Tandberg 1500 series

[Michael Maurice]

I recently restored two of these tape recorders. Both came back because after some time, both were exhibiting a vibrating noise, like a bearing.

In fact it wasn't a bearing, the noise was coming from the drive belt which was wildly vibrating.

I've no idea what is causing it or why its only when the machines have been running for some time.

Taking a leaf out of Philips book, I noticed they have little brushes which the belts run through, I have devised a similar arrangement and if successful will post some pictures tomorrow.

In the meantime has anyone had this problem before? What causes it and is there any other cure?

[Michael Maurice]

I have fitted the end of an artist’s brush to the chassis to hopefully dampen the belts vibrations.

[hillmanie]

Is it possible to identify the source of the vibration? Is it likely to be in the belt itself? Perhaps replacing the belt with a shorter, tighter one might help?
TT

[Michael Maurice]

I dont think it's the belt itself as it has the correct crossection and the correct tension.

Fitting a shorter belt would but excessive stress on the table bearings.

[TIMTAPE]

Michael, in the photo is that the motor pulley to the right? It looks like the belt is running on a smaller diameter as if for 60 Hz or am I missing something?

If so maybe the slightly lower tension would have an effect.

[Michael Maurice]

Yes that is the motor pulley and yes there are two steps the belt crosses over to the left of this pulley and rides in the lower step in one direction, the upper step in the other.

Please see the picture below

[TIMTAPE]

Ah, got you, as per normal Tandberg setup.

[ricard]

I'm wondering if the plastic pulleys underneath the real holders could be slightly warped, causing the belt to shift up and down ever so slightly, the resonant effect of the tightened belt then amplifying whatever motion there is.

[saxmaniac]

Probably teaching my granny to suck eggs but are the fast wind clutch felts touching the reel tables due to mis adjustment of the operating levers. If there's not the 1mm gap as spec in the manual you can get slight dragging causing vibration

[Michael Maurice]

The machines both of them were back with their owner. It would be one hell of a coincidence if the same clutch pulleys on both machines were warped and or the decks were misaligned in the same way. Of course not impossible.

[saxmaniac]

Unless it's the curse of non original spare belts, mine chirps for 15 mins or so until it all warms up. Not loudly enough to be a problem but probably just some grotty old knicker elastic used in the belt manufacture!

[Michael Maurice]

That could well be the problem. I bought it from a German seller on EBay, next time
I’ll try Lasse.

[Paulus.d]

I know it sounds silly but \i think I've had this and all I did was reverse the crossover the of the belt ..... which one goes over the other .....
The vibration being the belt rubbing on itself
Paul

[Michael Maurice]

The machine is designed so that belts do not touch where they cross over. I have reversed the crossover but it made no difference.

[ricard]

Originally Posted by Michael Maurice

It would be one hell of a coincidence if the same clutch pulleys on both machines were warped and or the decks were misaligned in the same way. Of course not impossible.

I would rather say that after this time, it would be the rule rather than the exception that the plastic pulleys have warped in some way, even if it is seldom detrimental to the proper operation of the macihne. Whenever I've dismantled a clutch assembly, it has struck me that there are usually fine cracks near the hub of the pulley, and there is often some warping. I think the plastic used is not completely stable over time. I suppose the good thing is that the cracks tend to alleviate some of the stress built up in the plastic which will help avoid it breaking completely.

And then the second part of the puzzle would be that the movement induced by the warped pulleys injects energy into the belt, which is slightly stretched and hence has a natural resonant frequency, ergo, the belt will tend to vibrate at its resonant frequency no matter exactly what the excitation frequency might be.

Tandberg have a specified how the belts should cross over in the service manual, I've found that sometimes that makes a difference, but mostly not.

On some of the older machines at least, there's a little loop of piano wire I think bolted to the speed changing assembly, which goes either side of the belt, seemingly avoiding it coming off the motor pulley should it vibrate too much. So I'm wondering if this was a problem seen even in the factory.

[Ted Kendall]

In period, Hellyer noted that he sometimes had to change a Tandberg belt to alleviate a "singing" noise.