Attempted repair of fwd/rwd clutch assembly for 3-5286A aka Realistic SCR-6

[stragulus]

The mechanism for the deck in this boombox has a clutch assembly in the fwd/rwd drive. This assembly provides slippage when the tape is at the start or end so that the box will not break your tape.

Now while this deck's mechanism is pretty beefy for a boombox with lots of heavy steel parts and linkages, the clutch assembly sadly relies on plastic parts to stay together. Plastic parts that, as they age, shrink. Inevitably, due to the design, this will break the assembly. I Doubt there's a boombox of this type around today that still has this functioning well, but who knows they may have used different materials for different revisions.

Anyway, an illustration of how this assembly works will help explain the attempted repair. The different parts are:

• A bottom gear. This directly drives one of the 2 reels to rwd/fwd.
• A top gear. This one is driven by a gear on the main flywheel, which in turn is driven by the motor through the main drive belt
• A pin (axis?) running through both gears with a plastic cap on top to keep it in place
• A spring that pushes the top gear onto the bottom gear - this provides enough tension to make the bottom gear rotate when the top gear is driven, but when the bottom gear stops because the tape is at the end, the top gear will slip (there is felt in between the gears) to prevent all the driving force from putting too much tension on the bottom gear.

Now the reason this assembly breaks over time is that the whole thing sticks together just like lego bricks do by having 1 plastic part snugly snap onto another plastic part. The plastic shrinks with age, tension gets too high, and at some point the plastic will tear. The force of the spring controlling clutch tension will now break up the lego-like marrying of the plastic parts.

My attempt to fix this, is to replace the lego-like joint (there has to be a better term for this?) with epoxy glue. The parts that are joined together do not rotate relatively to each other, so this does not impact the function of the clutch assembly. To get the glue to set, things need to be clamped together, which needs some custom made jigs to keep everything in place the right way.

The pictures of all the various parts and jigs with some inline explanations:

All of the clutch assembly parts in the right order. The red plastic cap at the right is part of tthe jig. Notice how it has a little dimple in the middle? That is there to keep the jig in place as we clamp it. It cannot be a full hole as then the pin will not be restrained in place, which is very important. It must completely stick out the bottom end!



All the clutch parts assembled before the clamping. Notice the hole in the piece of wood (the other part of the jig). This is necessary as, when everything is clamped together, the pin will protrude from the bottom. Yet we still want to clamp it in place easily so now it can sit in this little hole.



This is how everything will be clamped together once the glue is applied. The spring sits inside now:


The bottom gear. The outside of the shaft is what needs to be glued. Notice in one of the pictures above that there's a plastic white cap on the pin. That cap slides onto this shaft here. When this was new, apparently this was a snug enough fit to not need glue to stick together. Now, not so much anymore!

I have made some grooves into the shaft's outside with a sharp blade, to hopefully better adhere to the glue. Care must be taken to not get glue on the horizontal plane of the gear as that is where the felt of the top gear sits on, and that should actually be able to rotate.


The plastic cap where the top part of the pin slides through. You can barely make it out but it is partly torn, causing the malfunction.


And here it is, all clamped together after applying the glue (I used JB Plastic weld, a 2 component epoxy). Let's just keep that in place for a day.



What do you think... will it work? I give it a 4 out of 10 chance.

 

[stragulus]

It holds, but the assembly is (still) driven out of its socket when engaged in fwd/rwd mode as shown in this video. It's so weird. There's nothing holding this thing in place other than the socket it sits and rotates in. You'd think it would be kept in place with a bracket just like the flywheel but nope, nothing.

EDIT: Ah, the socket it sits in is also cracked. Picture of its underside:


Lots of effort for this deck, I think it ends here. But, if you ever run into this, you now know where to look.

 

[stragulus]

Fine, for science, I will attempt a last ditch effort to fix this. I give this a 1 out of 10 chance of success, at this point I'm mostly curious whether it will do the trick. I put a piece of painter's tape under the plastic socket and slathered epoxy in an area where the plastic piece does not get in the way of anything else. I also dribbled some in the actual socket, with the idea of drilling a small new hole with my dremel once it has completely hardened.

 

[Fatdog]

What type of epoxy did you use? The default around here seems to be JB Weld. Did you scuff up the plastic a little bit beforehand?

 

[stragulus]

I used JB Plastic Weld. I wonder if regular JB weld (the gray stuff) would be better. It needs more time to harden but since this is all stuff that can be clamped in place that would have been fine. The regular JB weld has a higher tensile strength but the plastic weld is not far off.

I I made scratches in the plastic for the clutch assembly (tiny and hard to reach) to create more surface area for the epoxy.

 

[MesaAZGuy]

Thanks for posting. I am curious too if this will work out. I know these can get frustrating. I have a couple of radios with deck issues I haven't gone into yet.

 

[stragulus]

Fine, for science, I will attempt a last ditch effort to fix this. I give this a 1 out of 10 chance of success, at this point I'm mostly curious whether it will do the trick. I put a piece of painter's tape under the plastic socket and slathered epoxy in an area where the plastic piece does not get in the way of anything else. I also dribbled some in the actual socket, with the idea of drilling a small new hole with my dremel once it has completely hardened.

Sadly, that didn't change a single thing. It all fits together great but turning the flywheel with fwd/rwd engaged will still drive the clutch assembly out of its socket. It is a complete mystery to me how this was ever supposed to work mechanically. There's literally nothing that holds that thing in place. No groove in the axle underneath where a c-clip could have been. Nothing on top of it as that is where the flywheel rotates overhead. Very, very strange.

Anyway, good news is, you can just leave the clutch assembly out and it will only lose fwd/rwd but it does not impact playback in any way. So that's what I did and now it's all together playing again and pretty strongly at that!

 

[docs]

Did you check if there is a fiche of the deck just to be certain something is not missing?
Looks like an aka of a Ferguson-3T18. Perhaps the decks are identical.

 

[stragulus]

I found a service manual with a breakdown of the deck's mechanics. That seems to match with my understanding and observation. The relevant part (arrow points to the clutch, which is part of the rwd/fwd assembly called BO-49):



Not sure what a fiche is, the same thing but more detailed?

Maybe the clutch gets driven out of its socket because it doesn't mesh with the gear on the flywheel assembly at a straight angle. If you look at the video I posted a few posts above you can see that the clutch is slanted a little. This is true even after all the attempts to make it fit better. Hard to say why, but I suspect aged plastic parts. Given the nature of this mechanism I wonder who still has this functionality working well after all these years in this or the AKA's (that Ferguson, but also the Realistic SCR-6)