[raymo]

You are getting nonsense error readings on both axes, and since the R.A.
and Dec drives are separate systems, the likelihood of both developing faults simultaneously is vanishingly small. The only likely fault is a gear retaining screw coming loose allowing the gear to cause a lot of backlash, and that, of course, would only affect one axis. The only connection between the systems is electronic, so the fault must lie either in the MCB or the hand controller.[ or just possibly a cable or one of it's connections]. I just remembered that several years ago there was a spate of faulty hand controller to mount cables; mine was one.
If your only problem is error readings, then the problem almost certainly lies in the MCB, as the hand controller only relays the
readings from the MCB to your LCD screen; it takes no active part in producing those readings. It only sends instructions to the motors when
using the control buttons or using Go To. I gather you put a meter on the
capacitors; if so, were the readings significantly below the 470 stated on the components? As you are aware, that caused my problem, which was
seemingly identical to yours. Hopefully someone will get you over the line eventually.
cheers raymo
P.S. Unfortunately I'm not at home, so cannot run the test for you.