Uncreative Labs

Joined: 20 Nov 2004 Posts: 589 Location: Shandong, China

It's been a pretty long time since I last played with my XT. But, I dug it out the other day and tried to fix some of the problems I was having previously. Here's the jist of what's going on:

I originally intended to stick with my original IBM 5160 motherboard, but after I bought a high density floppy drive controller for it I discovered they didn't want to work together. It's this damn MCT High Density 4 floppy drive controller (ABLY TECH) that I bought from JDR. When plugged into my XT motherboard the POST is really slow, and it won't read high density disks at all. I've tried everything, and I just can't get it working.
So, I decided to buy a Juko 15MHz v30 motherboard to replace the original system board. This Juko board is really nice, but the stupid thing just doesn't work very well. There is something wrong with the keyboard controller. I've tried it with 5 different keyboards. No matter what I do I recieve keyboard errors at boot. The only way to get it working is to unplug and reconnect the keyboard after boot.
I did some benchmark testing under PCTools version 8 SI. The CPU is about the same speed as an 8MHz 286. I threw a lot of VGA games at it, and it was indeed quite fast. The MCT controller kind of works in this board, although rather slowly....and also I can't boot. Booting from a floppy locks up the machine. Thanks for nothing MCT. Additionally, incase some of you might be concerned this v30 board runs its PC BUS slots at 7.4MHz on a separate crystal.
So basically I am in the market for both a new HD floppy controller, and a turbo XT motherboard. I figure 10MHz is the way to go, unless I can find a 12MHz board with an asyncronous bus.

Joined: 03 Feb 2006 Posts: 488 Location: pennsylvanai

i worked on a juko 12 mhz xt board onece
and it had a v-20
there is a faxst v20 program to get a few more clicks out of it.
I had a dtk high density 4 floppy xt card.
I returned it as it would improperly format 720k disks and make them unusable when the switches were set for the 1.44.
another card worked better
-- with a clone xt mb

Joined: 19 Apr 2006 Posts: 261 Location: WisConSin

That is the exact behavior my one Motorolla 68010 would exhibit when I tried to push the board past 14.xxmhz apparently the keyboard controller flaked out above that and the keyboard data transfer rate (to the keyboard itself) was out of range.

Maybe something similar going on or perhaps you have a bad trace going to the keyboard port and it will pop one of these days.

Joined: 20 Nov 2004 Posts: 589 Location: Shandong, China

I figured out the problem with this board. It seems that a solder joint, or part of the keyboard port is broken. Wiggling it a little seems to fix it. I'll have to repair or replace that later. Also, it seems this board doesn't like model M keyboards. Hopefully the model M will become usable after the port is fixed.

I also tried changing the frequency of the CPU. This board is using an NEC V30 10MHz that is overclocked to 15MHz by the manufacturer. It is surprisingly stable. However, this poses a problem if you want to use an FPU. I tried an 8087-1 which is the fastest rated FPU for an 8088/8086 system. It doesn't work at 15MHz. It doesn't work at 12MHz. Even if the program doesn't specifically use the FPU it will eventually crash the system. Turning off turbo drops the speed of the board to 8MHz (I think), which is okay. But, because the ISA bus is clocked at half the CPU speed this gives just 4MHz which is kind of slow. My solution for now is to just run without the FPU. At 15MHz, the emulated FPU isn't much worse than a 5MHz 8087.

Though, it would be nice to use a real FPU. I wonder if there is a clock halving circuit that can be made for this purpose. An 80c87 might work at 15MHz, but probably not....and hard to find. A Cyrix 8087 would probaly work, but I think those were vapourware...and 80187s only work with 80188. So, I think a special circuit is my only real option.

Right now the other two big issues for this system are the high density floppy controller and the flash drive. The floppy controller must have a bad ROM. It has never worked on any system I tried it on...ever. The flash drive is half working. As far as I can tell the IDE to CF adapter is just very poor quality, and there is a loose connection in there somewhere. Sometimes it works, sometimes it doesn't. The SCSI to IDE bridge has been tested with other devices and works great.

Also, I have the Orchid RAMQuest board with 32MB installed and runnning. It works quite well, though I need to get some interesting software that can make use of it. Right now I find it difficult to get files on my XT because the high density drive is inoperable, networking is not possible (no way to run a cable to the basement), I'm out of CD-Rs, and the flash drive is not reliable. But, when I get around to fixing one of those things I'll be sure to try it out.

