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Broken Supply and Take-Up Belts on the EIKI NT

The ailments with the EIKI NT did not end with the speaker repair.

While working on the projector, I discovered that the supply arm spool (the one at the front of the projector) was not taking up the film as it should when the projector is put into reverse.

Removing the cover from the supply arm revealed that the rubber belt which drives the supply spindle was broken in two places. It might have been that way for a while because I was not in the habit of using the projector in reverse or using it to rewind film. (See section below “The Mechanics of the EIKI NT Supply Arm”.)

photo of broken belt
The belt removed from the EIKI NT was broken in two places and had signs of fine cracks elsewhere also.

It must have been Belt-Breakage Month because shortly thereafter the take-up reel stopped taking up the film — the culprit turned out to be a broken belt in the take-up arm! Letting the film spill onto the floor is a definite no-no, so while the feed arm belt could be done without, the take-up arm belt was a necessity.

Thankfully Frank Arnstein from “Projector Heaven” was able to supply me with a replacement for each broken belt.

Genuine replacement parts for these decades-old machines are not easy to come by and these replacement belts didn’t match the originals exactly and were not a perfect fit — both belts were thicker than the originals and only just cleared the arm housings. But they did a good enough job and rendered the machine serviceable again.

photo of new thicker belt fitted into the supply arm
The new thicker belt fitted into the supply arm of the EIKI NT.

But one thing seems to lead to another and the next thing I noticed was that the automatic film loading guide was not retracting easily.

That’s the subject of the next post.

The Mechanics of the EIKI NT Supply Arm

Before leaving this topic, here are some more details about the working of the supply arm on the EIKI NT.

When projecting film forwards, the supply sprocket will draw film into the projector at its own rate. In this case the supply reel needs to be able to rotate freely. This is controlled by a one-way clutch, so it will turn easily in one direction to allow the film to come off the reel while locking in the other direction.

When you want to rewind the film or play in reverse, the roles of supply and take-up reels are reversed and the supply spindle needs to turn in the other direction to drive the reel.

Reverse drive of the supply reel can happen in two ways:

  1. Firstly for playing film in reverse the reel needs to be driven in reverse to take up the film, but with a clutch that will provide slippage so that the film is not pulled tightly and broken.

  2. Secondly for fast-rewind, there needs to be a much faster and firmer drive to the supply reel. This is achieved via direct gear drive to the supply arm. This direct gear drive is engaged when you flip down the plastic feed-in guide.

The following diagrams (copied from a scan of the the EIKI NT Service Manual, with some added colour) illustrate these mechanisms:

Illustration from the EIKI service manual showing operation of the rewind lever
Illustration from the EIKI service manual showing operation of the rewind lever which engages direct gear drive to the supply arm.
photo of internal speaker in rear cover
Illustration of the internal drive mechanisms for the supply reel. The series of three white gears on the left are engaged for fast rewind. For normal operation, the frontmost grey rubber belt drives the supply reel.