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I've just installed two identical fax modems into a Windows Server 2003 Standard server and for whatever reason, the first one works fine and the other doesn't. They both create virtual COM ports and using SysInternals PortMon, I can see that commands are being sent to the first modem okay, but nothing is sent to the second modem (even though the application attempts to communicate with it -- and fails opening the COM port).

I've seen lots of posts about this type of issue online, but I can't find an explanation for why I can't have two identical modems working side-by-side, or whether it is, or is not possible.

The second modem's going back if I can't get it working.

Matty Brown
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    Does the second modem work by itself in the server? – MDMarra Jun 05 '13 at 19:32
  • Yes, both cards are functional, as long as they're not installed in the server at the same time. Oddly, when both cards are present, Windows DUN (Dial Up Networking) can dial out using either card - it's only when software attempts to connect to the modems using their COM ports that one of them works and the other doesn't. – Matty Brown Jun 05 '13 at 20:32
  • You're still using a fax machine? – hookenz Jun 05 '13 at 21:04
  • Yes, unfortunately businesses do still use fax. Some customers are stuck in the dark ages and if we want their business, we have to accommodate them. I guess I can see why fax can be more convenient when you have to print, sign and return something... but personally if I can email something I'd rather do that than fax it. – Matty Brown Jun 06 '13 at 08:16

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sounds like a problem with the software not windows. can you send commands to both com ports and do they both respond independently? You should also ensure that the com ports are the ones on different IRQs (in the old days modems were set on irq 5 and 10 - for "performance")

Jim B
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  • Both modems are on different IRQ's. The first modem responds on its COM port - the second does not. I've seen comments on various websites that say identical modems will not work in Windows, but nothing substanciated. – Matty Brown Jun 06 '13 at 08:14
  • Make sure the com ports are enabled in the bios. Back in the day I've used multiple identical faxmodems, but its been a long time. If the comport is enabled but still doesn't respond, try changing the IRQ on the card. In a modern app the irq really shouldn't matter but if the old.school com2: isn't responding the reason is likely that something else is using that IRQ. While you're in the bios, disable every device you do not need (lpt ports etc) – Jim B Jun 06 '13 at 11:48
  • Hi Jim. The modems are PCI cards, so the COM ports aren't physical and aren't listed in BIOS. – Matty Brown Jun 06 '13 at 20:05
  • have you tried switching slots? It seems to me that somehow they are both hitting Com1 at the legacy level and unless they have some configuration, are conflicting. – Jim B Jun 10 '13 at 20:16