Hello and welcome,
so first you should put an image of the motherboard, then maybe also one of the CPU VRM area, the one with the mosfets (do they have cooling fins?), already from the images you can see if it supports dual-voltage CPUs, perhaps it could be a software problem, that is, if it doesn't recognize the K6s, it may be that they are not recognized by the BIOS, so perhaps the initial BIOS screen should also be photographed, just to understand what you have in that card.
Then of course there could be a HW problem, but first you need to be sure that everything is ok, so maybe even a photo of the jumpers, to select CPU and voltage.
Finally, the fastest dual voltage CPUs require switching regulators, I don't know if they are there in the MB one, I think you have linear regulators, in that case the more you go up in frequency, the more heat they develop, above 200 they start to be quite hot, but if you want to stay at 200 MHz, I recommend you add an additional fan.

Mobo manual;

https://www.zida-bios.com/download-datasheets … -with-id-6.html

Tried Pentium MMX. Manual settings of jumpers:
as in picture 6248

Voltage set to 2.8

V0 1-2
V1 1-2
V2 1-2
V3 2-3
V4 1-2

BF jumpers as in picture 6249

Ratio 3x

BF0 1-2
BF1 2-3
BF2 1-2

JP jumpers as in picture 6250

FSB set to 66Mhz
Jp4 1-3, 2-4
JP5 1-2

JP14
set 1-2 easy bios mode
set 2-3 manual

First set to manual. NO boot at all.

With easy jumper mode, JP14 set to 1-2

System at first boots, as Pentium-166MMX. Everything normal as it should be. Boots into dos, doscheck with sysinfo etc. No problem.

Second boot entered into bios, as seen in picture 6262, set to 3x, 200Mhz.

Boots to picture 6263, no keyboard response, frozen. No memory check etc. PCI analyzer gives two codes as

Continues....

Mobo VRM

PCI bios analyzer gives two codes one for award one for itself, I couldnt resolve correctly;

I think about possibilities;

1.Mobo ver 1.01 does not support over 166Mhz
2.Jumper settings are different for this version.
3.Jumpers are faulty does not connect.

Any ideas?

Jumper settings are probably incorrect.

https://theretroweb.com/motherboard/manual/35539.pdf

dominusprog wrote on 2024-01-10, 11:10:

Jumper settings are probably incorrect.

https://theretroweb.com/motherboard/manual/35539.pdf

Looked at this reference too. Jumpers are definitely in correct position.

Have you updated the BIOS?

fsinan wrote on 2024-01-10, 11:03:

Mobo VRM IMG_6251.jpg […]
Show full quote

Mobo VRM IMG_6251.jpg

PCI bios analyzer gives two codes one for award one for itself, I couldnt resolve correctly;

IMG_6269.jpg
IMG_6270.jpg

I think about possibilities;

1.Mobo ver 1.01 does not support over 166Mhz
2.Jumper settings are different for this version.
3.Jumpers are faulty does not connect.

Any ideas?

Ok looking at the jumper settings, everything seems fine to me.
Now we need to understand what blocks booting at 200 MHz, since it can be done from BIOS, I would try to select 180 MHz (60 FSB 3X), it seems strange but it is important if it starts, then we'll see if nothing changes.
A check that I would do, but you should do it, is a check of the voltage on the mosfets, you don't have to check all the pins, but only the upper part of the mosfet (opposite to the one with three pins), put the black tip of the tester in the molex dell ' power supply (black wire), and with the red lead test the VRM mosfets, obviously select VCC in the tester, I think up to 20V (depends on the tester).
One of the mosfets will certainly be 3.3V (or 3.5?), another should be 2.8V, if you don't find this value, that would probably be the problem.

dominusprog wrote on 2024-01-10, 16:26:

Have you updated the BIOS?

Good call! 😀

Hi fsinan,

An interesting and strange problem you have there!

