Now how to fix the various issues with this laptop:
Power Supply
The original AST part code for the PSU is 501250-001 and the model name is "ADP-LK", which looks to be available with Dell and Digital labels. It outputs 14v at 1.5 amps and the tip dimensions are 6.3mm outer diameter with 3.0mm inner diameter, or 6.3 x 3.0mm.
You can use a Toshiba 15v power supply with this like the PA2450U (15v @ 3a) which is much cheaper and easier to source, there is no risk to attaching a higher amperage PSU that I'm aware of - I regularly use mine with a USB Power Delivery adapter that tells the USB-C / USB-PD power supply to output 15 volts

Disassembling the Laptop
To get inside the laptop, first of all lift up the plastic strip above the F1 key where it says "Backlight On/Off", there is an M2.5x21mm screw hidden under there. Then unscrew the 2x M3x5mm screws on the underside of the front of the laptop which are hidden under the rubber feet at the corners, you can use a drawing pin to poke into and lever the rubber feet out without causing much damage to them.
Don't remove the covers / screws at the rear corners, they hold the screen in place.
Remove the battery by sliding the Battery Release slider at the back underside of the laptop, the battery should then pop out slightly. Once removed, unscrew the 4x M2.5x4mm screws in the battery tray area.
Flip the laptop over and open the screen all the way back, the top case can then be lifted off starting at the back, go slow because the top case is still attached at the front end. Once it's lifted up a little bit, undo the flex cable at the front for the keyboard and unhook the cable for the trackballm now the top case can be put aside.

Be careful moving the laptop at this point, the screen is no longer fully secured in place with its metal pegs that slot into the lower case, which need the top case to hold them in place properly.
You can remove the 4x M2.5x4mm screws holding the metal shield over the main chipset, but they don't need to be removed to replace the hard drive.
I found that the screw thread under the keyboard is broken and that can be fixed with hot glue / polymorph plastic / sugru.

Remove and/or Replace the Hard Drive
With the top case removed, remove the two M2.5x3mm screws highlighted for the hard drive in the above image. The hard drive in its sheath can now be rotated up and out of the way so that it can be unplugged from the 44-pin flex cable. Be careful with the flex cable as they can potentially rip. My method is to gently pry the connector at the hard drive end with the hard drive resting upside-down on top of the battery tray area.
To recover the contents of the hard drive, plug it into an old PC that supports CHS (Cylinder/Head/Sector) IDE drives as an intermediary - modern USB to IDE adapters will not be able to read the drive.
To replace the drive you would need to source a drive the same as the one that was removed - because the BIOS only supports a limited set of hard drives, like the Toshiba T1850's BIOS.

I was able to resolve this in finding that my mono AST Bravo NB 4/25s has BIOS 1.07 which supports auto detection of hard disks / Compact Flash cards under 504MB in size, I use it with an industrial 256MB CompactFlash in a 44-pin IDE adapter.
The hard drive hole locations are different from modern drives, I use a 3d printed adapter that I haven't released yet but the CF card could be put back into the sheath and hold in place nicely without a 3d printed adapter.
If you have an EEPROM programmer like the TL866 or xgecu T48, remove the BIOS flash chip - labelled "LK4B" in the below image, that's the LK4B BIOS chip, the other is LK4P which is the keyboard / embedded controller data.
Take a backup of the chip contents, then you could try the BIOS files in the attached zip file to update to 1.07 BIOS. Be aware that this will only work for the mono and colour DSTN variants of the AST Bravo NB 4/25 and may work with the 4/33 model. If you've got the ColorPlus / TFT variant these files won't work for your laptop, but send me a backup of that and I can help by stitching it together with 1.07 BIOS. I have searched extensively but have not found the AST Bravo NB BIOS 1.07 available anywhere online.

If you have a Digital / Dell or other brand then these bios files will likely not work. I tried Dell's Latitude 433C A07 BIOS on my AST Bravo NB and it didn't work. But there may be BIOS updates available for your brand of laptop, I suspect that Dell's A07 is the same as the AST's 1.07 BIOS.

Memory
These laptops have 4MB of memory built onto the motherboard, which can be expanded to either 8MB or 20MB. The memory modules are installed in pairs because each memory stick is 16-bits wide, a 486 requires a pair of them to operate because it has 32-bit wide memory in total. See the picture above for a good example of how the memory modules look and should be installed.
The memory modules are not vendor specific so modules for a Dell Latitude 433 will work with any of the laptops mentioned in the previous post.
Potentially now that PCBs are easier to manufacture, we could make up a replacement since the memory modules look like a simple 4-layer design. But it's not like these laptops are going to be running Duke Nukem 3D or Windows 98.

