone but I doubt I have any 4164 to use as parity for the last 128KB memory except perhaps in my NEAT chipset 286, can I use 41256 chips as parity for the 4464 chips aswell?