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Need Help Identifying Cyrix MediaGX Motherboard and using ATX Power

gatewayrepairs1985

gatewayrepairs1985

Experienced Member
Joined
Dec 10, 2021
Messages
104
Location
South Of Boston, MA
Hi all,

I hope you had a wonderful holiday. Writing today as I have a motherboard (photo attached) with a Cyrix MediaGX processor. I have been able to find absolutely no information on the motherboard. It has no model markings anywhere on it. I have gotten it to POST with the traditional power connector (picture shown) but I want to put the motherboard in an ATX case. I have plugged in the ATX power connector, but then (as I show in the attached photos) I have no clue how to attach this connector from the power button on my case to the appropriate header on the motherboard. I’d like to find out more information about this board. And. how can I get this motherboard to boot with an ATX power supply? Thank you so much for any help you can provide! I appreciate it!
 

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twolazy said:
07/01/1998-GXm-Cx5520-2A433D09C-00 - Dataexpert MGX7520


DataExpert MGX7520 (SLIM)

DataExpert MGX7520 (SLIM) is a motherboard based on the Cyrix Cx5520 (GXi) chipset. Get specs, BIOS, documentation and more!
theretroweb.com theretroweb.com

Jumper settings
Click to expand...
@twolazy to the rescue! Thanks so much for the information! I don’t see any jumpers I would need to change, right? So I’m still confused as to how I can hook up this power button connector to the motherboard. Any advice would be greatly appreciated - and thank you for the information, I appreciate it!
 
bostonvintage1993 said:
@twolazy to the rescue! Thanks so much for the information! I don’t see any jumpers I would need to change, right? So I’m still confused as to how I can hook up this power button connector to the motherboard. Any advice would be greatly appreciated - and thank you for the information, I appreciate it!
Click to expand...

The pinout legend is silk screened on each side of the connector on the PCB.

In order to make the connector block you have work, you'll have to pull the pins out of the block and put them in the appropriate holes. This is not hard to do, you just need a sharp knife to lever the pin retainers up to let go of the pins. Just don't bend the pin retainers too much, or you'll break them. Generally all of the wires with the same color are negative, and the different colors are positive. The LEDs are polarity sensitive and won't work backwards. The power and reset buttons don't matter and will work either way.

Another option would be to buy 2 pin dupont headers, if you don't want to deal with the large block group of pins. You can just break out each LED/switch to its' own dupont connector.
www.ebay.com

620x Male Dupont Wire Header Connector Crimp Pin Housing Kit Female Jumper Pin | eBay

In addition to male and female crimp pins, the kit is also equipped with the most common DuPont pin housing. 200 Male crimp pin. 200 Female crimping pin. All in a high-quality housing. These are suitable for all typical and breadboard style pin connectors and sockets.
www.ebay.com
 
GiGaBiTe said:
The pinout legend is silk screened on each side of the connector on the PCB.

In order to make the connector block you have work, you'll have to pull the pins out of the block and put them in the appropriate holes. This is not hard to do, you just need a sharp knife to lever the pin retainers up to let go of the pins. Just don't bend the pin retainers too much, or you'll break them. Generally all of the wires with the same color are negative, and the different colors are positive. The LEDs are polarity sensitive and won't work backwards. The power and reset buttons don't matter and will work either way.

Another option would be to buy 2 pin dupont headers, if you don't want to deal with the large block group of pins. You can just break out each LED/switch to its' own dupont connector.
www.ebay.com

620x Male Dupont Wire Header Connector Crimp Pin Housing Kit Female Jumper Pin | eBay

In addition to male and female crimp pins, the kit is also equipped with the most common DuPont pin housing. 200 Male crimp pin. 200 Female crimping pin. All in a high-quality housing. These are suitable for all typical and breadboard style pin connectors and sockets.
www.ebay.com
Click to expand...
Hi,

This is awesome advice, thank you! I’ll let you know how it goes! I really appreciate it.
 
