Mine is the one labeled "235 of 304", with 236 being the image. Nothing there or in the "processor type" setting shows a bus speed toggle.

On that note, I've come across this listing. Would this allow me to use an Am5x86-P75 chip, or would the bus speed prevent that?

If the photo is in the manual the jumper settings are there.
168-pin CPU runs at 33mhz ( 5-volts )
169-pin CPU runs at 25mhz. ( 5-volts)
168-pin Intel Overdrive CPU’s require a setting of 33mhz. ( 5-volts )

Gnoman wrote on 2021-07-15, 23:49:

Mine is the one labeled "235 of 304", with 236 being the image. Nothing there or in the "processor type" setting shows a bus speed toggle.

On that note, I've come across this listing. Would this allow me to use an Am5x86-P75 chip, or would the bus speed prevent that?

Intel486dx33 is like this sometimes 😁. As far as I can tell, as everyone else has posted these boards are hard-wired for a specific clock rate. You may be able to change it but it might involve a soldering iron not just jumpers (unless there are undocumented ones).

Are you sure about not having the 169th hole. It would be on one of the interior corners of the socket--like one extra hole that looks out of place. If you do the math for all the others that are together (17*3*4 - 9*4 for the duplicate-counted corners) you get 168, making the out-of-place hole #169.

You can use the voltage adapter and a 5x86. The 5x86 will run at 100 MHz rather than 133 due to the 25 MHz clock. And the further away you get from the processors that existed when this board was designed, you more you risk a timing loop or something in the BIOS that isn't compatible anymore.

Short of actually popping out the CPU (which I am reluctant to do without a replacement, because of the risk of damage), I'm sure. Both the motherboard diagram and photos presented lack the single interior hole.

If you plan on sticking with Intel get the DX4- 100 overdrive appropriate for your system

It will easily run at 75mhz and you can easily swap the crystal for 100mhz operations at a later time should you choose to take it on

Gnoman wrote on 2021-07-15, 23:49:

Mine is the one labeled "235 of 304", with 236 being the image. Nothing there or in the "processor type" setting shows a bus speed toggle.

On that note, I've come across this listing. Would this allow me to use an Am5x86-P75 chip, or would the bus speed prevent that?

Yeah, I would buy it and put an Intel 486dx4-100 in it.
Then you could leave your current jumper settings alone.
All you have to do is swap CPU’s.

I am not sure what CPU’s this works with but it is written on back of this adapter.

486DX4-100s are clock tripled but 100 sounds better than 99....😉

Depends what your oscillator actually is though, I've seen both 33 even and 33.333 or 66 and 66.67 of course if you're s smerterse you look out for a 36 or a 68 🤣

Edit: BTW if you want to know the exact value to stick in a model 55 16Mhz SX that won't trip the overclock lockout in IBMs BIOS, it's 18.7 woohoo, speed demon, aholes wouldn't even let me have 20.

i had the same problem as you some months ago, were i posted photos of the motherboard and testing with a multimeter

Super expensive Pentium overdrive , any alternative?

and i had no luck finding a solution with the unknown jumpers and unsoldered jumper points in the board.

i do have :
-one dell voltage regulator socket with an LT1587 (no jumpers in it).
-one no brand voltage regulator socket with no signs of jumpers in it
- one DX4ODPR100 cpu

but i never tested those 3, the ps1 i bought was not cheap, kind of worried i could break something, so i left it at 50mhz

I've got an interposer and 5x86 (w/heatsink) on the way. Probably be in this thread again next month when they get here, either for help or to announce results.

Don't be surprised if you can't get the 4x multiplier going with the 5x86 installed. For whatever reason it seems to be an occasional issue with OEM BIOSes.
If your board is really from 1993, I would steer clear of the POD upgrades. Even boards from 94 and 95 can struggle with those.

You should try to determine the source of the clock signal on your board. Does it come from an oscillator or a clock generator?
I suspect the clock signal can be changed with minimal soldering. 33MHZ bus should actually give you a pretty noticeable speed boost, but if you have 25ns SRAM you'd definitely want to replace that too.

If I had to guess, I'd say that IC sitting next to the crystal is likely the clock generator. If you can read the model number on it, you might be able to figure out what the pins do, and it's possible that you can change the speed of your board by either removing or adding a 0 ohm resistor. If a 33MHz version of your board exists, you can probably figure out what to do just by comparing these two locations.

Like I stated previously. You really need a Pentium class CPU if you want a good DOS gaming computer that will
NOT hesitate or stutter in DOS game play.
And if you plan on running WIn95 on this computer you really need a Pentium class CPU too.
The 486 and 5x86 will struggle to play MP3’s and Video.
And may Stutter playing DOS games.

Thats why I said the only cost to performance upgrade is to move on to a Pentium Class CPU from a 486.
Otherwise you are just waisting your time and money.

Also with a Socket 7 motherboard you get better Performance RAM, Faster Video, Faster Motherboard BUS, PCI slots, and 32bit IDE Data transfers. I would go with an Intel 430VX or TX chipset motherboard and Pentium 75mhz to 200mhz MMX CPU.

Got the parts in today, went in mostly smoothly except for removal of the old chip - bent a few pins, and stuck some of the pins into my hand. Probably nothing permanent.

System POSTS without errors, Win95 detects it as an AMD CPU, and limited testing shows apparent performance increases in Duke3D and Win95. Need to do more testing, but it seems to be a total success.

The 5x86 133mhz can hardly play MP3’s and Video.
You really need a Pentium 75mhz at least for good DOS game play performance.

1. Why would I care about MP3 and Video on a retrogame box. That's not what this build is for.
2. Most DOS games predate the Pentium and play perfectly without one. Only a gibbering idiot would think that one is required.

Your "advice" is nonsensical, absurd, and completely wrong. Please stop inflicting it on me. I have ignored you every other time, and will continue to do so.

Gnoman wrote on 2021-07-23, 00:04:

1. Why would I care about MP3 and Video on a retrogame box. That's not what this build is for.
2. Most DOS games predate the Pentium and play perfectly without one. Only a gibbering idiot would think that one is required.

Your "advice" is nonsensical, absurd, and completely wrong. Please stop inflicting it on me. I have ignored you every other time, and will continue to do so.

Good on ya mate.

I Am just trying to save you some grief and money.

Watch this comparison video:
https://youtu.be/jISmJG8QK0A

I thought the whole point of the 5x86-133 was that it was about equal to the P75, except in floating point...I don't get the idea he wants to do CAD or play Quake, so his current upgrade should be plenty fast.

Out of curiosity, What does the bios recognize the AMD CPU as ?

Intel486dx33 wrote on 2021-07-23, 02:45:

Out of curiosity, What does the bios recognize the AMD CPU as ?

It may take a long time for him to get the chip.

The 66mhz version of the system and 50mhz version both had the same bios so hopefully IBM at least had dx4-100 support and it should see that.

IBM was known for dirty tricks so he should run a couple simple benchmarks to see what happens, unfortunate there isn’t a 3rd party bios upgrade for that machine