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Texas Instruments 650CD: Testing Desktop CPU Upgrades on a Laptop

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First post, by Retroinside

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Hi everyone,
I recently tried something unusual with a Texas Instruments 650CD laptop, originally equipped with a Pentium 133. Since it used a standard desktop CPU, I decided to experiment with a few upgrades using CPUs I had that run at 3.52V (as specified).

Specifically, I tested:

  • IDT Winchip C6
  • AMD K5 Pr133
  • IDT Winchip2

The experiment had several limits:

  • The voltage is capped at 3.52V.
  • The FSB frequency is fixed, although I can switch it between 60 MHz and 66 MHz using two DIP switches.
  • The CPU multiplier is fixed at 2×, so any CPU—like the Winchip C6 or Winchip2—will always run at 133 MHz, even if it’s originally a 200 MHz part.

My main goal was to see if the laptop could even boot with such unconventional CPUs, and whether I could somehow get a performance improvement thanks to the efficiency of the different architectures.

If, on top of that, I managed to get the Winchip2 working stably, with performance exceeding the original Pentium at 133 MHz and with MMX and 3D Now! support… well, that would be an absolute triumph!

The CPU swap process was straightforward, but the results were definitely unexpected.

Check out the video here:
https://youtu.be/lWnwaK1SHn0

Has anyone else tried unusual CPU upgrades on old laptops? I’d love to hear your experiences!

Reply 1 of 2, by BitWrangler

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Video only seemed to go up to the C6.

But anyway, looked like what I would expect. Really the Winchips are only an upgrade when you are extremely limited by power budget and also can get them running at high frequency. Otherwise you need like 150% to equal the intel. Anyway, it's possible that board has a hidden jumper or jumper pads to set to 1.5x which may produce a higher multiplier on a Winchip 2.. they seem to be all over the place Winchip BF pin mappings. I think you are okay for power with a Winchip until ~233Mhz.

If there is just no jumper, pads or solder bridge, nothing, then you can "socket trick" the BF pins with small loops of wire to peg the BF pins high or low to adjacent VCC or GND to produce desired multiplier, or tie the pins on the chip with figure eights of fine wire around them.

The Win95 problem should be solvable. When you know what CPU you're keeping in, if it's not back to the P133 then just boot into safe mode and reboot, if that doesn't fix it, then may need reinstall.

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.

Reply 2 of 2, by Retroinside

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BitWrangler wrote on 2025-09-01, 13:07:
Video only seemed to go up to the C6. […]
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Video only seemed to go up to the C6.

But anyway, looked like what I would expect. Really the Winchips are only an upgrade when you are extremely limited by power budget and also can get them running at high frequency. Otherwise you need like 150% to equal the intel. Anyway, it's possible that board has a hidden jumper or jumper pads to set to 1.5x which may produce a higher multiplier on a Winchip 2.. they seem to be all over the place Winchip BF pin mappings. I think you are okay for power with a Winchip until ~233Mhz.

If there is just no jumper, pads or solder bridge, nothing, then you can "socket trick" the BF pins with small loops of wire to peg the BF pins high or low to adjacent VCC or GND to produce desired multiplier, or tie the pins on the chip with figure eights of fine wire around them.

The Win95 problem should be solvable. When you know what CPU you're keeping in, if it's not back to the P133 then just boot into safe mode and reboot, if that doesn't fix it, then may need reinstall.

Hi there, and thanks so much for your super helpful response!
I was also hoping for some jumpers to set the multiplier, and you’ll get a laugh out of this; I actually pulled the motherboard out of the notebook to check!
Unfortunately, there’s nothing. Only on the power board are there some switches, which most likely manage the voltage. But since there’s no written reference, I don’t feel comfortable touching those settings.
Regarding the Winchip, you’re absolutely right.
I totally agree with you. I got my hopes up with the Winchip2 (which I received the very same day of testing it in the notebook), and not knowing it well, after seeing the PC boot, I was hoping it would be a big hit.
Such a pity. If one day I manage to get my hands on a Cyrix 6x86 at 3.52V, I’d really like to see how it performs.
Thanks also for the Windows 95 tip, i honestly hadn’t thought about that workaround anymore.

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