Another problem in the well known classical deck 480

As shown in the common repair on the 482, the sticking carriers for the pressure rollers are a common problem in the 480 series. As a matter of fact this problem sometimes occurs also in the other lines using the diffused resonance double capstan transport. In this classic Nakamichi transport the grease on the pivots on which the pressure roller carriers rotate transforms into gum with age. This thickened grease will finally glue the lot in stead of lubricate. The sticking carriers can block the functioning of the head base and cause other problems. The next photo (and link) shows the pivots without the accompanying carriers and pinch rollers.

A lesser known problem

Recently I came across a new problem in a sample of the Nakamichi 480. The take up reel hub was not effective in taking up tape. The torque was high and therefore the most common cause for take up problems did not apply here; slipping idler tire. In stead the take up was turning but not taking up the reel from the cassette tape. The tape deck was not shut off because the hub turned freely so after several seconds the tape piled up around the right capstan. With fast forward nothing happened but the hub was clicking away against the tape reel.

The cause proved to be a sticking outer hub which once pushed inside, did not return outwards and therefore did not engage in the tape reel. Not such a big deal, but I did not find a problem like this before.

How things are supposed to work

The hub in the cassette deck has three small ribs (fins) which will take up the ‘teeth’ inside the reels of the cassette tape. These ribs and teeth will align when the tape is inserted into deck, at the time the door is closed. The position of the ribs and teeth is undefined at the time the door is closed. It is possible, but unlikely, the ribs and teeth will exactly align when the door is pushed. This will block the reel to fit onto the hub. To avoid damage that might occur when the door is closed with force, the hubs in the Nakamichi transport can slide inwards. When the hubs slide into position behind the tape reel a spring is loaded, pushing the hub gently inwards. When the hubs start to rotate this instable balance of teeth and ribs gets disrupted and the hub will freely slide outwards aligning correctly against the reel teeth. Proper take up of the tape can now be accomplished.

(I hope this makes sense, try and take a good look at the reels and hubs while slowly loading a cassette in the compartment.)

What did not work properly in this case.

The spring would not return the hub into its outer position. Helping the spring would move the hub into the desired position and the deck would function normally. Manually pushing and pulling the hub to the outer most positions revealed too much friction and the spring was not able to overcome this amount of friction. This time the elevated level of friction could not be contributed to the old age of grease, for these parts are not greased at all! Lubricating did not work and to find the origin of the problem the hub needed to be taken out of the deck. The service manual is not very clear on disassembling the hubs. I gambled the parts are click fitted into place.

The parts under investigation are shown in fig 9.10, numbered 01 en 02. The cap number one 01 required attention first. This pyramid shaped component has the size of a match head and could not be pulled out using fingers only. Using pliers seemed unwise since no spare parts were in my possession. Using some toothpicks from a dentist (very handy tools!) the cap came loose and flipped out onto the floor. The rest was easy and parts 01 and 02 proved to be a set of five separate parts which can be slipped away from the thin spindle. But as a matter of fact, first the belt to the auto shut off mechanism had to be removed as well (…. and so the back of the cassette compartment, and the meter casing, and the front of the machine, and the top housing …) If the left hub had been the culprit these components could all be left alone. But faith had it this time the take up hub was the problem. So everything mentioned had to be disassembled thanks to the belt, in fact this is simple enough.

The hub is composed of an inner hub, a spring, outer hub which is loaded by the spring and an outer ring pushed into the end. Together with the already mentioned pyramid shaped the set looks like this:

The root of the problem

The top of the inner hub was a bit too thick so the outer hub was not moving freely up and down. Closely looking revealed a small crack in the plastic top of the inner hub. When the outer ring gets pushed into the outer end of the inner hub this ring will extend the inner hub a little, allowed by the crack. Trimming the inner hub with a small file proved helpful and solved the problem. Rebuilding the hub was next.

Rebuild:

The fault was removed and the deck was easily rebuilt. This sample of 480 worked fine but needed a full adjustment as the record/play head was completely out of alignment, remarkably so. When mechanically realigned the electrical alignment proved to be spot on. Listening to it is all that remains….