Floppy Drive
The floppy drive is a Mitsumi D353F2 which is belt driven. This is bad because the belts have all perished after this long - that drive can be replaced with either a direct-drive D353F3 or a Teac FD05HG since it's a standard pinout.
I have never succeeded in replacing the belt in a D353F2 drive - other manufacturers made their drives to be serviceable but this one isn't easily dismantled to replace the belt.
Modern direct-drive slim 26-pin floppy drives are cheap and easy to source.

PCMCIA
If your laptop is missing the PCMCIA cover or the PCMCIA slot protector, be aware that the PCMCIA cards must be inserted upside-down, which is just how it's designed.
The PCMCIA was apparently bootable in an early BIOS but that's disabled in the BIOS versions I have (1.03 & 1.07) - PCMCIA on this also seems to have a weird quirk in that it'll happily run a real PCMCIA ATA hard drive, but try a compact flash or SSD and the computer will freeze / hardlock. Haven't tried that with Windows 95 though.
Personally I've used Cardsoft 3.0 and probably Cardsoft for DOS 5.30.10 would work, though apparently the original hard drive install used Phoenix Card Manager

Capacitors
For a computer that's run long enough, capacitors can become a problem and you'll know there's a problem if you smell something like fried fish when the computer is running. Here are my experiences with replacing two capacitors in the main DC-to-DC circuit that runs the laptop: Re: What retro activity did you get up to today?
There are also capacitors in the LCD screen panel, you can tell if they're failing because on a DSTN screen you'd see lines all the way vertically on the screen following lines of things like a text box or window on the screen.

External Mouse or Keyboard not working
This may be unique to just my laptop but I found that it could not detect PS/2 mice when plugged in, the trackball is not much fun to use for long so I investigated and found that a connection that provided power to the external mouse was broken: Re: What retro activity did you get up to today?

RTC Battery / CMOS Battery
This is a rechargeable VL1220 (Vanadium Lithium, 12mm diameter, 2mm height) battery that is soldered to the mainboard, it charges when the laptop is powered and will fully discharge if the laptop is left unpowered for a while, maybe a month or so. Because the BIOS auto detects which hard drive is connected on startup either from a list of known drives or fully auto detecting, the RTC battery is not essential to keep charged at all times. You can power on the laptop after months and it should work without issue because of the auto detection, just need to reset the time.
This battery should only be changed if it completely fails to keep charged but isn't very important.
Please do not replace this battery with a non-rechargeable Lithium cell like a CR2032 coin cell, the laptop will be putting power into the cell while running and that is not safe with non-rechargeable lithium cells. Just replace with another VL1220

Nice laptops!

I have AST Advantage Explorer 486SX/25, works, but with vinegar syndrome screen 🙁

MAZter wrote on 2024-06-26, 18:57:

Nice laptops!

I have AST Advantage Explorer 486SX/25, works, but with vinegar syndrome screen 🙁

Ooh, I see it, the one at the end of this post right? Re: What is your oldest working Brand name computer ? - ( Challenge ).
So there's yet another one, the AST Advantage Explorer 486SX/25 - longest name yet? 😀 I invite anyone else that finds another name / rebrand to mention it here.

Regarding the vinegar syndrome / LCD polariser breakdown, that's something I've also experienced with my mono AST Bravo NB, I tried and failed to replace its polarisers since both the outer and inner polarisers started turning into vinegar / acetic acid. In removing the inner polariser at some point I damaged the middle of the LCD. The screen for that one is an LM64P83 which is soo expensive - I eventually found a 10.4" screen that could fit in its place, the LM64P89 - good as new!

See the last pictures on this post for the new screen fitment: Re: What retro activity did you get up to today?
My guess is that whatever Sharp used to make the mono LCD into a 'paperwhite' colour makes it less stable than other polariser materials

For anyone wondering, the "Color" model which is 640x480 DSTN colour uses a Sharp LM64C08P, my one had a big splotch in the middle and it was replaced with an LM64C081 which was a spare screen for a Compaq and looks great.

As the owner of 3 of them (all AST, one new and the other two second hand), great thread!

One thing that isn't great with those is the trackball, that's for sure, and without PS/2 ports on the back as it was the case for the Ascentia 700N/33 I have, it was used with a serial trackpad most of the time.

Interesting to know about the early bios pcmcia boot support, and I also confirm the pcmcia slot not accepting compact flash adapters without locking up or just refusing to power on.
Mine came with Cardsoft, not the Phoenix manager.
Along with Dos 6.21 and Windows 3.1 or 3.11

There is a vesa tsr around, I posted it some years ago, if you would need high res in Dos, for some reason.
I also have the box of the Ascentia 700N/33Mhz, I posted pictures in another thread but I can add them here another time.

