Recently been working on this unit, I actually have 2, one in pretty good exterior shape and one for parts that's pretty ugly outside. Both units are exhibiting the same issue. In reverse playback and rewind, there is a very sharp POP in the right channel every so often. After a few times it genuinely hurts to hear it. It happens when the belt is on, but not when it's off, as well as whether a tape is in or not. The sound does not happen in forward playback, only the typical motor hum is present. Both units had pretty rattly motors, I tried adding a tiny bit of watch oil on the shaft but that made the noise significantly worse so I cleaned it out the best I can without disassembling the motor. I've also checked and the ground is making perfectly good contact. This one is pretty tricky to poke around on as you need to install the back to power the units off the batteries and I don't have a 6v wall wart laying around. Something's telling me the problem is with the motor, and I just happened to get 2 units with a bad motor but I have been wrong before so I would believe it if it were anything else. Any ideas? As I was writing this, the tick seems to have quieted down on one of the machines (unfortunately the ugly one) but it's still there. Inaudible when music is playing but if you put in a blank tape you can hear it under the hiss.
The other thing I forgot to mention is that the popping is dependent on volume. If the volume goes up so does the sound but when turned all the way down it disappears.
An update to this I discovered this evening. The tick is still present on forward, but significantly quieter. Almost inaudible in the motor hum. Also the tick disappears if the player is face down. There is some vertical play in the motor pulley but I assumed that was normal as I've seen it on plenty of other players. With the player face down the motor is resting at it's bottom position and with it face up maybe something inside the motor is moving and coming into contact. Would there be a way to remove that vertical play?
Ignore that part it was just an insane coincidence. Coming back and testing it again after the player sat for an hour the orientation does not seem to have an effect on the ticking.
After a bit more testing and thinking on it, I've come to the conclusion that the replacement belt I ordered from Turntableneedles is too tight. I dug through the trash and found the original belt and with that on the noise has disappeared completely. Luckily with these Sanyos the original belt is almost always in working order. Must be some different rubber they were using. I'm going to reach out to them and see if I can order a few that are slightly larger in size and try and get the best fit
The ticking is likely back EMF from the motor (from sparks at the commutator-brush contact). Fact a larger belt eliminates the problem means the tighter belt was adding too much load on the motor, increasing the current draw and sparks at the commutator. A belt that's too tight isn't desirable anyway, since it will wear the motor and capstan bearings due to increased load. As for the motor up/down play, that is normal, any motor has it. But the magnetic field should keep the rotor in a fixed position.
Thank you for the information! Are sparks at the commutator something that is always happening and the tighter belt was just producing more of it? The inside of motors are unfamiliar territory for me
Yes, sparks at the commutator are always produced because the windings of the rotor act as an inductor: it charges when powered, then stores energy as magnetic field. When inductor is disconnected (but has energy stored) from circuit (commutator moves to next winding), the voltage gets very high due to no load. This creates sparks, which become larger the higher the current through the windings is (the higher the current, more energy stored in the inductor). Inductors Explained - The basics how inductors work working principle
As a final update on this post, that was exactly the problem. On a Sanyo M-G55 the correct belt size is closer to 9.2 inches as opposed to the 8.6 inch belt they say fits it. Now I've got a quieter mechanism, smoother playback, and best of all absolutely zero popping!
