I also removed the 24/h battery and it didn't solve the problem.

.

/teary eyes
Its beautiful!

Theretroweb doesnt have this one. I would love a good picture of whole mobo front and back and a BIOS dump 😀 closest one is this https://theretroweb.com/motherboards/s/zenith … s-zds-z-486-25e and its evidently Very different (EISA, Intel chipset, no video).

Yours has some lovely quirks like that Video memory on custom 20pin SIPPs 😮

Good news - I disassembled BIOS of 386 model https://github.com/raszpl/Zenith_ZBIOS and know more than I ever wanted about it.

Bad news - Zenith was very advanced, they didnt play placebo games. On most ZDS systems Password is truly secure and managed by a "System Control Processor" (beefed up Keyboard controller ) like in modern Laptops. What are the markings on U47 chip (close to power connector)?

Someone ran into the same issue on a Z-LS/20 BIOS Password on Zenith Z-LS/20
I couldn't figure out where the password was stored. I think it's some issue where, when the original battery dies, there is no direct way to get back to the factory config with an empty password.
However, in that thread, you can see I figured out how to permanently bypass the password check by flashing a new BIOS chip with a trivial patch. It's likely a similar approach can be taken on yours. But it does require a hardware fix.

This may be the ICU ( ISA Configuration Utility) mentioned in the attached text, so maybe worth a shot... Re: Zenith Data Systems Z-400+

Setup […]
Show full quote

Setup

The Z-400+ systems use ISA Configuration Utility. It is a software based
configuration program that is pre-installed onto the hard drive and is
backed up on a floppy diskette.The ICU allows the user to set:
system security, password security, (supervisor and user), video,
floppy, hard drive, I/O ports and boot options, as well as the standard
setup configurations previously offered in all of the Zenith Data Systems
computers.

Flash BIOS
BIOS which is incorporated in the Z-400+ is stored in erasable and
reprogrammable Intel Flash memory. By incorporating the experience learned
in the laptop arena, ZDS extends the useful life of each system and
provides an upgrade path that is both convenient and fast. All Z-400+
users can upgrade their BIOS by simply installing it onto their systems
from a floppy diskette. No replacement of circuits or ROM chipsis
necessary.

Security

The Z-400+ systems have dual password protection featuring Supervisor
level security that will only permit hardware configuration unlock after
supervisor identification has been confirmed.

Security Features

Dual Password Protection Supervisor and User passwords

Floppy and Hard Drive - Disables any access to
Enable/Disable floppy and hard drives

Floppy write protect Disallows floppy writes to the
floppy (through dip switches)

Serial and Parallel port Prevents access to
- Enable/Disable Serial and Parallel port

Server Mode No-prompt password:Allows system,
acting as a server,to boot through
execution without a password message
being seen.

ROM Debugger disable Disallows ROM debugger access
through a dip switches.

Locking mechanism Optional Security loop/Cover lock

jakethompson1 wrote on 2026-08-10, 23:16:

I couldn't figure out where the password was stored.

Serial eeprom wired directly to "System Control Processor" aka KBC. I see three candidates on Zenith Z-LS/20. U51 but that might just be an LM393 generating powergood, U69 (nice) stuck in the opposite corner of the board, or most likely U42 right next to Signetics PLA Im guessing is hosting custom KBC.

jakethompson1 wrote on 2026-08-10, 23:16:

I think it's some issue where, when the original battery dies, there is no direct way to get back to the factory config with an empty password.

Hmm what do you mean? Afaik CMOS contents&battery status is in no way linked to password status. Resetting CMOS with inactive passwords will not somehow set a password. Am I wrong?

jakethompson1 wrote on 2026-08-10, 23:16:

However, in that thread, you can see I figured out how to permanently bypass the password check by flashing a new BIOS chip with a trivial patch.

Nice. I havent see confirmation by ajacocks that it worked. Did you test it on real hardware? There is possibility Zenith made KBC not respond to anything until Password is entered and validated.

PC Hoarder Patrol wrote on 2026-08-10, 23:54:

This may be the ICU ( ISA Configuration Utility) mentioned in the attached text, so maybe worth a shot... Re: Zenith Data Systems Z-400+

You wont be able to run anything with password enabled. That thread has fantastic picture of another sexy Zenith Z-425/SX owned by esver Re: Zenith Data Systems Z-400+
On that model Password sits inside U106 in lower right corner between KBC and Keyboard connector. Still just because we know which chips is the magic EEPROM with password doesnt mean we would be able to remove the password. If we are lucky and Zenith did something stupid merely erasing EEPROM would suffice, maybe give us this
' ERROR: Old password invalid, password cleared, Press RETURN to continue ',0
but imo its more likely that will result in
' ERROR: Cannot program Password Chip, ESC to continue ',0
with ECS leading to reset loop

rasz_pl wrote on 2026-08-11, 00:03:

jakethompson1 wrote on 2026-08-10, 23:16:

However, in that thread, you can see I figured out how to permanently bypass the password check by flashing a new BIOS chip with a trivial patch.

Nice. I havent see confirmation by ajacocks that it worked. Did you test it on real hardware? There is possibility Zenith made KBC not respond to anything until Password is entered and validated.

I checked PMs and I don't see it either. But I know him in real life so maybe we only talked about it there?

