I'd have to take a look, but if I recall 5 K-ohm is way too small for this motherboard's voltage regulation circuit. I think they were using in the hundreds of K-ohms for their voltage divider, while most boards would use in thousands of ohms range. The value of the trimmer changes depending on if you are replacing R16 with a trimmer or putting the trimmer in parallel with R16. Whatever the value of R16 is would be one of your limits, the 4 V one. Depending on the circuit, the other limit (towards the 0 V end), would either be infinity (e.g. 10 M-ohm) or 0-ohms. I'd have to check. Read through this pdf, Modifying your motherboard's voltage regulator for overclocking

Thanks guys!

I shouldn't reply but let Feipoa clarify because iu didn't actually do this mod myself.

So today i was able to run 3x60 with cache timings 2-1-2, DRAM SPEED = FASTEST with 16Mb module.
+0.1 fps in Quake 1 (20.5), so it is possible. But system is not fully stable.
Same mem stick can do 200mhz at 212, but still unable to complete q1 reliably.
The search for good memory goes on - that is the current limitation.

Chadti99, looking at my notes for the LSD board, I have:

R16 if replaced with:
27 K-ohm = 3.45 V
30 K-ohm = 3.68 V
31 K-ohm = 3.75 V
36 K-ohm = 4.0 V

Since 3.45 V - 4.0 V is the target range, you'd want to replace R16 with a 50 k-ohm trim pot. This one should do: https://www.digikey.ca/en/products/detail/bou … -503RLF/2535946 But be warned, there is no suitable means to secure this trim-pot. If you solder the through-hole leads onto the surface mount pads, the continued torque of turning the screw or any small bang of the trim-pot could eventually rip up the SMD pad.

With my Biostar UUD mod, although the trim pot is soldered to the SMD pads, I have used JB Weld to secure the side of the trim pot to the shroud on the SIMM socket.

In most cases, depending on the regular used, a standard LDO (0.7 V drop) would mean you could go as high as 4.2 or 4.3 V. If they used a very low drop-out regulator, (0.3 V drop) then you might get to as high as 4.7 V. I've not seen any socket 3 boards use a very low drop-out regulator though. So most likely, with a 50K or 100K trim pot, you'd have a 3-4.2 V adjustment range. If the CPU draws too much current when overclocking, the upper limit of that 4.2 V range will shrink. For example, if you push an IBM 5x86c-100HF to 133 MHz, the max voltage gets closer to 3.85 V.

So far, best price I can find LP61256GS-8 for is $2.0 each. Anyone find better?

I bought from Kynix.
Chadti99 bought from 5here too I believe.
What is your source ?

pshipkov wrote on 2022-01-03, 05:17:

I shouldn't reply but let Feipoa clarify because iu didn't actually do this mod myself. […]
Show full quote

I shouldn't reply but let Feipoa clarify because iu didn't actually do this mod myself.

So today i was able to run 3x60 with cache timings 2-1-2, DRAM SPEED = FASTEST with 16Mb module.
+0.1 fps in Quake 1 (20.5), so it is possible. But system is not fully stable.
Same mem stick can do 200mhz at 212, but still unable to complete q1 reliably.
The search for good memory goes on - that is the current limitation.

Are you stable at 212 Fastest at 200Mhz(50x4)? I can def boot into Windows and run GLQuake etc for as long as I dare, so I might be close. 200MHz(66x3) eventually causes issues even at 313 Fastest with my current setup. Would probably help if I spread this thermal paste more evenly, the stuff I have is rather thick in viscosity. And monitor temps.

feipoa wrote on 2022-01-03, 08:07:

Chadti99, looking at my notes for the LSD board, I have: […]
Show full quote

Chadti99, looking at my notes for the LSD board, I have:

R16 if replaced with:
27 K-ohm = 3.45 V
30 K-ohm = 3.68 V
31 K-ohm = 3.75 V
36 K-ohm = 4.0 V

Since 3.45 V - 4.0 V is the target range, you'd want to replace R16 with a 50 k-ohm trim pot. This one should do: https://www.digikey.ca/en/products/detail/bou … -503RLF/2535946 But be warned, there is no suitable means to secure this trim-pot. If you solder the through-hole leads onto the surface mount pads, the continued torque of turning the screw or any small bang of the trim-pot could eventually rip up the SMD pad.

