modem responds to 'AT' OK but 'ERROR' to all others

[leehinkleman]

A 56K Ellcon modem was working OK on Com2 until a HDD partition table error forced a format of Windows 95, which now finds 'a new port or modem adaptor attached...' but can't query the modem.
Hyperterminal receives 'OK' with an 'AT' command, but receives error with AT&F, AT&F1, AT&F2, ATZ, ATH, ATI0, ATI1, ATI2, and ATI3.
I tried sequences of '+++' and longer strings of plus symbols.
Two days ago, the modem did respond OK, but I had to remove it to try to modify the back rail, which couldn't be screwed to the tower.
Since then, it's been only partially responsive, as described above.
Could the problem be a bad connection in the ISA slot? The card feels physically quite loose in the slot.
Thanks for your help.

 

[leehinkleman]

The Ellcon modem is working now, after I sharpened the ISA slot terminal edgesof the card with a table belt sander, using an 80 grit belt. I made a practice run first with a dead 28k PCTel modem card, and then ground the Ellcon's edge on both sides to about a 30 degree angle, and then refined the edge with finer sandpaper on a wooden block.
The edge of the card must have been too blunt, and was forcing the ISA slot's contacts away from the modem's gold contacts, some of which were also ground down slightly.