Hi, I know that this post is a year old, and sorry for reviving it, but I want to share the method I used to add the 3,3v CPU support, and don't want to create a new post because this one is very complete.
I think is itresting to undevolt the CPU, in my case the 486DX4 100MHz is stable at 2,62v and very very cold.
I know it's not period correct but it's a lot more eficient and gives a voltage very stable compared to the linear voltage regulators, and the XL4005 doesn't get hot at all.

Huh. That's one interesting method.

This method can be used on any 486 motherboard that doesn't have the 3.3v voltage regulator components and should be plenty powerful for any socket 3 compatible processor. It will surely have its problems but I haven't run into any yet.

Good afternoon, I have an idea to create an open source project for a 146380-Packard Bell PB45F30P expansion PCB. To do this, of course, you need the board itself for its reverse engineering, but you can try to recreate it from a photo in high resolution and from different angles. If anyone wants to help, please post a photo.

noid@engineer.com

I have a Packard Bell 450 MB with a VGA video issue, there is vertical banding on the image only when playing games, dos and win 3.11 look fine. I installed an ISA VGA card and the issue is resoled but I want to use the on board VGA as I have installed the 1mb video upgrade to 2mb. Is it possible that the issue is caused by bad caps? if so does someone have a list of caps to replace in the video section I can try? The mainboard is a PC 4401-03 with Cirrus DG5428.

Here is a photo of the vertical lines.

Hoping wrote on 2022-05-03, 15:14:

Hi, I know that this post is a year old, and sorry for reviving it, but I want to share the method I used to add the 3,3v CPU support, and don't want to create a new post because this one is very complete.
I think is itresting to undevolt the CPU, in my case the 486DX4 100MHz is stable at 2,62v and very very cold.
I know it's not period correct but it's a lot more eficient and gives a voltage very stable compared to the linear voltage regulators, and the XL4005 doesn't get hot at all.

Wires might be too thin for the distance VRM is from the CPU

I used that connector and wires because I had then at hand, maybe not the best, next time I'm thinking on using a biger connector an thicker wires, thanks for the tip.

Hello all. I was going through this thread and I've done much of the same without soldering things (just yet) and for whatever reason I cannot get the PCI video card to come up.

Onboard works, but discrete does not. I've changed the vgae jumper on the board and just get a black screen. I know this computer is pushing it's age, but I'm not sure where to start.

It's a Packard Bell Executive 466 (Which uses the 450 motherboard), with a 486DX2-66 processor.

Hey Packard Bell enjoyers. Got a mystery for you guys.

I recently performed the full gamut of upgrades on my Legend 204CD with the PB450 motherboard. My system is now voltage modded (image attached) using a method similar to Hoping's method posted above: Re: Packard bell PB450 repair / mods / upgrade. I have also added 512K of cache, 32MB RAM, the Micro Firmware BIOS, etc.

I put in an AMD 5x86-133 ADW, and have had mostly positive results. Except for one strange issue. A small number of programs will cause the keyboard to reset constantly, about twice per second (LEDs flashing). So far this is most noticeable in Descent: If you get into the game and then pause with Esc, while on the "Quit Game" prompt the LEDs will flash. This makes it very difficult to get back out of the menu since the keyboard responds poorly. In addition, sometimes in-game the keys will get "stuck" in the down position or the game will lock up. The only two other places I have observed this so far is the Blood setup program (and only when doing the sound effects test), and the installer for XCOM: UFO Defense (keyboard LEDs flashing during disk copy). It's mostly been a nuisance up to this point but now I've also run into some minor file system corruption across multiple disks now, which is suspicious.

I performed the following tests/swaps to rule things out:

• removed all cards
• memory test
• cache test + tested with cache removed
• power supply swap to a modern ATX w/ adapter
• slightly increased voltage to the 5x86 to 3.5v
• switched FSB from 33mhz to 25mhz

That basically left the voltage mod as suspect, so I bypassed the mod and tried the original DX2-66 @ 5v with Descent since it shows the most obvious issues. No problems. Then to test the voltage mod, I tried running it at 3.3V (which it works fine at)... also no problems. Hmmm. So I pulled out as many 486's as I could find in storage and tested them all with interesting results.

• Intel 486DX2-66 (original CPU for this system, not sure of S-Spec due to glued on heatsink) - no problems
• AMD Am486DX4-100 (SV8B, 25544 package code) - problems
• AMD Am486DX4-120 (SV8B, 25398 package code, running at 100mhz since this board doesn't do 40mhz FSB) - no problems
• AMD Am5x86-133 ADW (25544 package code) - problems
• IBM/Cyrix 5x86C-100HF - no problems

So the issue is seemingly limited to AMD CPUs based on the 5x86, which use the 25544 package code. The big difference between those and the DX4-120 that does work is that the 25544s are a later 350nm package with 16KB L1 according to the info here. The thing is, though, that plenty of people have run 5x86s on this board, both through voltage mods and standard upgrade kits with regulators, and I've seen no mention of problems. I even checked Usenet archives to see if anyone reported anything back in the day. What exactly is going on here?

I'm using the IBM 5x86C for now since it seems to be the fastest CPU that isn't presenting issues, but I would love to know what in particular is different about the AMD 5x86 that is causing it to act up. If anyone has more CPUs to test maybe we can see if my findings are a coincidence, or localized to my specific machine.

