For the last two or three posts I have been talking about my adventures working on a TEAC A-4010S reel-to-reel tape machine. In the last post I illustrated the process for checking the tension on the tape because the machine was applying too much force to the tapes and snapping them.
Once the base-line tape tension has been established we compare the values to those published in the service manual. I discovered that for some reason those values were way too high and it was not a surprise that the tapes were breaking.
The next trick, then, is to adjust the tension on the tape. This is done by making changes to what the service manual calls a “variable resister”.
In fact, this variable resister is, according to definition, a potentiometer. It has three leads and is adjustable. Look it up if you don’t believe me. The photo above shows one of three potentiometers in the TEAC A-4010S. The adjustments are made by sliding one of the two band that are wrapped around the resister part of the assembly. Depending on which adjustment is being made, forward or backward, left or right reel, thin tape or thick, one or the other band will be slid left or right on the resister. You can see the coiled wire that the bands come in contact with.
After and adjustment is made to the appropriate band, the tension is measured again. If the tension is not withing specification another adjustment is made to the potentiometer. This back and forth testing-adjustment-testing process continues until all the results are within spec.
Tedious, don’t you think? Well, right you are, but it has to be done.
Unfortunately, we made a disturbing discover. The center potentiometer has a broken band. It necessary values cannot be set because the device can’t be adjusted.
That means I have to dig up a new part. Where can I find new part like this for a 50-year old tape machine?
Stay tuned.