To rule-out the BIOS as the cause, I have been looking into the VER2.6 (7/7/98) BIOS and found proper K6-2 support. However when testing this BIOS in a virtual i430TX machine in 86Box, I found that it would hang early during POST when using a CPU with MMX support.
So Pentium and WinChip C6 worked, but PentiumMMX and K6/K6-2 wouldn’t.
Very strange and I never saw this bug before on a socket 7 board.

Then I tested the VER2.3 (22/4/98) BIOS and that worked much better. All CPUs with MMX (except K6-2+/III+) worked fine now, including K6 and K6-2. Only with the K6-2 the BIOS indicated a K6(tm) 3D but this is just cosmetic.
Even the correct 2.20V Vcore was indicated in the BIOS, however the FSB/multiplier setting is limited to 66x4.5 (300MHz) in this BIOS version.

So my advise would be to try the VER2.3 BIOS and set Vcore/FSB/BF jumpers manually for your K6-2/366 AFR-66.

Regards, Jan

dominusprog wrote on 2024-01-10, 16:26:

Have you updated the BIOS?

It is latest 2.6 bios.

I don't know if this will help in your case as I own slightly older revision Zida Tomato 5STX 512KB (non-98) mobo and it refuses to boot at all if there's no healthy (2.8+ V) CMOS battery inserted. I own this board since 1998 and never had a single problem with it. Now it runs K6-2+ 500 (6 * 83 MHz) with modified BIOS.

Chkcpu wrote on 2024-01-10, 17:51:

Good call! :) […]
Show full quote

dominusprog wrote on 2024-01-10, 16:26:

Have you updated the BIOS?

Good call! 😀

Hi fsinan,

An interesting and strange problem you have there!

To rule-out the BIOS as the cause, I have been looking into the VER2.6 (7/7/98) BIOS and found proper K6-2 support. However when testing this BIOS in a virtual i430TX machine in 86Box, I found that it would hang early during POST when using a CPU with MMX support.
So Pentium and WinChip C6 worked, but PentiumMMX and K6/K6-2 wouldn’t.
Very strange and I never saw this bug before on a socket 7 board.

Then I tested the VER2.3 (22/4/98) BIOS and that worked much better. All CPUs with MMX (except K6-2+/III+) worked fine now, including K6 and K6-2. Only with the K6-2 the BIOS indicated a K6(tm) 3D but this is just cosmetic.
Even the correct 2.20V Vcore was indicated in the BIOS, however the FSB/multiplier setting is limited to 66x4.5 (300MHz) in this BIOS version.

So my advise would be to try the VER2.3 BIOS and set Vcore/FSB/BF jumpers manually for your K6-2/366 AFR-66.

Regards, Jan

Wow, thats' something. I'll try immediately.

fsinan wrote on 2024-01-10, 19:00:

Chkcpu wrote on 2024-01-10, 17:51:

Good call! :) […]
Show full quote

dominusprog wrote on 2024-01-10, 16:26:

Have you updated the BIOS?

Good call! 😀

Hi fsinan,

An interesting and strange problem you have there!

To rule-out the BIOS as the cause, I have been looking into the VER2.6 (7/7/98) BIOS and found proper K6-2 support. However when testing this BIOS in a virtual i430TX machine in 86Box, I found that it would hang early during POST when using a CPU with MMX support.
So Pentium and WinChip C6 worked, but PentiumMMX and K6/K6-2 wouldn’t.
Very strange and I never saw this bug before on a socket 7 board.

Then I tested the VER2.3 (22/4/98) BIOS and that worked much better. All CPUs with MMX (except K6-2+/III+) worked fine now, including K6 and K6-2. Only with the K6-2 the BIOS indicated a K6(tm) 3D but this is just cosmetic.
Even the correct 2.20V Vcore was indicated in the BIOS, however the FSB/multiplier setting is limited to 66x4.5 (300MHz) in this BIOS version.

So my advise would be to try the VER2.3 BIOS and set Vcore/FSB/BF jumpers manually for your K6-2/366 AFR-66.

Regards, Jan

Wow, thats' something. I'll try immediately.