I also thought of Need Help with Quadtel BIOS for My Emerson 500EC... and the patch did work on real hardware there.

rasz_pl wrote on 2026-08-11, 00:03:

jakethompson1 wrote on 2026-08-10, 23:16:

I think it's some issue where, when the original battery dies, there is no direct way to get back to the factory config with an empty password.

Hmm what do you mean? Afaik CMOS contents&battery status is in no way linked to password status. Resetting CMOS with inactive passwords will not somehow set a password. Am I wrong?

I agree it would not.
I was assuming that the issue with these machines was that they did not have a password set, and suddenly gained one. If that is true, then either the EEPROM gets corrupt, or my hypothesis was, there is some flag in the CMOS that gets reset after the battery dies indicating there is a password hash in EEPROM, and it doesn't hash to anything valid.

But that could be completely wrong. Maybe the previous owner did set a password.
I just talked to ajacocks; apparently that machine failed before the modified BIOS could be tested. So it was indeed the Emerson I was thinking of where the mod actually worked.

Zenith were trying to impress government and medical markets with that malarkey I think.

It is possible that this system has a Packard Bell twin without this password feature and that BIOS might work.

Though whenever you try a battery pull to zap a password, yet still get the password prompt always check if it's an empty string (press return) or a simple default admin or something.

jakethompson1 wrote on 2026-08-11, 00:15:

I checked PMs and I don't see it either. But I know him in real life so maybe we only talked about it there?

Would be great to get confirmation.

jakethompson1 wrote on 2026-08-11, 00:15:

I also thought of Need Help with Quadtel BIOS for My Emerson 500EC... and the patch did work on real hardware there.

Does Emerson send same commands to KBC as Zenith? do they share KBC sauce somehow?

jakethompson1 wrote on 2026-08-11, 00:23:

my hypothesis was, there is some flag in the CMOS that gets reset after the battery dies indicating there is a password hash in EEPROM, and it doesn't hash to anything valid.

here is how it chcks if password is set: https://github.com/raszpl/Zenith_ZBIOS/blob/a … 3.2C.lst#L32497

The way I understand it It first queries KBC to check if it likes this KBC at all, then if the password is supported, then if password is enabled, and only THEN it will check if CMOS has enabled Password. Cleared RTC CMOS combined with Password set will trigger https://github.com/raszpl/Zenith_ZBIOS/blob/a … 3.2C.lst#L21446
'--- Errors found! Please press <Esc> to continue ---',0
with optional
'--- Errors found! Please unlock keyboard, then press <Esc> to continue ---',0
Now that I looked at it again it does strongly suggests KBC is not locked up before entering password since this error message wants user to press Esc ... unless Zenith was clever and KBC only passes Esc scancode before validating password 😀

jakethompson1 wrote on 2026-08-11, 00:15:

I just talked to ajacocks; apparently that machine failed before the modified BIOS could be tested.

🙁((((

BitWrangler wrote on 2026-08-11, 00:56:

Zenith were trying to impress government and medical markets with that malarkey I think.

and engineers considering build-in Debugger inside BIOS 😀

BitWrangler wrote on 2026-08-11, 00:56:

It is possible that this system has a Packard Bell twin without this password feature and that BIOS might work.

Packard Bell, and what a dumpster fire and a scam city central that company was, happened in 1996.

https://dfarq.homeip.net/happened-packard-bell/ :
"“I don’t know about other brands,” one customer said to me when I was selling computers in 1994, pointing at Compaq and Dell. “But Packard Bell, that’s an old company.” Even my coworkers routinely thought Packard Bell was related to HP or to Packard, the car maker."

rasz_pl wrote on 2026-08-11, 01:02:

Packard Bell, and what a dumpster fire and a scam city central that company was, happened in 1996.

That's when PB bought out Zenith, prior to that, Zenith/Bull had near 20% of PB and they were collaborating on some models.

Try the grounding trick from here: Re: BIOS password bypass on Zenith Data Systems Z-Note 325L?

This is soo upsetting ... to me 😀 So much for me hyping up Zenith if all it takes is removing socketed EEPROM 😐
Good news for fearangel if he uploads better pictures and we can locate eeprom.

rasz_pl wrote on 2026-08-10, 22:30:

/teary eyes Its beautiful! […]
Show full quote

/teary eyes
Its beautiful!

Theretroweb doesnt have this one. I would love a good picture of whole mobo front and back and a BIOS dump 😀 closest one is this https://theretroweb.com/motherboards/s/zenith … s-zds-z-486-25e and its evidently Very different (EISA, Intel chipset, no video).

Yours has some lovely quirks like that Video memory on custom 20pin SIPPs 😮

Good news - I disassembled BIOS of 386 model https://github.com/raszpl/Zenith_ZBIOS and know more than I ever wanted about it.

Bad news - Zenith was very advanced, they didnt play placebo games. On most ZDS systems Password is truly secure and managed by a "System Control Processor" (beefed up Keyboard controller ) like in modern Laptops. What are the markings on U47 chip (close to power connector)?

Hi, yes I take pictures of the motherboard and then send them to be posted on RetroWeb (as soon as I disassemble everything to clean it).

I'm busy with my work, but I can take better photos later.
Thank you for your help!