Never knew about the external battery, it would have been useful back in the day.
I have the official car power supply adapter for it somewhere.

I see you solved the no soundcard problem with a Portable Sound Plus,I remember it working quite nice.
Another possibilty is a pcmcia soundcards leaving the parallel port for external storage.

Memory expansion on it is a must if you consider using Windows 95, Linux or NextStep for example, with only the onboad 4MB, you better keep it as a dos/win3x machine.

lolo799 wrote on 2024-06-28, 10:25:

Memory expansion on it is a must

So how to increase memory in this machine?

MAZter wrote on 2024-06-28, 17:18:

lolo799 wrote on 2024-06-28, 10:25:

Memory expansion on it is a must

So how to increase memory in this machine?

Look in Thermalwrong's second post, memory expansions were available for sale, either 2*2MB or 2*8MB sticks for a total of 8 or 20MB of RAM.

lolo799 wrote on 2024-06-28, 19:08:

Look in Thermalwrong's second post, memory expansions were available for sale, either 2*2MB or 2*8MB sticks for a total of 8 or 20MB of RAM.

Thanks, not sure if possible find them for sale.

My screen looks like this:

MAZter wrote on 2024-07-01, 01:17:

Thanks, not sure if possible find them for sale. […]
Show full quote

Thanks, not sure if possible find them for sale.

My screen looks like this:

2 of the 3 700N I have also have this screen issue, atleast you can still use the vga out.
I see you still have the ast disk utility on your hdd, save that somewhere else!

Pictures of the box I have:

You can see the problem developing in the middle of the screen, with some careful contrat settings it's legible, like now, but by default it's more visible:

This one is way worse, but the laptop doesn't boot further, keyboard error and I can't enter the setup screen...

lolo799 wrote on 2024-07-18, 11:14:

I see you still have the ast disk utility on your hdd, save that somewhere else!

I can upload some folders to Archive.org.

lolo799 wrote on 2024-07-18, 11:23:

You can see the problem developing in the middle of the screen, with some careful contrat settings it's legible, like now, but b […]
Show full quote

You can see the problem developing in the middle of the screen, with some careful contrat settings it's legible, like now, but by default it's more visible:

The attachment ast700n1.jpg is no longer available

This one is way worse, but the laptop doesn't boot further, keyboard error and I can't enter the setup screen...

The attachment ast700n2.jpg is no longer available

It does seem like every one of these monochrome laptops has a problem with the LCD at this point, where 'vinegar syndrome' or polariser breakdown of the front and/or rear polariser is making the screens unworkable.
I've been looking into polarisation for DSTN screens for a long long time now, my best attempts just resulted in weird colours and low contrast because there's something special about these monochrome & colour DSTN displays, that regular replacement polarisation sheets don't match up with - I made some progress the other day with the original 9.5" monochrome panel from my AST Bravo NB 4/25: Re: Vinegar syndrome and choosing new polarising film
In those pictures I've stripped off the bad polariser sheets and the secret ingredient seems to be sticky tape to get the proper monochrome colour profile back. Though I'm working on finding a better solution that won't leave little gaps all over the place.

If any of these laptops are going to survive long term, we're going to need to figure out how to fix these polarisers more easily and without damaging the LCD in the process.

If you want to fix your monochrome screen or DSTN colour screen, buy some of this stuff and hope you can get the bad polariser off without damaging it: https://vi.aliexpress.com/item/10050063575359 … ayAdapt=glo2vnm
That's the proper solution that will stick down to the LCD glass. It's pricey and the glue is a one-shot thing so you should get a shop to do it or practise on other screens first.

What you need is FSTN film: https://www.aliexpress.us/item/3256806171221164.html
It has an extra "retarder" layer which is what fixes the incorrect colors.

aaaand that's what you had linked to. whoops.

3lectr1c wrote on 2024-10-10, 14:27:

What you need is FSTN film: https://www.aliexpress.us/item/3256806171221164.html
It has an extra "retarder" layer which is what fixes the incorrect colors.

aaaand that's what you had linked to. whoops.

Kinda, check out where I've now got to with some 25 micron (1 mil / 100 gauge) polypropylene film:

That line is because I don't have one complete regular polariser sheet without glue that fits this screen.

BTW do you know if 68kmla is a functioning website / forum? I'm trying to sign up on there but can't get the verification email and the 'contact us' form also fails 😒

That's a pretty decent looking result - get rid of the line and it would be perfect.

68kMLA is functional, the problem is the main administrator has clearly lost motivation to work on the site, so when a problem occurs, it can take a while for it to be fixed.... email delivery broke earlier this week. I'd hope it will be fixed in another week, but yes, it's a pain.