Will check the CR2030 battery. Thanx!

fsinan wrote on 2024-01-10, 18:35:

dominusprog wrote on 2024-01-10, 16:26:

Have you updated the BIOS?

It is latest 2.6 bios.

According to what Jan writes, if you have BIOS 2.6, P.MMX and K6 will not work, so you should install version 2.3, which has verified and should solve the boot failure problem.
He also suggests using the K6-2 on manual settings, and if that works, I think you'll have it sorted.

PC@LIVE wrote on 2024-01-10, 16:59:

Ok looking at the jumper settings, everything seems fine to me. Now we need to understand what blocks booting at 200 MHz, since […]
Show full quote

fsinan wrote on 2024-01-10, 11:03:

Mobo VRM IMG_6251.jpg […]
Show full quote

Mobo VRM IMG_6251.jpg

PCI bios analyzer gives two codes one for award one for itself, I couldnt resolve correctly;

IMG_6269.jpg
IMG_6270.jpg

I think about possibilities;

1.Mobo ver 1.01 does not support over 166Mhz
2.Jumper settings are different for this version.
3.Jumpers are faulty does not connect.

Any ideas?

Ok looking at the jumper settings, everything seems fine to me.
Now we need to understand what blocks booting at 200 MHz, since it can be done from BIOS, I would try to select 180 MHz (60 FSB 3X), it seems strange but it is important if it starts, then we'll see if nothing changes.
A check that I would do, but you should do it, is a check of the voltage on the mosfets, you don't have to check all the pins, but only the upper part of the mosfet (opposite to the one with three pins), put the black tip of the tester in the molex dell ' power supply (black wire), and with the red lead test the VRM mosfets, obviously select VCC in the tester, I think up to 20V (depends on the tester).
One of the mosfets will certainly be 3.3V (or 3.5?), another should be 2.8V, if you don't find this value, that would probably be the problem.

Here comes the strangest thing.

I immediately tested with my thrusty 😀 Mastech..

Two boots performed. Detected as Pentium MMX 200. Bios easy jumper nor manual. Manual does not work at all as I've wrote. First boot resulted with memory testing and hanged.

Here are the readings in order from mosfets near to bios chip, 5.10V

the one near to board edge, 2.23V I dont know if it is relevant or not...

the one near to cpu. 2.68V, it is probably CPU feed

Lover than it should be as 2.8.

Second boot could not perform Memory test.
These are the results in same order;
again 5.12
this time 1.46
this time 2.23 Much lower than 2.8.

Voltage dropped as I understand at the output of the VRM at second boot and it couldn't perform even memory count.

So changing voltage results. Maybe a faulty mosfet here. Probably. Or struggling bios code.

PC@LIVE wrote on 2024-01-10, 19:13:

fsinan wrote on 2024-01-10, 18:35:

dominusprog wrote on 2024-01-10, 16:26:

Have you updated the BIOS?

It is latest 2.6 bios.

According to what Jan writes, if you have BIOS 2.6, P.MMX and K6 will not work, so you should install version 2.3, which has verified and should solve the boot failure problem.
He also suggests using the K6-2 on manual settings, and if that works, I think you'll have it sorted.

Will try it. With a "proper" Pentium 😀

I also have a Zida 5STX that came to me with a burned out mosfet. The manual specifically states that you have to change a jumper if you use a normal Pentium or a Pentium MMX and that if you don't change the motherboard it will burn out. I have never felt like trying to find what mosfets it uses since the one that is burned out cannot be read anything and I don't know which one it is.
So these motherboards may be a little special with the Pentium MMX.

fsinan wrote on 2024-01-10, 19:21:

Here comes the strangest thing. […]
Show full quote

PC@LIVE wrote on 2024-01-10, 16:59:

Ok looking at the jumper settings, everything seems fine to me. Now we need to understand what blocks booting at 200 MHz, since […]
Show full quote

fsinan wrote on 2024-01-10, 11:03:

Mobo VRM IMG_6251.jpg […]
Show full quote

Mobo VRM IMG_6251.jpg

PCI bios analyzer gives two codes one for award one for itself, I couldnt resolve correctly;

IMG_6269.jpg
IMG_6270.jpg

I think about possibilities;

1.Mobo ver 1.01 does not support over 166Mhz
2.Jumper settings are different for this version.
3.Jumpers are faulty does not connect.