With my Biostar UUD mod, although the trim pot is soldered to the SMD pads, I have used JB Weld to secure the side of the trim pot to the shroud on the SIMM socket.

In most cases, depending on the regular used, a standard LDO (0.7 V drop) would mean you could go as high as 4.2 or 4.3 V. If they used a very low drop-out regulator, (0.3 V drop) then you might get to as high as 4.7 V. I've not seen any socket 3 boards use a very low drop-out regulator though. So most likely, with a 50K or 100K trim pot, you'd have a 3-4.2 V adjustment range. If the CPU draws too much current when overclocking, the upper limit of that 4.2 V range will shrink. For example, if you push an IBM 5x86c-100HF to 133 MHz, the max voltage gets closer to 3.85 V.

Thank you for this thorough explanation, ordering the part now. Just maybe if I can dial the CPU and Peltier voltage in just right I'll have something running at 200MHz without condensation. Wish I had a Cyrix chip to play with, still on the hunt.

200MHz (4x50) is stable with the tightest timings. Still, performance is lower than 3x66 with 3-1-2/3 and DRAM SPEED = FASTER.
Never checked thoroughly the 3x66 option other than some vertical tests. Will try that soon. Thinking to attempt to move that 180MHz PC to 200MHz. Will see how it goes.

pshipkov wrote on 2022-01-03, 15:29:

What is your source ?

Some place called Shenzhen Ruist Electronic Technology. www.szruist.com . I just placed my first order with them for about a dozen different items, probably 200 pieces total. We'll see...

What do you guys think about something like this for running adjustable voltage to a 12715 peltier? Ideally I’d like a way to do it from the ATX psu molex it’s already running on with the host system. That might require something custom. Wanting to try slightly lower voltages than the 5v I’m running it at now. Maybe 3-4.

Kungber DC Power Supply Variable, 30V 10A Adjustable Switching Regulated DC Bench Linear Power Supply with 4-Digits LED Power Display 5V2A USB Output, Coarse and Fine Adjustments with Alligator Leads https://www.amazon.com/dp/B08DJ1FDXV/ref=cm_s … ding=UTF8&psc=1

Probably any variable DC voltage supply would due. I ran my peltier off mine.

Hornet Technology VL-300 - one more VLB multi-io controller with full set of interfaces - SCSI/IDE/FDC/COM/LPT.
Based on Adaptec AIC-6360L for SCSI, Adaptec AIC-25VL01Q for IDE and UMC chip for the COM, LPT, joystick, etc.

Plugged the card into that fast Asus VLI PC, but the system/PSU immediately shutdown at power-up.
Tinkered a bit with the controller. Looked for visible damage, etc. Came out clean. The device is crisp through and through.
Decided to try it in another motherboard. Used latest revision PC-Chips M919i.
Power-up and the most lower-right capacitor blew-up spectacularly - fireworks, smoke and everything.
Immediately turned off power.
Did i damage the mobo ?
Removed the controller and turned it back on - all good. Sigh.
Ok, let's try again for a moment with the controller.
Moment of terror and system lit up. Disk (CF card really) found. Boot. Back in business it seems.
Round of tests - everything checks out.
Power down. Install a replacement for the damaged capacitor. Power-up. Silence. Hmm.
Remove the capacitor - everything works. Whatever, if that's how it wants to work - so be it.

Couldn't find applicable driver for the IDE interface. Online searches don't even mention VL-300. The closest i saw was another thread on vogons for what appears to be an early version caching controller named VL-200. Drivers are incompatible.
Located the SCSI driver right away.

Unfortunately performance is disappointing for both IDE and SCSI. Tested in the Asus VLI PC.
IDE hits 1854Kb/s in Coretest, ~1750Kb/s buffered read and linear read speed in SpeedSys.
SCSI climbs a bit higher - 2722Kb/s in Coretest, 2587Kb/s in buffered read speed and 2353 leaner read speed in SpeedSys. Without a driver SCSI performance drops to below 1Mb/s. So the driver does something, but nearly not enough.

