Akai GX-77 reel to reel tape recorder.
A client asked me to have a look at their GX-77 that had been stored for many years. These were made in the early 1980s.
As soon as I got inside I could see that the belts needed replacing and that the mechanism was seized and the grease was dry and very sticky. Luckily they hadn't tried the machine as this can result in the loading cam gear breaking as it tries to fight against the dry grease and seized mechanism.
The mechanism needed to be stripped, cleaned of the old dry grease and fresh grease and lubrication applied. Complete removal of the mechanism is the best way. But as I looked closer, I could see that was not an option as quite a few connections are hard wired.
With the mechanism 'manoeuvred' into a position so I could work on it, The stripping and cleaning process begins. This is very time consuming.
After many hours, the mechanism is now running nice and free. Time to connect it back up and test the mechanical operation and, if all's well, the electronics can now be tested.
All the switches and controls required cleaning, but the rest of the electronics is working fine, as it usually is!
The full tape path is cleaned and degaussed. The machine is now back to a working condition.
However, on test I noticed that the fast winding was very slow near the end of the tape. So I started to make some tests to try and find out why.
After some investigation work, I concluded that there are several factors that cause the poor fast winding, 1) there is friction as the tape goes over the guides and heads 2) there is some resistance from the free running spool motor 3) old tapes can be a bit sticky, which doesn't help.
To confirm the friction through the tape path as a problem, I threaded the tape so it didn't go over the heads. The result was greatly improved fast winding. So I decided that if the free running motor had a small voltage applied to make it run in the correct direction, this would overcome the motor resistance and relieve the friction over the heads. So I designed a circuit with a couple of relays to switch some voltages to the two reel motors. I then had a look on the internet and found other engineers had come to a similar conclusion! Maybe I should have done that first!!!
After building my mod circuit and fitting it to the GX-77, we had perfect fast winding.