Went with dual 1N5408 now, which output 4.2V in idle and fit nicely after removing the heatsink and reattaching it with superglue.
Runs absolutely stable with 24.1fps in Quake_low making it the fastest sub-Socket4 machine of the German DOS community 😀 There's still some room for improvement, as the POD only runs in WT mode on my current board.
Diodes get quite warm, but nothing overly worrying.

Glad to hear it is working out for you. I've done this mode with the double diodes without removing the heatsink, but requires more delicacy.

Very few motherboards work properly with the POD in WB mode, but they do exist however rare.

My POD has been running absolutely rock solid at 100Mhz, thanks to the info in this thread.

Has anyone had any luck with posting at a bus speed setting of 50Mhz?

Would there be a way to get something in between 40-50Mhz , to try and push the speed just a bit higher?

Chadti99 wrote on 2021-01-30, 18:44:

Would there be a way to get something in between 40-50Mhz , to try and push the speed just a bit higher?

Yes, a few have modded the pcchips m571 for 100mhz FSB by tweaking the source on the clock generator

Same could be done to the pll on a 486 or if you have an older board just replace the clock crystal

I think I've seen a few people POST their POD's at 125 MHz (2.5x50), however I don't think any were long-term stable.

Replacing the clock crystal doesn't always work as it messes up the timing of other systems, most notable will be the the floppy controller not working properly.

Thanks guys, always looking for a way to push this system a little bit more.

It was suggested i share these two clean implementations of the final mod design:

This one turned even better:

Full story and details here.

Yes, thank you. A gorgeous mod esp. with the Intel heatsink installed. Were you able to do the mod without removing the re-gluing the heatsink? I found it is just doable without removing the heatsink.

feipoa wrote on 2021-01-31, 00:25:

Replacing the clock crystal doesn't always work as it messes up the timing of other systems, most notable will be the the floppy controller not working properly.

Disable onboard floppy controller, run an ISA floppy card problem solved

rmay635703 wrote on 2021-03-07, 00:39:

feipoa wrote on 2021-01-31, 00:25:

Replacing the clock crystal doesn't always work as it messes up the timing of other systems, most notable will be the the floppy controller not working properly.

Disable onboard floppy controller, run an ISA floppy card problem solved

It's not very elegant though. But if you are OK with this type of solution, then more power to ya. So what FSB are you using now and is everything else running fine?

Thanks.

The first cpu was modded long ago.
Primary objective was to make it work, looks were secondary.
I will probably redo it for pretty at some point.
Its heatsink has opening at the front which allows to make the mod without removing it.
Currently I use this one because of the better ventilation.
The big fan is noisier, but keeps long term stability in check, especially inside closed case.
The computer is fully equiped and maxed out, so it gets warm inside.

The second modded cpu turned even better.
This time "looks" were in the front seat.
This heatsink model has a grill on top of the elements.
Had to use thin and long soldering hotend, inserted from the inner side to reach the back leg.

Ok here is my attempt on this:
https://youtu.be/JVpmTlndEco

A lot of information in this video. I think I cover everything.
Half of the video is about modifying the cooling and the voltage regulator.
The rest is Overclocking / Underclocking records.

It will be interesting to see if any others are willing to run their POD off their motherboard's VRM or using an externally connected VRM, and if so, can stable 125 MHz be achieved.

All the modification attempts are too risky, why don't you simple move to a Pentium III with a good AGP graphics card and go like that? Even an Intel i740 or an on board i815 graphics have Windows 3.1 drivers if needed. For engineers, the way taken from year from 1995 to 2000 is astonishing. ISA --> EISA --> VL-Bus --> PCI --> AGP.... (1x, 2x, 4x, 8x)