There are plenty of jumpers on the controller, but couldn't find a manual online.
Spent good amount of time testing different combinations. Discovered most of the settings by trial and error. Nothing affects performance. Of course, there is a chance i missed some magical combination.

Added this guy to the charts in the VLB SCSI/EIDE controllers post.

Finally soldered up the variable resistor on my LSD board. Discovered that pushing the voltage up to 3.8volts allows me to complete Quake timedemos with air cooling at 50x4. I can actually run all the dosbench tests except Doom at this voltage with air cooling. Windows is a no go. Quake108 is a nogo. So a bit of an improvement but not quite there.

Before this I did try my peltier at ~3.5 volts but it still creates condensation in my environment.

Edit: Now I’ve seem to have lost adjustment on this resistor, is it possible to turn these things too far one way or the other? I seem to be stuck at 3.73 🤣.

Remember looking at 4x50 but didn't capture notes/metrics because it was slower than 3x66.
One of the 5x86 ADW CPUs here can do 3x60 on air cooling but is not 100% stable if pushed hard enough.
It needs 5V Peltier help (possibly lower) to get into 3x66, but again - not fully stable.
For fully stability have to crank-up the Peltier voltage to levels where water condensation occurs.

Didn't use trimmers in my retro activities so no idea if you damaged the one you got.
Sounds like mechanical failure.

pshipkov wrote on 2020-07-13, 08:31:

I am going to dump here info about few more motherboards and other stuff. […]
Show full quote

I am going to dump here info about few more motherboards and other stuff.

ASUS ISA-386U3Q

An old new stock. Squeaky clean, manual, wrapping, etc.

This seems to be a 1993 model. Visually the motherboard looks great - tight and well organized.
There are pretty much no jumpers on it. There is one for the FPU, 2 for the cache configuration and that's pretty much it.
The BIOS lacks any sophistication - there are 3 parameters related to performance that can be set to "fast" or "slow".

It is a bit picky about memory. Had to try few different sets to find the right ones for it.
However its biggest drawback is the inability to handle properly CF cards. Concerning.
As a workaround i strapped a SCSI adapter and all was fine from that point.
The SCSI operates at 6.7Mb/s, which is not exactly stunning for 50MHz FSB.

The board overclocks to 50MHz with FPU and things are stable for DOS gaming, but for 3D rendering and in Windows i had to step down to 45MHz for complete stability.

https://www.petershipkov.com/temp/retro_pc_im … _isa-386u3q.jpg

Didn't bother running LightWave3D rendering test. It takes about 3 hours to complete and won't reveal anything surprising.

Conclusion:
I had high hopes for this motherboard, but it didn't quite hit the mark.
Issues with RAM, issues with CF cards, performance is so-so.
Otherwise it is a real looker. Not sure if pictures give it a justice.

Is there any chance I can get you to send me a digital copy of this motherboard manual. Last year I came across this board and had to do some repairs, just getting ready to set it up and wouldn't mind giving the manual a once over.

Thank you very much,

pshipkov wrote on 2022-01-17, 21:41:

Remember looking at 4x50 but didn't capture notes/metrics because it was slower than 3x66.
One of the 5x86 ADW CPUs here can do 3x60 on air cooling but is not 100% stable if pushed hard enough.

Considering the benches from that Russian dude linked in the fastest 486 thread, and considering the extra trouble to wring 66Mhz out of a motherboard, when I've got a couple that will do 60, and the relatively small gain at 200, I think I'll just shoot for 3x60 with an AMD when I get round to it.

@novanick
That motherboard is not with me anymore, but asked buyer if he can snap photos of the manual.
Will let you know what he says.

@bitwrangler
Agreed. From a practical standpoint (what?!) 4x50 is the thing to do.
We kind of beat the 180/200mhz horse to death already anyway.

Practical? Has anyone gotten one of these chips 100% stable on air at 180 or 200?

Using a peltier on any voltage is not practical IMO

maxtherabbit wrote on 2022-01-22, 14:23:

Practical? Has anyone gotten one of these chips 100% stable on air at 180 or 200?

Using a peltier on any voltage is not practical IMO

180 yes, no peltier needed with one chip I have.