Does anyone have this board?

I would appreciate any help to at least test this motherboard.

SDumas

SDumas wrote on 2023-11-03, 16:25:

Does anyone have this board?

I would appreciate any help to at least test this motherboard.

SDumas

I have one. Dont know it's status. I also dont have a eeprom reader. Its also a 001 rev g

bobconan wrote on 2023-11-18, 07:55:

SDumas wrote on 2023-11-03, 16:25:

Does anyone have this board?

I would appreciate any help to at least test this motherboard.

SDumas

I have one. Dont know it's status. I also dont have a eeprom reader. Its also a 001 rev g

Hi bobconan,

Thank you for responding to my request for help.
Do you know anyone nearby, who has an eprom reader ?
I think this is the only way it will be possible to have a bios copy from
your motherboard.

By the way, where do you live?

SDumas wrote on 2023-11-03, 16:25:

Does anyone have this board?

I would appreciate any help to at least test this motherboard.

SDumas

Hi SDumas,

I do have a "001 REV G" board - found it on the curb about two months ago. I didn't have the opportunity to test it yet but may have managed to read out the 16K EPROM.
A hexdump of the attached BIOS file indicates that it's version 3.2/3.28 from April 29th, 1986.

Best regards

Hi jcmb,

Thank you very much for the great help you are giving me.

I'm going to program an eprom and test it, I'll see if I can do it today.
I will then give feedback on the results.

All best regards
SDumas

jcmb wrote on 2024-06-06, 22:00:

Hi SDumas, […]
Show full quote

SDumas wrote on 2023-11-03, 16:25:

Does anyone have this board?

I would appreciate any help to at least test this motherboard.

SDumas

Hi SDumas,

I do have a "001 REV G" board - found it on the curb about two months ago. I didn't have the opportunity to test it yet but may have managed to read out the 16K EPROM.
A hexdump of the attached BIOS file indicates that it's version 3.2/3.28 from April 29th, 1986.

Best regards

Do you have the original power supply for this motherboard?
It is necessary to pay attention to the pinout of the connector because it is not standard.
See attached photo.

If necessary, I can provide the pinout to make an adapter from an AT power supply.

Best regards

Hi jcmb, i have good news,

The motherboard is alive, at least I know that now...

I tested it without a keyboard, just with a graphic card and it boot fine.
I don't have an XT keyboard at the moment.

I have one, but I don't know where it is, I'll have to look for it when I have time...

For now this motherboard will remain on standby until I find time to test it with a Floppy and hard drive.

For BIOS setup I think i´ll need some software on a boot disk.

I'll come back to this thread when I have some news...

And once again, thank you very much for the bios file.
Best regards
SDumas

Hey SDumas,

that's great news and you're welcome. 😀 I'm glad I could help so far.
Here are my thoughts on a planned hardware setup. If you could just post yours as well, that'd be extremely helpful. Thank you!

Power supply:
I did find the power connector's pinout in some reddit post and verified by the very same YouTube video from your screenshot. 😁
I'm thinking about using a picoPSU for testing and sacrificing an ATX connector to directly attach the corresponding supply lines.

Graphics adapter:
I have a 1990-ish era 16-bit ISA VGA card but I'm unsure if that would do the trick.
It's an Oak OTI-077 and I'm unaware of compatibility with the shorter 8-bit slots (or even the architecture as a whole).

Lack of XT keyboard:
I think any (cheap) micro controller solution plus some breadboarding "magic" would manage.
For example there is a promising one on GitHub using a RaspberryPi Pico.

Compatible (E)EPROMs, Storage and OS:
I believe there's a lot of potential with XTIDE and the additional EPROM slot(?) above the BIOS chip.
FreeDOS seems to be compatible with 8088...

Looking forward to your future findings!

Best regards

Since I have an XT keyboard, I won't have any problems testing any old motherboards

I don't have much experience with XTIDE, I only used it once to do some tests.
My problem is the lack of time to do all these experiments.

As I have some old MFM hard drives in good condition, I'm going to use them to test this motherboard, but I don't know when...we'll see...

Since there is not enough information, I have doubts about the maximum capacity of the floppy drive controller.
This motherboard came with a 360KB 5 1/4 floppy drive.

Can i fit a 1.44MB 3.5 floppy disk drive?

If anyone needs the pinout for the power connector of this motherboard, I'll put it here anyway...
See the photo attached:

Hi jcmb,

I found a AT to XT adapter that will solve the lack of the XT keyboard.
The first link is for Microchip PIC12F629, the original one.
The second link is for PIC12F675.

https://www.minuszerodegrees.net/at2xtkb/AT2X … onal%20info.htm
https://www.mattmillman.com/building-an-at2xt … rototype-board/

Note1 : The code is different for each of the uC.
Note2 : The hardware is the same, so you can use PIC12F629 or PIC12F675 without any change on the PCB.

