Can't find anything yet in TH99, but I'll have an educated guess for the switch block:

1Parity ram ??
2Enable or Disable numeric coprocessor
3Floppy drive switch 1 (can be 1,2,3 or 4 drives)
4Floppy drive switch 2
5Display switch 1 (probably MDA/CGA (40 or 80 col.) /VGA
6Display switch 2

For switch 1 and 2 settings, you can have a total of four combinations to try (00 ,01 ,10, 11).

If nothing works out, I recommend making a Ruud's Diagnostics ROM and test the board with an LPT debug card, the standard ISA debug card will not work in a XT.

computerguy08 wrote on 2020-08-17, 16:36:

Can't find anything yet in TH99, but I'll have an educated guess for the switch block: […]
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Can't find anything yet in TH99, but I'll have an educated guess for the switch block:

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1Parity ram ??
2Enable or Disable numeric coprocessor
3Floppy drive switch 1 (can be 1,2,3 or 4 drives)
4Floppy drive switch 2
5Display switch 1 (probably MDA/CGA (40 or 80 col.) /VGA
6Display switch 2

For switch 1 and 2 settings, you can have a total of four combinations to try (00 ,01 ,10, 11).

If nothing works out, I recommend making a Ruud's Diagnostics ROM and test the board with an LPT debug card, the standard ISA debug card will not work in a XT.

Thanks for info.i hear only a short beep and keyboard numlock capslock are working no any other signal

You can try messing around with the display switches 1 and 2.

Alternatively, you should try other VGA cards, some don't work in 8-bit mode.

Update:Board working after reflashed JUKO ST 2.3 bios.but after two power recycle no post again? What is the problem?
Im sure that this board is late clone of juko st.

As I said, a diagnostic ROM will help you narrow down the defective components. Otherwise, you will waste a lot of time guessing. I'm saying this because I did the same mistakes fixing my turbo XT board.

It could be anything: bad socket contact, bad DRAM refresh circuitry, bad EPROM, etc.

Try the SuperSoft/Landmark Diagnostic ROM.
You do actually need a CGA or MDA card to properly view the results on screen.

update: With Landmark diagrom(landmark)
Continiously 1 high and 1 low beeping.

Read this:

http://www.minuszerodegrees.net/supersoft_lan … rs%20Manual.pdf