Zenith MinisPort laptop memory issue?

[Paul Rickards]

Hi All,

I'm restoring a Zenith MinisPort laptop, an 8088 based laptop with a
monochrome screen and 2" floppy drive.

I have a Twitter thread of the restoration so far with pics:
https://twitter.com/paulrickards/status/1272280795529519105

I recapped the internal power supply board which seems to be working well
now.

The next issue appears to be memory. The unit won't store the BIOS settings
properly, even with new lithium batteries or warm restart. In the BIOS
menu, setting the clock with a "0" changes to "32". Same with the date, if
you set the day or month, it adds 32 to it.

The internal memory test reported a memory error at B800:0000 bit 5. This
seems to coincide with the BIOS "0" turning into 32 on screen.

When it eventually boots from the internal MS-DOS 3.3 ROM, it looks fine
until the screen starts to scroll. The character case of all text on the
screen changes from lower to upper case.

Anyone know how to map a bit 5 error to a component on the motherboard?
Would a memory map help here?

Longshot: anyone have a service manual for the Zenith MinisPort ZL-1 (or
ZL-2)?

Thanks,
Paul Rickards
biosrhythm.com