[SiriusHardware]

I wasn't sure. The fact that it seems to be at steady logic 1 (+5V) means that UG5 is not being continually reset back to a count of zero which I thought it possibly might be.

The way that chip (UG5) is wired up it should be working as a simple 4-bit upcounter. The _INIT line input going to the LOAD pin (11) can zero the counter by going low (0v) momentarily but as that is not happening, you should have a continuous binary count on the four outputs QA(8Mhz), QB(4MHz), QC(2Mhz), and QD (1Mhz, pin 7).

As you don't have the 1Mhz on pin 7, suspicion now falls back onto UG5 itself, so my question for you now is how would you feel about trying to change that IC?

Here's what that would involve.

1) Finding and ordering a replacement 74191 IC, and a socket for it.

2) If you don't already have a pair, order the smallest, sharpest, most needlepointed pair of electrical sidecutters you can find. The tips of the jaws have to be narrow enough to fit into the gaps on either side of an IC pin.

The steps below are to be done ONLY when you have a replacement IC and socket already sitting in front of you.

3) Snip the legs of the original 74191 IC high up, right next to the body of the IC, (never low down, next to the PCB pads and tracks). Once you've snipped all the legs you can remove the IC body leaving just the 16 legs sticking up out of the PCB. Melt the solder on each leg in turn and as the solder melts, use a pair of tweezers to withdraw the leg from the PCB. When all of the legs have been individually removed in this way use your solder sucker to clear the holes.

4) Fit the IC socket ensuring that you put the 'notch' at the right end, solder it in and fit the new IC.

Sacrificing the IC (as above) is the best way to remove it without damaging the PCB. You can replace the IC but you can't easily replace or repair the PCB, so if you must damage something it's better for it to be the IC.

If you had a pump assisted 'proper' desoldering iron I would suggest trying to remove the IC in one piece but I don't think that is the best approach for you at the stage you are at, and with the tools you have.