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Zenith MinisPort HD - Hard Disk solution

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silence012

Experienced Member
Joined
Oct 21, 2020
Messages
101
Location
Austria
Hi all,

I am restoring a Zenith MinisPort HD (version with HDD) but unfortunately HDD is gone. Interestingly enough, it is not possible to run MS-DOS from ROM unless you have a working HDD.

I do have an external FDD, and after some errors I can book MS-DOS from it.

I tried putting CF2IDE adapter but it seems does not work. Tried to set CHS parameters on CF hard to match original HDD (Conner CP-2024) but it didn't work. Not sure if BIOS has any drive name limitations (like in case of most vintage Toshiba laptops) or I am doing something wrong.

Does anyone have any experience with it? Anything useful to share?

BIOS ROM is Atmel AT27C512R (PLCC version).

I do have an adapter for dumping it, but as it is soldered on PCB I am kind of afraid that I can damage it. If anyone has a dump of bios ROM, please let me know. I can try to inspect it and see if there is any specific limitation when it comes to HDD and also the reason why one cannot start ROM based DOS without HDD.
In mean time, I'll try to export BIOS content using DEBUG command from DOS. Hopefully it will work.

I appreciate any kind of help to make this machine up and running. Really nice piece of computer history.

Branko
 
How big of CF Card are you using? I found I had better luck with industrial cards and especially ones under 1 gb. I installed a IDE to CF into an AST Advantage NB and the bios vlaims to not see it but it still works.
 
The hard drive can be saved if the goo that seals the enclosure didn't get onto the platter. Most likely the rubber head stop turned to goo and you can try to open it in a dust free environment to free it up. It can be covered with something like capton tape to prevent the head from sticking to it

Edit, maybe check here:
 
Unfortuntately, in this case it cannot be recovered. I already fixed few drives with the same trick but here the motor is dead.
Anyway, it would be nice to find some kind of long term solution like CF2IDE.
 
Hm that is bad then. Interestingly, the drive is still working without problems in the one I've got.

The BIOS only accepts type 1 hard disks, but maybe you can hack it. I dumped it with DUMPPC for you (remove the .txt from the file ending).

I hope you replaced the electrolytics in the PSU, they leak quite badly (including the notorious series of Nichicons that leak)
 

Attachments

@Vintage Computer Club CH indeed, there was lot of leakage on the PSU board. I also had a burned 2SK612 but it is all sorted now. All voltages are ok, although brightness does not change intensity. I check a pot and it seem OK, so could be something on PSU side. Will look into it a little bit later. Another problem is that number "9" on keyboard does not work. Ironically, with NUM LOCK, number 9 is also on the same key, so currently I don't have a way how to type number 9. Will look into at as well.

Thanks a lot for ROM dump. As it is 256K, do you know where is it mapped in memory space? BIOS ROM AT27C512R is 512K, so I guess not all memory is used, has to check if there is an unused address line.
 
Just checked a board. Apparently PIN 2 on chip (which is address line A15) is not used, which means computer is using only 256K of ROM. Wasting half of the capacity :)
 
I don't know the BIOS version, if I find some old pictures from when I restored mine I can try to check it. The MFM-180 monitor program is 3.4B

My LCD backlight came back when I completely recapped the PSU, but I also made sure all is clean and that no trace was broken
 
I managed to find a BIOS from the file you've sent me. It is basically only 64K out of these 256K. The first 196K looks like charset for graphics. Trying to debug it together with my friend chatGPT and so far I haven't found any limitation in terms of HDD naming.

LCD backlight works for me, but only with one intensity. If you move pot, nothing is changed. Contrast works as expected.

Does your laptop works right now? Do you have working setup?
 
After full day of debugging bios ROM, found few places where HDD is checked during the initialization process. The problem is that there is no easy way to check what exactly fails when I use CF2IDE.

Here is an example:

b8 01 12 MOV AX,0x1201
b9 01 00 MOV CX,0x1
cd 13 INT 0x13
72 f3 JC LAB_f000_5023
b8 01 14 MOV AX,0x1401
cd 13 INT 0x13
72 ec JC LAB_f000_5023
c7 06 6c MOV word ptr [offset DAT_0000_046c],0x0
00 00 00
81 3e 72 CMP word ptr [offset DAT_0000_0472],0x1234
00 34 12
75 06 JNZ LAB_f000_504b
c7 06 6c MOV word ptr [offset DAT_0000_046c],0x18c
00 8c 01

With HDD in place, everything works as expected.

I should get tomorrow an SD2IDE card and will give it a try.

@Vintage Computer Club CH the ROM you provided is a little bit different than mine. So there are some versioning in place.
 
You probably have to try different adapters and/or CF cards, this was always a lottery for me. I currently don't have one available to try but I couldn't set any other hard disk type other than the one it has CHS 612/4/17
 
@Vintage Computer Club CH Do you currently use CF or regular HDD?

I found few things today.

The computer itself seems do not have a HDD controller, but instead it relays on CP-2024 integrated controller. This means that it will be probably very hard (if possible at all) to make it work with CF2IDE adapter.

I also found, that after all errors, if you wait long enough (~5min) it will boot from ROM even if there is no HDD attached which is very good. If I don't find some working solution I'll live it that way.

With SD2IDE adapter it has a similar error. So I don't think it will work.

I am not an expert in this area, so if anyone has more info please write it here to keep it as a future reference.
 
@Vintage Computer Club CH thanks for the hint.

Apparently none of my CF cards work for this laptop. I decided to park it for now, turned off HDD in BIOS and boot from FDD. That combination works fine for now. I might revisit this in future.

From BIOS perspective, it seems that 2x3V batteries hold settings (and probably RAM drive) but not the clock. Looks like clock gets power from the main battery. That's weird :)

Is there any specific software that I put in it?
 
I read about the Conner CP-2024. It seems that it also supports XT mode. Since this is an XT clone computer, it could be that the HDD runs in XT mode so none of the CF cards will work unless the signals are translated somehow.

If you don't fix your main battery there is no point in putting in the 3V batteries. They are expensive and will deplete very quickly without the main battery holding the settings.

Don't know what software you want to run with it. Mine was heavily customised by the previous owner and came with word processing, terminal software (to use with the modem) and some simple CGA games
 
I am not planning to run any specific software on it, I enjoy more restauration than really paying with it later on :)

How did you open the battery to replace the cells? I guess it requires some cutting plastic?
 
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