HP Vectra VE 5/133 Series 3, help with understanding VRM module resistors, Pentium MMX upgrade \ VOGONS

HP Vectra VE 5/133 Series 3, help with understanding VRM module resistors, Pentium MMX upgrade

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First post, by cristy6100

Posted on 2023-01-10, 22:27

cristy6100 Offline

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Joined: 2023-01-10, 22:07

Hello and a good day, after many years I finally got the time to get this bad boy up and running, was a new old stock PC, first boot since it was made, still with 12MB RAM, 256KB cache module, still new Quantum 1.2GB HDD, Pentium 133Mhz, gradually I will start to clean it and make it a retro Windows 95 machine for some nice throwbacks to the good old days.
I am familiar with most hardware from this era growing with it, but I totally skipped the whole Pentium/MMX generation instead I upgraded straight from 486 to Pentium II back then, so I am a bit unfamiliar with how and why HP wired 2 resistors in the VRM socket, and as to why is there no VRM header on this motherboard? As far as I remember it used to be either the MB had a onboard VRM to convert 5V to 3.3V, or as HP and other OEM's they had 3.3V directly from the PSU with a 6Pin header 3Pins for GND and 3 pins for 3.3V, now the problem is I want to upgrade the CPU to something faster, like a 200MHz MMX or 233Mhz MMX, these ones need 2.8V if I remember right and we used to plug a VRM module in the header, and here is where I am a bit at a loss, I can build a VRM module to convert 3.3V to 2.8V but I don't understand why are there 2 resistors in that header?
Searching on the forums it seems there are multiple revisions of this PC and motherboard, some with a header, some without.
It seems the resistors bridge 5V pin to VSS pin, and I don't understand why is this necessary? Having the 3.3V header from the PSU, what is the need for those 2 resistors?
Is it safe to remove them and add a VRM module for 2.8V?

I wish a good day to all of you and I appreciate all time and help with this

Christan

Reply 1 of 2, by cristy6100

Posted on 2023-01-12, 02:34

cristy6100 Offline

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Joined: 2023-01-10, 22:07

I managed to up the CPU from 133MHz to 200MHz by looking at the VL5 manual and adjusting for 3X multi, officially the VE5 only goes up to 166MHz in the manual, I am still confused about the 200 MMX upgrade, is it worth it, will be installing Windows 98/Me on this machine maybe tops Windows 2000 for fun
Thanks

Reply 2 of 2, by dionb

Posted on 2023-01-12, 12:21

dionb Offline

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cristy6100 wrote on 2023-01-12, 02:34:

I managed to up the CPU from 133MHz to 200MHz by looking at the VL5 manual and adjusting for 3X multi, officially the VE5 only goes up to 166MHz in the manual, I am still confused about the 200 MMX upgrade, is it worth it, will be installing Windows 98/Me on this machine maybe tops Windows 2000 for fun
Thanks

The MMX instructions are pretty pointless, a few winmodems aside, nothing that would run on a 200MHz system sensibly uses them. But the P55C design doubled L1 cache and that improves performance. Also with 2.8V you could install a P233MMX (or OC the P200MMX to 233MHz) which will improve performance further.

But... it's still a P1-class system with a slow old SiS 5511 chipset and VGA with UMA (that SiS 6205 shares memory bandwidth with CPU) so whatever you do this system will be a slug. If you want a faster system, get a faster system. With current CPU and RAM you could get >25% increase with a decent i430TX-based system, and any Slot 1 system would blow it out of the water. Win2k would run on this (heck, XP would) but it would be no fun, no games and few other applications that prefer Win2k over 9x or DOS would run acceptably. Also with those OS you hit the cachable RAM limits.

If on the other hand you want the challenge to max this system out, a P233MMX would improve performance almost as much. De-solder the resistors, solder in a VRM header (good luck finding one of those...) then add the VRM and you should be good.

However there's an easier way to boost performance by up to 50% in things that use both CPU and VGA at the same time (i.e. games): add a PCI VGA card and disable (or at least stop using) the onboard UMA VGA.

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