Hi everyone,

I still can’t seem to get this board to power on using ATX power. Under the traditional AT connector, everything powers on great - I get a power led, and the reset button works. However, when I try to use the soft power connector on the motherboard and my ATX power supply, nothing powers on. I am following this diagram here I found in the manual.

1676151885926.png

The ATX power supply is known to be good, and I only plug in the power button connectors when I’m trying to test. Does anyone have any idea what might be causing this? I could really use some help, thanks!
 
You should be able to short the green pair of pins and turn the board on.

If it doesn't turn on with an ATX power supply, does your ATX power supply have a -5v rail? This was removed from the ATX spec in 2003/2004, so if you have an ATX PSU newer than that, you're likely missing it. Many older AT and early ATX motherboards won't power on if the -5v rail is missing.
 
GiGaBiTe said:
You should be able to short the green pair of pins and turn the board on.

If it doesn't turn on with an ATX power supply, does your ATX power supply have a -5v rail? This was removed from the ATX spec in 2003/2004, so if you have an ATX PSU newer than that, you're likely missing it. Many older AT and early ATX motherboards won't power on if the -5v rail is missing.
Click to expand...
Hi,

Thanks for the help. Yes, my power supply is older and has the -5v rail. I was able to short those green pins once to get the board to power on about a month ago, but now I can’t replicate the results. When I short those two green pins, nothing happens anymore. Any idea what could be going wrong?

Again, thanks for the reply!
 
Just for reference, here is my current setup. When I press the power button, nothing happens. I do not understand why, as I believe this follows the diagram. Last time I tried booting this up with ATX it worked. Now I get nothing when I press the button.
 

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If it still works with an AT style PSU with the P8/P9 connectors, but not ATX, I'd suspect something being wrong with the ATX PSU.

Try a different power supply with a -5v rail if you haven't already.
 
GiGaBiTe said:
If it still works with an AT style PSU with the P8/P9 connectors, but not ATX, I'd suspect something being wrong with the ATX PSU.

Try a different power supply with a -5v rail if you haven't already.
Click to expand...
Thanks for the tip. I already tried another power supply and got the same results. I suspect the resistors near the connector may have blown. Do you know how I could check those/seek some replacements? Or is it not feasible to fix those?

Thank you for the advice!
 
What resistors? I don't see anything near the power connector but capacitors.

If some resistors have blown, there is something very wrong with the board that would require extensive surgery to repair. Resistors don't blow up for no reason.

If an AT power supply works, you need to do some continuity testing between the AT and ATX power connectors and figure out what's not connected on the ATX side. You also need to do a resistance check to ground on all of the power pins to make sure the board isn't shorted out. And ATX power supply won't turn on if it detects a short to prevent fire.

Also, is this junk on the board, or is the trace damaged?
CMPmDPJ.png


That's an important power trace, if it's damaged, the board isn't going to work.

There's also something going on with the regulator on the bottom right of the board. The transistor/mosfet next to the large diode looks burnt, and the solder looks equally cooked. If the board in that area being brown is an indication, that area has been getting smoking hot for a very long time.
 
GiGaBiTe said:
What resistors? I don't see anything near the power connector but capacitors.

If some resistors have blown, there is something very wrong with the board that would require extensive surgery to repair. Resistors don't blow up for no reason.

If an AT power supply works, you need to do some continuity testing between the AT and ATX power connectors and figure out what's not connected on the ATX side. You also need to do a resistance check to ground on all of the power pins to make sure the board isn't shorted out. And ATX power supply won't turn on if it detects a short to prevent fire.

Also, is this junk on the board, or is the trace damaged?
CMPmDPJ.png


That's an important power trace, if it's damaged, the board isn't going to work.

There's also something going on with the regulator on the bottom right of the board. The transistor/mosfet next to the large diode looks burnt, and the solder looks equally cooked. If the board in that area being brown is an indication, that area has been getting smoking hot for a very long time.
Click to expand...
Hi,

I was told there were resistors near the power connector but I don’t see any either. Was just seeing if maybe you saw something I was missing.