I'm going to make 2 units myself and I hope it solves 100% the problem of the lack of a true XT keyboard...

Hey SDumas,

thank you, this looks like a descent and hazzle-free solution to the keyboard problem.

After fiddling with the PSU connections and testing the voltages beforehand I'm also happy to report that my board is alive as well.

The Oak VGA card does work in a 8-bit slot.

For XT keyboard replacement I went with the RPi pico variant from said GitHub project (had a pico at home anyways). It seems to work very well even with wireless USB keyboards.
Right now I didn't get any further than POST and some error message afterwards but at least ESC and CTRL-ALT-DEL is working perfectly. 😁

I'm going to investigate further the board's floppy controller capabilities (double density should work) and report back afterwards. I also ordered additional compatible EEPROMs for tinkering.

Best regards

jcmb wrote on 2024-06-09, 15:06:

Hey SDumas, […]
Show full quote

Hey SDumas,

thank you, this looks like a descent and hazzle-free solution to the keyboard problem.

After fiddling with the PSU connections and testing the voltages beforehand I'm also happy to report that my board is alive as well.

The Oak VGA card does work in a 8-bit slot.

For XT keyboard replacement I went with the RPi pico variant from said GitHub project (had a pico at home anyways). It seems to work very well even with wireless USB keyboards.
Right now I didn't get any further than POST and some error message afterwards but at least ESC and CTRL-ALT-DEL is working perfectly. 😁

I'm going to investigate further the board's floppy controller capabilities (double density should work) and report back afterwards. I also ordered additional compatible EEPROMs for tinkering.

Best regards

I realize now that you have the same error as I did on the boot screen (error 64)
But before that the RAM count stopped at 384K Bytes. I don't know if this is the correct behavior.
How was it in your motherboard ?
For now I will not be able to do any more tests.
When I can, I will have to look more closely at these problems...

I spent some time searching for data on this motherboard and found some information that might be useful:
This motherboard was used on Tandon PC model TM6004A also known as PCX20 (This to be confirmed...)

There are some jumpers that we don't know their function like JP1, JP3, JP4 and JP5.

What i can tell you is that header J9 is for the speaker, P2 is the connector for the internal FDD controller
and P3 is the parallel connector.
And pay attention that pin 1 of these 2 connectors are close to the power connector.

Hi SDumas,

I believe the error code is expected. The RAM check on my model runs every time on cold boot then completes and shows the error message. Maybe due lack of BASIC ROM (not integrated in the 16K EPROM as opposed to IBM 5160's 32K ROM) and/or boot drive. But at least a speaker connected to JP9 sounds a nice short beep on bootup. 😀

At first it only passed 128K since memory bank 3 was missing a parity chip. Starting from the leftmost bank the memory has to be coherent. Switched it over from bank 4 and now I got a juicy 192K!

As far as I can tell from the initial pictures your board's slotted chips are OKI M41256A. 8*32K each = 256K per bank 3 and 4 -> 512K.
The soldered amount is 128K the maximum is 640K. So I guess there's either something wrong with a component on bank 4 or some solder joint or jumper connection yet to be opened/closed. Maybe try reseating the RAM chips...

Bingo! Got the same results as you from my research! 😀
Yours is probably even a TM6005. Hence the "higher" board model (003) than mine (001), maxed out 640K "OKI" branded RAM and an 8Mhz Intel D8088-2.
See for example this gallery: https://www.facebook.com/groups/1859472814329 … 92058741070704/.
There are also a couple of German brochures on archive.org and eBay confirming your findings.

Some interesting news to me is that the Tandy 1200 is again a clone of the Tandon.
https://www.reddit.com/r/vintagecomputing/com … comment/dsppapq
https://youtu.be/oSDtnQMUBeQ?t=279

Given that is true it could become valuable info regarding this guy's findings on the weird floppy controller connector:
https://youtu.be/oSDtnQMUBeQ?t=171

I'm under the impression that the internet is now pretty much drained of information about the Tandon PC/PCX(xx)/XPC(xx). 😁
Concerning the jumper settings we might see if there's something useful to transfer over from the Tandy 1200 manuals. 😀

Thank you

SDumas wrote on 2024-06-09, 18:31:

I realize now that you have the same error as I did on the boot screen (error 64)
But before that the RAM count stopped at 384K Bytes. I don't know if this is the correct behavior.
How was it in your motherboard ?

Just compared your screenshot and mine and realized your JP1 wasn't set.
Out of curiosity I removed mine and now I also get a strange RAM check until 384K even though the system only has 256K.
Not a 100% sure about the background but try putting a jumper on JP1 and you should receive a whopping 640K with your current setup.