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S100 8088 CPU Board Crashing/Unstable

Hi everyone,

I've recently plugged my 8088 CPU board into my S100 system and have been having problems with the 8088 CPU board crashing/locking up.
My system comprises all S100Computers.com boards

Prop I/O Console V01
16MB V3 Static Ram Board
V2 MSDOS support board
V2 Z80Master CPU Board
V1 8088 CPU Board (Slave)
V1 ZFDC Floppy Controller
V2 S100 IDE/CF Board

The 8088 board was inspected for damage before construction, All resistors/capacitors/sil arrays are new & checked with multimeter/capacitance meter before soldering to the board,
All TTL logic chips (TI branded) are new, all jumpers were initially set as per Johns webpage and double checked and the 3 x 47pf capacitors are in the correct locations.

The symptoms are similar to what AltairManRich had been experiencing in a few previous posts but no conclusion has been posted.

Basically, I can boot my system into the Z80 monitor and transfer control to the 8088 CPU which signs on with it's banner, I can press 'K' and bring up
the monitor menu, most monitor commands seem to work fine but menu option 'J' memory test (specifying 1000,2000 as parameters) always results in the 8088 CPU card going into LaLa Land
as Rich puts it, just filling the screen with spaces and scrolling, only a hard reset recovers the system. Occasionally the 8088 CPU will go into a HALT state rather than scrolling spaces.

I can 75% of the time get the 8088 CPU card to boot MSDOS 4.01 sometimes it hangs but most of the time I can get a directory listing, but copying a file to a folder will cause the
system to freeze, also running the MSDOS command MEM always results in a system lockup.

If I drop the 8088 CPU card out of the system and place my 80286 card into the system everything mentioned above works fine without an issue so the fault would seem to be on the 8088 CPU board.

Studying the jumpers and schematic I can improve matters if I jumper K5 2-3, K6 2-3, K7 2-3, K11 2-3, K13 2-3 which obviously is tweaking the bus signal timing to come more from
U68 the bus controller IC, the monitor memory test 'J' then seems to work fine but the system is still not totally stable under DOS and I can get it to crash. Lowering the CPU speed to 4.77Mhz makes no difference the fault remains.

My CPU is a Fujitsu MBL8088-1 and the bus controller IC is a UMC82C88, both of these IC's were supplied as 'NOS' but I can't remember the vendor now. 
I also have a NEC V20 CPU I have just had delivered from UTsource, if I fit this IC then the system stability is much worse

So I have now ordered a 'NEW' Intel 8088-2 and a 'NEW' AMD8288 (non-cmos) bus controller to see if that changes the situation.

Are there any other recent 8088 CPU board builders having problems with this board ?
Rich, did you fix your board ?


David Fry