A Pentium Overdrive processor for 486 systems have many limitations. First of all, the memory speed is around 25 MB/s for Fast Page memory, 40 MB/s for EDO. A 133 MHz Pentium III with a SD-Ram gives you around +220 MB/s. From the point of graphics card, at most those 486 systems have 512 kb to maximum 2 MB graphics card. (There were 4 MB ones for example from Matrox but impossible to find.) The ram speed causes bus speed limitation. All ISA slots all together the "total" bandwidth is 16 Megabytes/second for 16 bit bus. So if you have a disk controller normally 2 to 4 MB/s transfer speed it can need. A sound card takes 1 or 2 megabytes bandwidth. A basic ethernet card 10 Mbps, around 150 kB, A graphics card can take at most 8~10 MB from that sharing. Remaining bandwidth goes to other components such as floppy, serial, printer ports etc. You can not hope much from a 10 MB/s graphics bus paired with a really limited processing power. This means overclocking a CPU can not change the result much. On an EISA bus 32 bit by 8,33 MHz gives 33 MB/s total bandwidth. But, the majority of this generally goes to SCSI bus on them, around 10 MB/s. The ram speed of Fast page memory's 25 MB/s does not help going more over that, so EISA bus can give at most 25 MB/s actual use. Early PCI buses also can not give actual 133 MB/s speed, because of the same Ram speed limitation. If there is a double channel Socket 7 Pentium with EDO, it can try at most 40 x 2 = 80 MB/s for the all bus bandwidth use, but here early Pentium processing speed is not enough, it can not calculate that much, starting from +200 MHz Pentium MMX and Pentium Pro can barely go up to this limit. Do not forget, theoretical PCI bus transfer speed is 133 MB/s for all PCI busses, not for each! Actual speed for all slots are around 60 to 80 MB/s. I have tested this with a PCI Raid card with 8 units of 250 GB IDE drives with Raid 0 configuration many years ago.

If you want to play Doom faster try Nintendo version "Doom 64 for PC" is much better, but still not very fine. It has very high system resources like GeForce 6xx card, 8 GB Ram, AMD Athlon FX or Intel 2nd gen processor and so on. So you don't need to have an early 486 or Pentium for it.

Playing over a transistor with diodes: Well a transistor is a twin diode nevertheless. If you want to increase Voltage, you have to replace the 3.3 Volt, 3 pin regulating transistor, to a one step stronger 3.45 Volt one! All other attepts are actually not engineering. Just replace Voltage regulator chip. The AT power supply, (generally) the well known double 6 pin, or 8 pin connector, has it's limits. On more powerful mainboards, for example on Compaq systems there is another 3rd 6 pin power cable. But, 5 Volt processor supply is an old one, today we are using the processor power from 12 Volt rail with a additional 4 or 8 pin, 8 + 4 pin, or 8 + 8 pin and so on.

I have a Compaq ProSignia 486 mainboard with a Pentium overdrive. I have replaced 16 MHz oscillator to 17.35 MHz one. My 83 MHz Pentium Overdrive runs at 90 MHz. The ram performance increased a bit around 27 MB/s because the oscillator replacement increased 8,33 MHz bus to 9 MHz. I have thought about replacing the oscillator to 19.2 MHz to achieve 10 MHz EISA bus and likewise 100 MHz for my Pentium Overdrive, but decided not to force that much. The overdrive chip perhaps may need 3,3 to 3.45 Volt regulator replacement, but I have an Intel 815 chipset based Pentium III 1 GHz mainboard with onboard graphics, an Asus P3C-E mainboard with Pentium III 600E and 1400 MHz Tualatin processor. So, why do I have to? I have plenty of ram on them and a nVidia 6800 based 256 MB AGP graphics card. I have one AGP based Matrox G550 and an AGP based Intel 740 graphics card as well. Those systems have much faster disk speed compared to a 486 or early Pentium mainboard.

So, if you have such old systems, try not to modify them too hard, a bit is fine. We have many newer systems, if you need plenty of more speed try your way by changing to an upper platform....

