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First post, by Albercik

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Hello All!

Recently, I've built a PC running a Pentium 166MMX processor on a Powertech MB532 motherboard (AT format). The problem is that there is almost no information on the internet regarding this mobo and I have a serious problem: it seems that my COM ports are not working. The mobo has its own controller with 10-pin headers for COM1 & COM2. I've bought a RS232 ports with a 10-pin connectors (both are DB9) and connected it to mobo.

The problem is that I can't get my mouse to work. It's been tested on another computer and it's working fine, but it's not detectable on my new toy. I've doble-checked my bios settings (not much to set - I just can enable or disable onboard com ports), the drivers in Windows are installed without any any warnings etc. I have no idea if the settings in the device manager are correct, but I've left them default. I've even installed a MS Mouse driver, but its not detecting a mouse during boot (from autoexec.bat).

My PC is running a Windows 98 SE.

Do you know if there could be a different pinouts for COM port header on the motherboard between the manufacturers or is this a standard? Maybe I'm missing something different?

And please - do not advise my to buy a PS/2 mouse as my PC ain't got no PS/2 ports 😉

Thank you in advance,
Tom

Last edited by Albercik on 2021-02-02, 08:56. Edited 1 time in total.

P MMX 166MHz, 64 MB, S3 Trio64V2/DX, SB Vibra 16 ISA, 40GB HDD
P III 650MHz, 640 MB, nVidia Riva TNT2, SB 16 ISA, 120GB HDD
486 DX2 66MHz, 16 MB, Trident TVGA8900C, SB Vibra 16 ISA, 2GB CF

Reply 1 of 11, by Vynix

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I belive there are two types of COM port headers, there's a chance that your COM port brackets are wired for one type while your motherboard has the 2nd type.

Proud owner of a Shuttle HOT-555A 430VX motherboard and two wonderful retro laptops, namely a Compaq Armada 1700 [nonfunctional] and a HP Omnibook XE3-GC [fully working :p]

Reply 2 of 11, by Albercik

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Vynix wrote on 2021-02-01, 00:04:

I belive there are two types of COM port headers, there's a chance that your COM port brackets are wired for one type while your motherboard has the 2nd type.

Thatnk you, I didn't know that. I hope my mouse didn'got fried because of this...

Is there any way to re ognize which RS232 is which? It seems that I'll have to buy two new ports, but I have no idea how to check if they're going to be okay this time...

After a while of thinking - isn't the diffrence visible as a blind pin in the IDC connector? I've seen many COM now on google and the only major difference I've spotted was that IDC connector had either 10 pins or 9 pins (and 10th is blind).

P MMX 166MHz, 64 MB, S3 Trio64V2/DX, SB Vibra 16 ISA, 40GB HDD
P III 650MHz, 640 MB, nVidia Riva TNT2, SB 16 ISA, 120GB HDD
486 DX2 66MHz, 16 MB, Trident TVGA8900C, SB Vibra 16 ISA, 2GB CF

Reply 3 of 11, by majestyk

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There are indeed two types of connectors (both use 9 pins):
1. The more regular one
2. The one I call the "Supermicro" type, because Supermicro used it but others as well.

There´s no difference at the mainboard connector side, you only have to make sure Pin1 of the cable(red) sits at Pin 1 of the mainboard connector.

But when you remove the hood over the socket at the bracket (disassemble it) you can see the difference. The 9 wires are either connected row by row or "zig zag".
Just take a picture.
If you have the most basic soldering skills, you can resolder the connectors.
The problem when you buy these things is you don´t know what you´re gonna get in most cases. Using the wrong version usually doesn´t do any damage to the connected peripherals.

Here´s some additional info:
https://strugglers.net/~andy/blog/2015/06/19/ … serial-headers/

Reply 4 of 11, by evasive

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Header on the motherboard is numbered either

1 2 3 4 5
6 7 8 9

or

1 3 5 7 9
2 4 6 8

Usually you can see
1
2

or

1
5

in the side, that will tell you which variant you have

Reply 5 of 11, by Albercik

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Hi Guys!

As usual - your help is irreplacable 😀 My motherboard ain't got no pin numbers for COM port header. The only way I can tell where pin1 should go is because there's a rectangle surrounding the header and one of the "walls" is thicker than the other ones as can be seen on the below photo:
Powertech-MB532-Ver-10-Socket-7-Motherboard-Intel-_57.jpg

This is almost identical mobo to mine (it's Powertech MB532 as mine), but this one is equipped with PS/2 ports onboard and mine is not.

It's a shame that the Internet lacks of documentation for this motherboard, but I'll to figure this out by myself (with your help 😉 ).

BTW is there any way I can verify the pin layout using a multimeter (eg. by looking for 5V and GND or similar)?

P MMX 166MHz, 64 MB, S3 Trio64V2/DX, SB Vibra 16 ISA, 40GB HDD
P III 650MHz, 640 MB, nVidia Riva TNT2, SB 16 ISA, 120GB HDD
486 DX2 66MHz, 16 MB, Trident TVGA8900C, SB Vibra 16 ISA, 2GB CF

Reply 6 of 11, by Albercik

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evasive wrote on 2021-02-01, 08:37:
[…]
Show full quote
1 2 3 4 5
6 7 8 9

Ok, I've checked my serial port and it seems that this is the layout of mine COM port. Now, how can I tell if this is the correct pin layout for my mobo?

Tom

P MMX 166MHz, 64 MB, S3 Trio64V2/DX, SB Vibra 16 ISA, 40GB HDD
P III 650MHz, 640 MB, nVidia Riva TNT2, SB 16 ISA, 120GB HDD
486 DX2 66MHz, 16 MB, Trident TVGA8900C, SB Vibra 16 ISA, 2GB CF

Reply 7 of 11, by Ydee

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Seems like pin 1 for COM header is upper right - manual here:

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Reply 8 of 11, by PARKE

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Keep in mind that the pinouts of the motherboard sockets are mirror images of the 10-pin plugs on the adapter cables.
Finding the ground pin is the simplest way to determine which type of motherboard you have but I am not sure if you can do that with a multimeter.
Maybe this image helps:

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Reply 9 of 11, by majestyk

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Ydee wrote on 2021-02-01, 16:22:

Seems like pin 1 for COM header is upper right - manual here:

As I see it, pin 1 is on the upper LEFT - as usual.

Checking the position of the GND pin is a good idea.
But we still don´t know which version the current adaptor supports. There´s no way around opening the connector at the slot plate.

Reply 11 of 11, by Albercik

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Guys, you're genious!

I've took my COM port out of the case, and checked it (as I've wrote in previous post). It turned out, it has a "supermicro" pin layout (1 6 2 7 3 8 4 9 5).

Next, I've found some old COM port in my basement and checked it - pin layout is 1 2 3 4 5 6 7 8 9. Should work, but... it had 9-pin mobo connector (the 10th pin is blind).

So, I've disassembled both connectors and swapped them. Unfortunately - the supermicro com port has not soldered ribbon cable, so resoldering it was not an option. Thankfully - after swapping the connectors, my mouse started to work out of the box!

I wouldn't accomplish that mission without your help, so biiig thank you All!!

P MMX 166MHz, 64 MB, S3 Trio64V2/DX, SB Vibra 16 ISA, 40GB HDD
P III 650MHz, 640 MB, nVidia Riva TNT2, SB 16 ISA, 120GB HDD
486 DX2 66MHz, 16 MB, Trident TVGA8900C, SB Vibra 16 ISA, 2GB CF