Restoring some Toshiba 486 & Pentium Laptops

Aug 25, 2021 | Computing

As with some of my other projects, these machines came from the vintage tech sale in Q1 2020 just before the first lockdown. The sale was absolutely massive ( a few photos below ) and there were bins upon bins of laptops, which at the time had been a big attraction for me as you can play around with different setups without taking up too much space. I did a quick boot test and one of them booted up with Windows 3.11 and the others didn’t power up at all. I did end up going back the next day and getting the other T4700CS for parts, so I ended up with 4 in total:

  • 2x T4900CT, Pentium 75 machine
  • T4850CT, 486-DX4 machine
  • T4700CS, 486-DX2 machine

Diagnosis

Breaking down the machines, one of the T4900CT worked out of the box, just had a bad hard drive and a dead battery. The T4850 did not power on at all, it turns out that it was some of the capacitors on the power supply module, which once swapped it worked perfectly well. The T4700CS worked but the screen had dead pixels all through it and the other T4900CT didn’t work, but when I swapped the motherboards it has had a screen with a dead pixels.

This left me with a working T4850CT, a working T4900CT and a working T4700CS with a bad screen.

Donor parts hunting

I did some hunting slowly online and spotted a T4850CT with on eBay with $15USD in somewhat good condition. I ordered it and got it drop shipped here via NZPost. Trick for the future, they do not ship devices with NiMH batteries in there. Once it arrived, I attempted to boot it up and was greeted with a dead machine, not unexpected for its ages. As the T4700 and the T4850CT share the same platform I I swapped over the working motherboard from the 4700 and it kicked into life, and it even had a good screen and power supply! So I ended up with a T4850CT with a DX2 not a DX4, not the end of the world. I swapped over the best parts of each unit and put them both together. Turns out two of the machines had ram expanders as well so I put them in the T4900 and the T4850.

This left me with 3 working units, two totally dead units. I sold off the dead ones on trademe in case someone needed parts from them. All in all a good restoration so far from a big of laptops at a random sale. Two slight things I still need to look into is that the floppy drives don’t seem to read disks, but that is for another day and the the DX2 4850 needs a new CMOS battery.

 

Loading up DOS Images

I loaded up my usual DOS image that I made and it all works perfectly. One thing to note on these machines is they will not see any drive over 2GB, this is a bios limit NOT a Dos 6.22 limit. I have dropped some screenshots of what is included in my DOS image if anyone is curious.

Specifications

Below is some of the specs of the machines but the general rundown is:\

  • T4900CT, Pentium 75mhz, 24MB of ram ( inc expansion card ), 2GB DOS 6.22 CF card, 1.44MB 3.5″ floppy, 10.4″ TFT Color Display 640×480,
  • Vesa Local-bus video adapter, C&T F65545, Analog Devices AD1848KP & Yamaha OPL3
  • T4850CT, 486-DX4 75mhz, 24MB of ram ( inc expansion card ), 2GB DOS 6.22 CF card, 1.44MB 3.5″ floppy, 10.4″ TFT Color Display 640×480, WD90C24A2 video chip, Analog Devices AD1848KP & Yamaha OPL3
  • T4850CT, 486-DX2 50mhz, 8MB of ram ( inc expansion card ), 2GB DOS 6.22 CF card, 1.44MB 3.5″ floppy,10.4″ TFT Color Display 640×480, WD90C24A2 video chip, Analog Devices AD1848KP & Yamaha OPL3

Performance

Some interesting results benchmarking running the system information tool in Phils Computer Lab pack. The disk speed on the T4900 was higher even though they all had the same CF to IDE adapters in them. The CPU speeds, well the Pentium clearly was faster at 237.6 but the DX4 and DX2 were the same at 73 which shows the test doesn’t make much difference on a DX4. The over tests also seem to reflect this as well.

The final working units

Overall, a cool project and I ended up with some fun machines to play with. Just need to figure out how to get those damn floppy drives working.

  • T4900CT, Pentium 75mhz, 24MB of ram
  • T4850CT, 486-DX4 75mhz, 24MB of ram
  • T4850CT, 486-DX2 50mhz, 8MB of ram

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