Joined: 20 Nov 2004 Posts: 589 Location: Shandong, China

I found a replacement high density floppy controller for this system, but unfortunately it won't arrive until I'm back at work. I hope everything will go smoothly, unlike the one I got from JDR. I have a feeling the ROM on my card is probably bad. I'll have to try burning a new one for it later.

I didn't get around to installing a new keyboard port on the V30 board as I was too busy trying to repair a 5175 PGA display (made some progress, but still no picture). By wiggling the connector enough I was eventually able to coax a model M keyboard to work with this sytem. BUT...not the XT model M. It seems that mine has a problem. When hooked up to other machines I found it sometimes spits out garbage. I'll figure that one out later. If worst comes to worst, I'll just swap out the PCB with a newer model M. I seem to be having a hell of a time with dead stuff these days.

Speaking of dead electronics...I found that my original XT power supply was not dead, but there is infact a short someplace on the original 5160 planar. I am not sure why the second XT power supply allowed it to boot up, but I noticed the system behaves strangely. It consistently failed at writing some images via teledisk. I have another XT motherboard, but I'd like to fix this 640k board if possible.

Finally, I didn't mess with my SCSI --> CF card much at all. I've come to the conclusion that the quality of my adapter is crap (I think I paid $1 for it). For next time I'll have to stock up on several different versions of the IDE to CF adapters to make sure I get one that is compatible with SCSIDE. I don't want to buy one in the US since I'll end up getting screwed by the markup and shipping.

That's about all I can do with the XT for now. It's back in a box full of packing peanuts for the next six months.

Joined: 03 Feb 2006 Posts: 488 Location: pennsylvanai

it could be the original cpu is a 8088 and that works with a v20
the 8086 "xt class" systems were rare and required a v30 to replace the 8086.

tghe juko boards I remember had v20 cpu's as the
8088 was only designed to work at 10 mhz

avoid the DYK 8088 boards as they have some problems.

the xt and at used different keyboards
early models had a switch ( soletimes hidden )
some later models auto-switched
and even later kb would simply not work with a 8088 class mb.

also remember that early IBM pc's had a bios that did not "look" for bios extensions
like a ega/vga card, a hd controller, or an advanced floppy card.
One of the best hd floppy cards was the IOS-2
pale gray and blue box, a 4" square card with a
silver clock battery ( 25cent sized) on it,.

no you cannot have my last one.

Joined: 20 Nov 2004 Posts: 589 Location: Shandong, China

The Juko boards are available in a number of versions. I have seen 8MHz, 10MHz, 12MHz and even 15MHz (like mine). There are V20 and V30 versions available for ever speed rating except 15MHz as far as I know. Mine is definitely a V30 version. I tried to clock it lower than 15MHz, but doing so slows down other parts of the machine too much. If I could figure out how they divide up all the clock signals for the various components I might be able to do something about it. I'm thinking a 10MHz board would be ideal, since 8-bit ISA is best at 10MHz and I could still use the 8087-1.

Are the DTKs really that bad? I know that the DTK 286 and 386 are no good, but do their XT boards have a funky BIOS as well? I just assumed they used Phoenix like everyone else.

Joined: 03 Feb 2006 Posts: 488 Location: pennsylvanai

I went to dtk in edison and they cut a pin on a chip
to stop the pck- and sparkles all over the screen
If i can recover that info I will post it
I think I got rid of all the dtk mb,
another problem was the bios
it was written by "the damn taiwanese government" their words not mine! and was supposed to be 100% compatable.
i think the phoenix bios was better.
the dtk pentium board I had did not like the adaptec scsi card but another brand would work.
the pci 2940 was a problem , but another isa card worked. the board had 2 markingsm the dtk and another name
flashing to the other bios fixed that problem
but it had both DYK and another name on the board
think it was a sub p233 mb.

getting back to 8088's
many of the really old cards for ther pc/xt would crash at even an 8 mhz bus
a i/o board for a 286 ( not an ide i/o)
would work as well as the ibm at serial/parallel board ( 1 of each)
a 16 bit vga card will often work in an 8 bit slot.