I am adding a fixed Voltage regulator chip that outputs 3.45 Volt. There are many other types as well. Those can give maximum of 1,5 Amperes, there is no higher Amp capable one, as far as I know. So you have to stay within the limits, or the chip dies! http://pdf.datasheet.directory/datasheets-1/s … ch/EZ1086CM.pdf

The benefit is: (3.45 Volt x 1.5 Ampere = 5.175 Watt) - (3.3 Volt x 1.5 Ampere = 4.95) = 0.255 Watt only! I can not found LT912CM datasheet anywhere, so I am only assuming it is 1.5 Ampere. All regulator chips generally goes upto 1.5 Ampere including metal ones, small ones, well known 78xx series etc. if Intel's part is different, I can not guarantee the maths I did! Note: Please be aware that, this part's input is 5 Volt, some 3.6 Volt output capable ones need 18 Volts like LT1086CM-3.6

Attention latest note: (LT1585-3.6) is {4.80V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 4A}, terribly 4 Ampere capable! The LT912CM Intel chip might be a maximum (LT1585-3.3) {4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 4.6A} 4.6 Ampere! modders can use this one! 😀 Maybe it can be stronger as well.... https://www.analog.com/media/en/technical-doc … ets/158457a.pdf

Nodded in agreement to every point you made ... in principle.
Unfortunately most Vogoners do not attend meetings of the National assembly for rational thinking and common sense.
: )

Joking aside, i know what you mean, but this chain of thought leads directly to software emulation running on present day hardware.
A great option for getting our dose of nostalgia, but for many here journey is the mission itself and here comes the old computer hardware.
It usually starts with "i am just going to make a replica of my first computer" only to find yourself ourselves years later on an irrational path of obscure retro computing activities.
Modding being one of them.

pshipkov wrote on 2023-02-19, 03:54:

...but for many here journey is the mission itself and here comes the old computer hardware.
It usually starts with "i am just going to make a replica of my first computer" only to find yourself ourselves years later on an irrational path of obscure retro computing activities.
Modding being one of them.

That pretty much sums it up. My recommendation - get out while you still can.

pshipkov and feipoa,
I know those of course, I was hoping those replies, I have used the old stuff the 1990's PC is my time. I am 52 years of age. But, the things I have written down are true. I wish I have a better option in 1995 for example. 😀 I have waited too long for todays stuff. That time was a terrible time for finding the parts, wondering around. You can not shop by internet for computer parts. The known brands such as Asus was not famous before 1995, their mainboards were terrible we were calling them needle station. IDE, Floppy connectors does not have plastic bases under them etc. The things were not fine, you can have the knowledge and options today. But, at that time, people are buying their first computers by sight only. "I like this one, how much?" was a common computer question....

karakarga wrote on 2023-02-18, 23:55:

All the modification attempts are too risky, why don't you simple move to a Pentium III with a good AGP graphics card and go lik […]
Show full quote

All the modification attempts are too risky, why don't you simple move to a Pentium III with a good AGP graphics card and go like that? Even an Intel i740 or an on board i815 graphics have Windows 3.1 drivers if needed. For engineers, the way taken from year from 1995 to 2000 is astonishing. ISA --> EISA --> VL-Bus --> PCI --> AGP.... (1x, 2x, 4x, 8x)

A Pentium Overdrive processor for 486 systems have many limitations. First of all, the memory speed is around 25 MB/s for Fast Page memory, 40 MB/s for EDO. A 133 MHz Pentium III with a SD-Ram gives you around +220 MB/s. From the point of graphics card, at most those 486 systems have 512 kb to maximum 2 MB graphics card. (There were 4 MB ones for example from Matrox but impossible to find.) The ram speed causes bus speed limitation. All ISA slots all together the "total" bandwidth is 16 Megabytes/second for 16 bit bus. So if you have a disk controller normally 2 to 4 MB/s transfer speed it can need. A sound card takes 1 or 2 megabytes bandwidth. A basic ethernet card 10 Mbps, around 150 kB, A graphics card can take at most 8~10 MB from that sharing. Remaining bandwidth goes to other components such as floppy, serial, printer ports etc. You can not hope much from a 10 MB/s graphics bus paired with a really limited processing power. This means overclocking a CPU can not change the result much. On an EISA bus 32 bit by 8,33 MHz gives 33 MB/s total bandwidth. But, the majority of this generally goes to SCSI bus on them, around 10 MB/s. The ram speed of Fast page memory's 25 MB/s does not help going more over that, so EISA bus can give at most 25 MB/s actual use. Early PCI buses also can not give actual 133 MB/s speed, because of the same Ram speed limitation. If there is a double channel Socket 7 Pentium with EDO, it can try at most 40 x 2 = 80 MB/s for the all bus bandwidth use, but here early Pentium processing speed is not enough, it can not calculate that much, starting from +200 MHz Pentium MMX and Pentium Pro can barely go up to this limit. Do not forget, theoretical PCI bus transfer speed is 133 MB/s for all PCI busses, not for each! Actual speed for all slots are around 60 to 80 MB/s. I have tested this with a PCI Raid card with 8 units of 250 GB IDE drives with Raid 0 configuration many years ago.

