A couple other details:

1) Both with and without the breakout box connected, no IRQ is received.
2) The MIDI input accepts no data whatsoever, even in polling mode.
3) Both outputs work perfectly

Thanks for Great Hierophant for his input thus far.

Formulator wrote:

Please see the image. I opened the breakout box and saw this. Should this cable be connected?

That wire is the ground between the breakout box and interface card, and very-much should be connected. If you disconnect the entire connector, you should be able to get the pin back in beside the gray wire, where it belongs, without too much trouble.

OK, MIDI input is now receiving data! I wonder how that came undone. Those are hard to get out. SHOWIRQ still displays no MPU-401 received. Please confirm replacement of HD74LS05P on IC12. This sounds like the same issue GH was having last year.

For some reason, Cakewalk 4.0E DOS will not launch...just hangs at the title screen.

If your problem was the same as mine, I would suggest replacing IC12. I would also suggest that Cakewalk crashes because it detects an MPU-401 and checks for an IRQ that it will never received.

Before going through the trouble of replacing the hex inverter:

Does your system allow for adding wait states to the bus, and through that increase, is there any change in the MPU IRQ behavior?

Is there any change in behavior through use of a "stacks=0,0" entry in the CONFIG.SYS file? What about "stacks=9,256"?

Changing STACKS had no effect. As for the wait states, the BIOS (Award 3.03B1) has no option to adjust or jumpers on the motherboard. The only jumpers are for video, ports & EPROM type. I suppose it could be software driven but I do not have the original utilities disks for the system (Acer 915P). Since it is just a 286-10, would there even be an option to add wait states?

I have no experience with the Acer 915P, I'm afraid. Does it use IRQ 2/9 for the hard-drive, or some other system device? Can you try setting the MPU to a different IRQ than its 2/9 default, and then configure Cakewalk's MPU401 driver to use that IRQ instead ("cakepro -s").

Sorry for the tediousness; the likelihood that the 74LS04 is bad on yet another MPU card just isn't striking me as being very high. Do you have some other system in which the MPU-IPC-T can be tested, perchance?

I agree. Any solution that does not involve replacing IC's is preferred. I had also tried setting the MPU to IRQ7 and no difference with CW. The previous owner had the MPU set to IRQ7. I can possibly test on a different system Monday. I am also including a readout of IRQ activity on this system, for reference. I don't see any issues here:

OK, I have tested MPU card on 80586 system and it is receiving IRQ and is fully operational. This is good news, as I am pleased that I will need not embark on IC replacement. I must still figure out why my current system is not receiving IRQ.

Ah, the parrots have finally assisted. One of the them gripped the J3 jumper in from the 8800CS in their beak and all has been resolved. Regardless of the IRQ 09 assignment displayed here, Cakewalk must be set to IRQ 02 to successfully launch.