In my expirience the UIT for the door operator is interchangeable but the controller UIT is job specific. Possibly mechanical slippage causing the encoder count to go off? There are also hex head bolts that I have noticed have a tendency to loosen up over time.

You know, I haven’t watched it for Belt slipping. That’s a good idea to check. I appreciate the tip.

Also if this model has brushes in the door motor...I have seen some at half wear give problems

to put a UIT on the controller you will have to to the factory and get new software. You can put a UIT on the door operator if it is one of the newer PA boards (6300HL1 is the UIT part number). But an HD98 should be the older PY or even older FX boards. These older boards will act like this when they get old where you can’t get it to slowdown. I’m not really sure where you can go from here without IMS though, can’t do a scan or make adjustments. Do make sure it has the correct encoder though and use a meter to verify it works. The older boards get the big black optical encoder, the newer PA boards get the small digital encoder.

Also check the door operator linkage at the drive arm(s) at the operator and where the small arm attaches to the door. That stupid allen head machine bolt has a way of backing itself out to cause what you’re describing. Same with the set screw on the motor shaft, but you’d get encoder faults most likely.

I see UpandDown hit these issues...oops.

I have found that linkage bolt loose on other jobs, will definitely check that!

Tac 20 should have a py3 board with the large black encoder. Board is probably shot. Good luck

Went back yesterday and it only did it a couple times in the open direction in 30 minutes of running it. Yesterday was a cold day here, and cool in the hoistway.

The previous visit it exhibited the problem at both floors, open and close, and about 97% of the time - and it was a hot day and hot in the hoistway. Seems like there may be a temperature sensitivity, there..

Belts weren’t slipping, linkage right, brushes show hardly any wear. I’ll keep an eye on it.

.......common problem is the bearing on the sheave drive arm plate either goes bad or the bolt that attaches the arm looses up or is broken.excessive play will be seen on opening/closing cycles..slamming.....

Without ims your screwed

In my opinion it is very likely that door stroke is not set properly. I see this all the time, stroke not set right, guys try to use electronic adjustments to compensate. It may work okay for a while, then a few years down the road it’s necessary to tweak parameters. If door stroke is mechanically set right you can damn near use default parameters. Hard to explain step by step to get it perfect, but TKE or Dover manual for any vintage HD operator will explain stroke adjustment.

The other possibility is that belts were never loosened when operator was new. What I mean is the factory sent out all HD operators, the belts are always WAY to tight. They need to be as loose as possible to barely keep traction on reversal. Knowing this sometimes people incorrectly increase torque settings to compensate for tight belts. Then belts loosen/stretch, or idler arm bearings starts to go out also loosening belts and now you got slamming doors.

As far as pick up rollers slipping out of clutch, score a cross hatch pattern/ or vertical lines in the face of the clutch closing vane with pocket knife . This is maintenance thing I do. Hold closing hall door being careful not to break the beam, if hall door slips out of clutch, start gouging the face of the closing vane.

For the doors coming uncoupled, I’ve had really good luck replacing or even doubling up the spring steel plates in those old clutches.