Good eye on that trace! However, I looked up another picture of this board and it has the same hole. It’s perfectly round - so I think it’s intentional.

What should I do about that issue on the bottom right of the motherboard? Could that be causing the ATX power to not work? I still find it quite odd the AT power works but the ATX doesn’t.

Thanks for all your help!
 
bostonvintage1993 said:
Good eye on that trace! However, I looked up another picture of this board and it has the same hole. It’s perfectly round - so I think it’s intentional.
Click to expand...

It's a VIA, and a really dumb place to put one because it removes something like 95% of the trace, significantly reducing its capacity to carry power.

bostonvintage1993 said:
What should I do about that issue on the bottom right of the motherboard? Could that be causing the ATX power to not work? I still find it quite odd the AT power works but the ATX doesn’t.
Click to expand...

The issue with the power regulation circuitry is different from the no-power from ATX issue. I would recommend resoldering the tab on the transistor/mosfet to get rid of the oxidized junk and put as big of a heatsink on it as possible, as well as a fan blowing on both it and the large diode next to it. Motherboards in the mid 90's had crap power regulation circuitry that often ran smoking hot, which would eventually burn out or damage the PCB. You can already see the PCB under those components turning brown from the heat, you need to do whatever possible to stop it from continuing on. Chiefly among them, active cooling. A small fan pointing at that area of the board with a heatsink on the mosfet would help quite a bit.

as for the no-power ATX issue, it could be a multitude of things. The ATX supply itself could be bad, if you haven't tried multiple units. There could be broken connections between the ATX and AT power connections, you could use a multimeter to verify those. The soft start circuitry could be bad, you'd have to reverse engineer that circuit and figure out what is wrong with it.

A bit risky, but you can try force starting the board with an ATX supply by backprobing the PWR_ON pin (green wire near the lock tab) to ground (any black wire) and see if the board boots. There is a risk of causing damage if there is a fault with that ATX power connector.

I would honestly just use an AT power supply, or an adapter and leave the ATX power connector well enough alone. If it works, just keep using it as is.
 
bostonvintage1993 said:
Just for reference, here is my current setup. When I press the power button, nothing happens. I do not understand why, as I believe this follows the diagram. Last time I tried booting this up with ATX it worked. Now I get nothing when I press the button.
Click to expand...
Have you tried jumping the PSW pins with a screwdriver? Your power button/wiring may be defective.
 
GiGaBiTe said:
It's a VIA, and a really dumb place to put one because it removes something like 95% of the trace, significantly reducing its capacity to carry power.



The issue with the power regulation circuitry is different from the no-power from ATX issue. I would recommend resoldering the tab on the transistor/mosfet to get rid of the oxidized junk and put as big of a heatsink on it as possible, as well as a fan blowing on both it and the large diode next to it. Motherboards in the mid 90's had crap power regulation circuitry that often ran smoking hot, which would eventually burn out or damage the PCB. You can already see the PCB under those components turning brown from the heat, you need to do whatever possible to stop it from continuing on. Chiefly among them, active cooling. A small fan pointing at that area of the board with a heatsink on the mosfet would help quite a bit.

as for the no-power ATX issue, it could be a multitude of things. The ATX supply itself could be bad, if you haven't tried multiple units. There could be broken connections between the ATX and AT power connections, you could use a multimeter to verify those. The soft start circuitry could be bad, you'd have to reverse engineer that circuit and figure out what is wrong with it.

A bit risky, but you can try force starting the board with an ATX supply by backprobing the PWR_ON pin (green wire near the lock tab) to ground (any black wire) and see if the board boots. There is a risk of causing damage if there is a fault with that ATX power connector.

I would honestly just use an AT power supply, or an adapter and leave the ATX power connector well enough alone. If it works, just keep using it as is.
Click to expand...
Hi @GiGaBiTe,

Thanks for the advice! I think I’m just going to use the board in a case with an AT power supply, I’ll find another board for this project. And I really appreciate the tips about cooling that part of the board. I’ll be sure to do that when I find another place for the board.

Thanks again for all the help, and I hope you are well!
 
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