Panasonic K-drive erratic despite alignment, new pulley?
 

The decks works fine in a NV-HD100. When I install it in a NV-HS800, the drive shows erratic behaviour. It loads the tape, but after pressing eject it stops in down position. After Power off/on the Capstan rotates.

Motor pulley and Modeswitch are already new. The only difference between both tests is the used board under the drive. The NV-HS800 has a 14-pin-connector to the right side of the mainboard, while it is a 12-pin connector on NV-HD100. It has to do with S-VHS tape detection.

So my question is: How likely is it, that the cause of the problem is on this board (LEDs, Reels)? Or would you suspect a faulty motor driver IC? The deck had a rotten pinch roller assy when it arrived and was jammed.

Power supply seems o.k. - all capacitors have an ESR < 1 Ohm.

Have you cleaned the contacts of the mode switch connector on the board, they can be really dirty.
Also a good idea is to redo welds a bit everywhere , sensors and on the underside of the drum; some models have a board other not depends)
These k-mech panny's they're a mess to work on, i mean it. I fixed one, was working fine for some time now acting a fool again.

K mechanism is good and reliable with well known parts what should be serviced (pinch roller shaft cleaning and lubrication, guide rail cleaning and lubrication). If it works in one machine but does not in another it is probably electronic issue. PS should be recapped anyway, but it is not panacea. So find technician. However HS800 has no line TBC so does not worth to waste time with it.

The contacts are already cleaned and I resoldered everything on the drive PCB. Yes, seems to be an electronic issue - either on drive PCB (LED/Reels) or on main/servo PCB (Loading motor drive IC or even System Control IC). That would be the first time for me.

I usually replace all capacitors in PS, but in this case it seems not necessary. They look good and have reasonable ESR values.

These K drives can be tricky and the engineer who created the motor pulley should have been fired. But overall the K-drive is reliable and fixable.

What is wrong with motor pulley? Did it attack you? :)
Or you mean loading motor link gear? That one should be replaced with new nylon. Do not use 3d prints.

I mean VDP1434 - know that as "motor pulley"

It is "link gear". Yes, it should be replaced. I replace them with new even if they have no crack.

https://www.ebay.de/itm/336380481914

I replaced all opto electronic parts (Q1501, Q1502, D1501, IC1501 and IC1502) on the board under the drive (Mechanism Connection C.B.A) against parts from a similar board (but with different connector) and now the drive is working!