Strange Printer Port Issue Hercules GB-112 in 5150

[Tincanalley]

Has anyone seen this before? I have a 5150 and was using the parallel port on the Hercules GB-112 card. It has been sitting for about 6 months and I finally go around to reinstalling the machine in its new location. Upon connecting the Epson LQ-850 to the port and powering the printer on, it wouldn't do the initialization as normal. I pulled the cable to try a different one, but once the cable was removed, the printer finished initialization. I took the new cable and it did the same thing. If I plug it in while the printer is on, it stops working and unplugging the cable while one restarts the printer. Now this entire time, the PC is off and I'm certain there is no power to the motherboard or video card.

I tried the printer and cables on a PS/2 50Z and it worked fine. So there must be an issue with the port on the video card. Could the controller chip have died and is shorting a pin or two and the printer see this?

I know there is a chip on the card, "LPT 112" and a resistor pack next to it. There are also 9 capacitors along the connection of the parallel port. I will have to remove the board to see if those resistors are connected to port pins and test them if so.

My next step is to try it with the PC running, but I'm a bit hesitant as I don't want to damage the printer.

 

[modem7]

There are also 9 capacitors along the connection of the parallel port

Those capacitors are pretty standard. They are there to provide some RF filtering on some/most lines in/out of the connector.

In fact, the IBM Printer adapter also uses nine (on the eight data lines and the strobe line), per the last page of the document at [here].

Could the controller chip have died and is shorting a pin or two and the printer see this?

Possible.

This could be a problem on one of the output (o/p) control lines that the printer looks at.

At [here] is PARTEST.EXE, a DOS based parallel port tester for IBM PC family parallel ports. Per the screen shots at [here], if you run the NO LOOPBACK test against the parallel port on the Hercules GB-112 card, do the four 'Toggle of O/P line xxxx' tests pass ?

 

[Tincanalley]

Those capacitors are pretty standard. They are there to provide some RF filtering on some/most lines in/out of the connector.

In fact, the IBM Printer adapter also uses nine (on the eight data lines and the strobe line), per the last page of the document at [here].


Possible.

This could be a problem on one of the output (o/p) control lines that the printer looks at.

At [here] is PARTEST.EXE, a DOS based parallel port tester for IBM PC family parallel ports. Per the screen shots at [here], if you run the NO LOOPBACK test against the parallel port on the Hercules GB-112 card, do the four 'Toggle of O/P line xxxx' tests pass ?

I located my loopback adapter, so I'll be doing some diagnostics with and without it. So glad I saved all the test plugs I gathered over the years.

Here's what I discovered so far. If I plug the printer into the port, the printer will not finish initializing. If I turn on the PC, it finishes and seems to work in testing. However, rebooting the PC will make the printer restart. I wondering if there is something about the port that isn't working as the printer expects until the PC is turned on and the port initialized. Rebooting must disturb it again until the port reinitializes. None of the other machines I connect the printer to exhibit the behavior so there is either something non-standard about the port on the Hercules or there is a problem that goes away with power applied.