If you want to play Doom faster try Nintendo version "Doom 64 for PC" is much better, but still not very fine. It has very high system resources like GeForce 6xx card, 8 GB Ram, AMD Athlon FX or Intel 2nd gen processor and so on. So you don't need to have an early 486 or Pentium for it.

Playing over a transistor with diodes: Well a transistor is a twin diode nevertheless. If you want to increase Voltage, you have to replace the 3.3 Volt, 3 pin regulating transistor, to a one step stronger 3.45 Volt one! All other attepts are actually not engineering. Just replace Voltage regulator chip. The AT power supply, (generally) the well known double 6 pin, or 8 pin connector, has it's limits. On more powerful mainboards, for example on Compaq systems there is another 3rd 6 pin power cable. But, 5 Volt processor supply is an old one, today we are using the processor power from 12 Volt rail with a additional 4 or 8 pin, 8 + 4 pin, or 8 + 8 pin and so on.

I have a Compaq ProSignia 486 mainboard with a Pentium overdrive. I have replaced 16 MHz oscillator to 17.35 MHz one. My 83 MHz Pentium Overdrive runs at 90 MHz. The ram performance increased a bit around 27 MB/s because the oscillator replacement increased 8,33 MHz bus to 9 MHz. I have thought about replacing the oscillator to 19.2 MHz to achieve 10 MHz EISA bus and likewise 100 MHz for my Pentium Overdrive, but decided not to force that much. The overdrive chip perhaps may need 3,3 to 3.45 Volt regulator replacement, but I have an Intel 815 chipset based Pentium III 1 GHz mainboard with onboard graphics, an Asus P3C-E mainboard with Pentium III 600E and 1400 MHz Tualatin processor. So, why do I have to? I have plenty of ram on them and a nVidia 6800 based 256 MB AGP graphics card. I have one AGP based Matrox G550 and an AGP based Intel 740 graphics card as well. Those systems have much faster disk speed compared to a 486 or early Pentium mainboard.

So, if you have such old systems, try not to modify them too hard, a bit is fine. We have many newer systems, if you need plenty of more speed try your way by changing to an upper platform....

I am adding a fixed Voltage regulator chip that outputs 3.45 Volt. There are many other types as well. Those can give maximum of 1,5 Amperes, there is no higher Amp capable one, as far as I know. So you have to stay within the limits, or the chip dies! http://pdf.datasheet.directory/datasheets-1/s … ch/EZ1086CM.pdf

The benefit is: (3.45 Volt x 1.5 Ampere = 5.175 Watt) - (3.3 Volt x 1.5 Ampere = 4.95) = 0.255 Watt only! I can not found LT912CM datasheet anywhere, so I am only assuming it is 1.5 Ampere. All regulator chips generally goes upto 1.5 Ampere including metal ones, small ones, well known 78xx series etc. if Intel's part is different, I can not guarantee the maths I did!

Hello,

I stopped reading after:
"
All the modification attempts are too risky, why don't you simple move to a Pentium III with a good AGP graphics card and go like that?
...
"
It's like telling a collector of old cars: Why don't you buy a new car, it is faster and needs fewer repairs.

CoffeeOne wrote on 2023-02-19, 11:59:

It's like telling a collector of old cars: Why don't you buy a new car, it is faster and needs fewer repairs.

I have a fairly full proof rationale for that argument - where I live, if your car is at least 25 years old and in good condition, you can apply for Collector plates. This reduces your auto insurance and registration fees by about 85%.

@karakarga
Most here share your stance.
This is main motivational factor for me personally.
To play with the old toys i never had and find which ones were the coolest.

@feipoa
Should we propose a similar bill for retro computers, so i can write-off taxes or something because of this 286 hot-rod in the back room.