Also a side mystery, can anyone help me figure out what VRAM I need to do the VRAM upgrade? Per the manual, it wants "two 256x16 (70ns) DRAM ZIP chips with (2) CAS lines (symmetrical)". I bought some NEC chips I thought would be compatible (NEC D424170V-70), but when installed the system then only detects 512K of VRAM instead of the default 1MB or the upgraded 2MB. Very strange. I'm guessing they don't fit the "symmetrical CAS lines" requirement since it seems oddly specific, but I couldn't find enough info to tell. I am fairly sure the chips are not defective, as I have 10 of them and I find it hard to believe that all 10 would be bad.

Sorry to revive an old thread, but looking online for information on upgrading this machine is getting difficult as time goes on.

I have unearthed my Multimedia Executive as it was called in thr UK which has is a PB450M based system, 30 years old and it still works after living in the loft/attic all this time.

I have done a few basic mods like adding a CF adapter so I can backup the hard drive and make data transfer easier.

I have now purchased am5x86 133 and also ordered the bits needed to add to the motherboard to make it work.

I realise now that there will hardly be any performance gains without L2 cache. I can't find these chips anywhere, digikey says they are now obsolete with no option to buy.

Am I out of luck? I'm starting to spend a little too much time and money on this possibly, but I want to keep this old machine going before it inevitably goes back in the loft/attic again for another decade or so.

MDave wrote on 2025-04-12, 23:44:

Sorry to revive an old thread, but looking online for information on upgrading this machine is getting difficult as time goes on […]
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Sorry to revive an old thread, but looking online for information on upgrading this machine is getting difficult as time goes on.

I have unearthed my Multimedia Executive as it was called in thr UK which has is a PB450M based system, 30 years old and it still works after living in the loft/attic all this time.

I have done a few basic mods like adding a CF adapter so I can backup the hard drive and make data transfer easier.

I have now purchased am5x86 133 and also ordered the bits needed to add to the motherboard to make it work.

I realise now that there will hardly be any performance gains without L2 cache. I can't find these chips anywhere, digikey says they are now obsolete with no option to buy.

Am I out of luck? I'm starting to spend a little too much time and money on this possibly, but I want to keep this old machine going before it inevitably goes back in the loft/attic again for another decade or so.

I am not sure what availability is in the UK,

for the 128K configuration, the manual calls for: five 32Kx8 and one 64Kx1
for the 512K configuration, four 128Kx8, one 32Kx8, and one 64Kx1.

You can use all 15ns parts even though the board tolerates 20ns for data SRAM.

32Kx8 is still manufactured, or was recently. US Mouser p/n AS7C256C-15PCN
128Kx8 has new old stock on ebay, p/n IS61C1024-15N. You need a chip tester such as TL-866 II or its successor as there are bad ones mixed in.
64Kx1 (22-pin) fell into obscurity sooner. I don't see any on ebay that is fast enough. I haven't seen one of these boards since 2005; it's possible it will work without it as "always dirty" with slightly lower performance until you find another solution or modify the board to take something else. edit: CY7C187-15PC on ebay

Thank you! I bought the 512k configuration from all UK sellers on Ebay, I did not know you could mix and match different sizes for the 4 cache slots as long as they totalled up to what you needed. I'll find out in about a week how it goes. Much appreciated! ... wife will kill me if she knew what I'm doing haha.

djgeojoe wrote on 2022-06-09, 10:55:

Here is a photo of the vertical lines.

The attachment Screenshot_20220607-202218_Gallery.jpg is no longer available

I sort of fixed this issue with my old Dell 19 inch VGA input only LCD monitor, in the monitor OSD settings turn down the phase clock from the default 50 to 0. You get an absolutely noise free/vertical line free image and it looks fantastic but you get thin black bars on the sides. It's worth it though. Other monitors probably give different results.

I realise I made some errors in what I posted above;

I wrote messages too early after waking up haha, I am mistaken thinking you can mix and match different size memory caches for the 4 cache slots. I see 32Kx8 cache chips could be used for both cache and the TAG slot for the 128KB?

This is what I bought:

I was also mistaken about the term for fixing the image quality issue, it was Pixel Clock set to 0 and then adjust the Horizontal Position to 100. DOS and DOS games that play in the 320 x 200 don't play well with these old LCD monitors as they pick up the signal in mine as 720 x 400 @70Hz which give the vertical bars.

It's not that you can "mix and match" but that you need to use what the board was wired for, and when it was designed, 64Kx8 and 128Kx8 either wasn't available in 15ns or was too expensive, thus this motley assortment of chips needed, vs. a typical no name 486 board that would simply take nine 32Kx8 chips for 256KB cache + tag (and then either write-through, 7+1 tag, or always dirty)

Thank you for the detailed information, it is appreciated. My board is this one http://www.uktsupport.co.uk/pb/mb/450.htm with a 486DX2-66, 12MB ram.

Question, is it worthwhile performing the bios flash to Micro firmware bios now so I that side of things is prepped while I wait for the parts?

I've also got a 5x86, regulator bits and a set of cache chips ready to go into my Packard bell. just got the regulator this weekend.

Ebay seller is offering a CY7C187-25PC instead of the CY7C187-15PC as that is all they have in stock at the moment. I don't think that will work? If I go without this chip I only get a dirty cache message on boot?

All the parts except for the CPU, Cache TAG and Cache DB have arrived, so I got to soldering.

System boots okay afterwards.

Those tantalun capacitors were very tricky to keep in place while soldering them to the board, but got there in the end.

Next is flashing the bios.