Any ideas?

Ok looking at the jumper settings, everything seems fine to me.
Now we need to understand what blocks booting at 200 MHz, since it can be done from BIOS, I would try to select 180 MHz (60 FSB 3X), it seems strange but it is important if it starts, then we'll see if nothing changes.
A check that I would do, but you should do it, is a check of the voltage on the mosfets, you don't have to check all the pins, but only the upper part of the mosfet (opposite to the one with three pins), put the black tip of the tester in the molex dell ' power supply (black wire), and with the red lead test the VRM mosfets, obviously select VCC in the tester, I think up to 20V (depends on the tester).
One of the mosfets will certainly be 3.3V (or 3.5?), another should be 2.8V, if you don't find this value, that would probably be the problem.

Here comes the strangest thing.

I immediately tested with my thrusty 😀 Mastech..

Two boots performed. Detected as Pentium MMX 200. Bios easy jumper nor manual. Manual does not work at all as I've wrote. First boot resulted with memory testing and hanged.

Here are the readings in order from mosfets near to bios chip, 5.10V IMG_6276.jpg
the one near to board edge, 2.23V I dont know if it is relevant or not...IMG_6277.jpg
the one near to cpu. 2.68V, it is probably CPU feed IMG_6278.jpg
Lover than it should be as 2.8.

Second boot could not perform Memory test.
These are the results in same order;
again 5.12
this time 1.46
this time 2.23 Much lower than 2.8.

Voltage dropped as I understand at the output of the VRM at second boot and it couldn't perform even memory count.

So changing voltage results. Maybe a faulty mosfet here. Probably. Or struggling bios code.

In my opinion there could be a problem, that there are 5V is normal I think, they probably come directly from the power supply, one of the voltages should be 3.3V, which would be that of the I/O, at most it could be around 3.5V, but not 2.2V or 2.7V, the second measurement is even stranger, but I think it is due to an adjustment of the BIOS, that is, it initially starts with values ​​that are not dangerous for the life of the CPU, and then having selected the type of CPU and the speed, adjusts the values ​​using the correct ones, I imagine they are stored in the BIOS, for example a 366 K6-2, has two voltages, 3.3V I/O and 2.2V VCORE, so in the mosfets you should have those voltages (more or less 0.1V).
But since Jan verified problems with BIOS 2.6, I would try version 2.3 first, maybe there is an incorrect voltage in version 2.6, and this would explain why it doesn't work, but if you use manual settings, you could see the voltages on the mosfets , if they do not change, there could be a problem with one or more mosfets, if they go to normal values, the mosfets are fine.

PC@LIVE wrote on 2024-01-10, 19:13:

fsinan wrote on 2024-01-10, 18:35:

dominusprog wrote on 2024-01-10, 16:26:

Have you updated the BIOS?

It is latest 2.6 bios.

According to what Jan writes, if you have BIOS 2.6, P.MMX and K6 will not work, so you should install version 2.3, which has verified and should solve the boot failure problem.
He also suggests using the K6-2 on manual settings, and if that works, I think you'll have it sorted.

Tried bios 2.3.

First boot, detected as pentium 125MMX, bios message appeared to set new cpu settings. Entered, set to 200MMX. Rebooted, frozen after memory count.

Tried 166. No success. Wll try K6-2 with manual settings tomorrow.

Some news here.

I've looked at the output of VRM for every manual setting.

Board gives approximately 0.7 volf below the setted voltage so set to 3.2 for Pentium MMX and booted and worked flawlessly at 2.6V. Bios version is 2.3.

Set 2.9 for K6-2 as it should be 2.9 but output is 1.2V. It doesnt change with jumper settings. I dont know that bios effects the voltage in this case but will look for 2.6 bios now.