BSR turntable autochanger not working on 33rpm

[jackcoom53]

Hello everyone, I have recently just purchased an 1974 Fidelity stereo system. The seller did say that he has serviced it and that it was free running.

Well when I received it, it wasn't! So I stripped it down and cleaned and greased all the under the platter with silicone grease, tested it and it all worked fine for a few days, until a couple of days ago when the autochanger stopped working on the 45 and 33 rpm speeds!

So I have stripped it all down, cleaned all the grease off and used a light oil (3 in one) instead of the grease and the autochanger now works on the 45 and 78 rpm without any problems but it still won't work when the 33 rpm is selected. What happens is this, the arm will lift as the turntable rotates but then the turntable will start to slow down and stop, if you turn it by hand at this point it will pick up it's speed and then play the record as normal, it's like as if there isn't enough torque or force or whatever you want to call it on the speed to keep the turntable rotating for it to complete the cycle.

As I haven't done anything like this before with these I am hoping that someone of you tech guys and gals can tell em where I have went wrong and point me in the right direction.

Kind regards,

Jacky

[julie_m]

Something is still binding somewhere .....

Try this test: If you spin the stepped motor spindle between your fingers (with the idler disengaged), how long does it take to come to a stop? Give it a few tries if you have to, and post your results here.

This will give us an idea whether the problem lies in the motor bearings or the changer mechanism.

[john.north]

The idler tyre will need checking. If it is still soft it will need cleaning on the outer edge with isopropyl. Also the inside edge of the turntable. Oil the idler centre where it sits on its mount. Clean the motor pulley drives. Spin the motor by hand. If it doesn’t spin freely this will drop the torque considerably. The bearings will then need cleaning and oiling.
John.

[jackcoom53]

Hello everyone thank you for your quick replies. John I have already done what you suggested, the motor does spin freely. Julie I have also tried your suggestion and it does spin for maybe about 10-12 seconds before it finally stops.

What I find very strange is that it works totally fine on all other speeds but not 33rpm.

I have a video of it but being new on this forum I don't know if you can post videos on here so I will post it on my YouTube channel as soon as I get a chance,but please don't laugh at my bus videos!

Kind regards
Jacky

[ms660]

Make sure that the rubber idler wheel is only in contact with the 33rpm section of the motors stepped pulley when 33rpm speed is selected, you can check that with the platter removed.

Lawrence.

[john.north]

As Lawrence says make sure the idler tyre is only making contact with the 33 motor drive. Failing that I would re clean the idler tyre and the platter, oil the idler mount. Did you remove the cam and remove all the old grease before re-grease? It sounds like a low torque problem and will show up on a slower speed setting, and a sticky cam won’t help.
John.

[jackcoom53]

Hello lawrence and John, Lawrence I have tested that with the platter off and the idler wheel is in contact with the correct part of the motor spindle, I must admit I was hoping that it would be the problem but sorry to say that's it not. John your suggest sounds something along the same lines as me but that is where I am at a loss! What and where are the cams you have mentioned. Do they control the movement of the tone arm. The reason why I am asking is that the top "cam" (that is we are both talking about the same thing that is) appears to be seized unlike the on line videos that I have seen, but I may be totally wrong about the "cams".

[boxdoctor]

I would think that all the above cleaning and lubrication having been done, the most likely suspect is the one John (above) has mentioned, and that is the inside rim of the turntable. With everything in good fettle, the friction between this and the idler tyre normally is only just enough to power most changer mechanisms on 33R.P.M.
On the higher speeds the turntable has enough inertia to power it over the "tight" parts of the changer cycle. There can easily be a deficit on 33 R.P.M., as there is less inertial power stored in the turntable.
I would suggest that you most thoroughly clean the inside rim with Propanol, or methylated spirits, and remove any shine with a suitable fine abrasive.
Also carefully check for glaze on the edge of the idler pulley - the rubber may have gone hard i.e. perished.
Tony.

[julie_m]

This is true; kinetic energy = 0.5 * m * v**2. So when you increase the speed from 33 to 45, i.e. by a factor of 15/11, then you will increase the KE by a factor of 225/121, which is almost double. So it will have more stored energy to keep moving the rest of the changer mechanism without coming to a complete stop.

The idler drive relies on friction, and thus can only ever transmit a limited amount of torque. If the force required to move the turntable and whatever bits of the mechanism are connected to it at the time is greater than the force required to overcome the friction between the idler and the turntable rim, or that between the motor spindle and idler, then the idler will just slip (or if the motor cannot supply enough force it will stall, and could overheat if left too long in this state).

Don't use any solvent stronger than alcohol (meths or isopropanol) on the plastic turntable or the rubber idler wheel. Place a tiny drop of oil on the spindle on which the idler sits, after cleaning it and the hole in the idler wheel thoroughly.

If you get only a partial improvement after tending to the idler drive, that just means something downstream must still be binding. So unplug the record player from the mains and load a 17cm. record on the spindle. You should then be able to move the switch to AUTO, turn the turntable clockwise by hand and the changer will go through the usual drop and play cycle. This will let you feel for yourself exactly where each of the various actions occur, and which ones offer the most resistance; which in turn might give you some pointers where to look next.

[john.north]

If you are sure that the idler rubber is good and all surfaces are clean there should be plenty of gription (made up word) between motor and platter. You could put it in play mode without a record and see if a finger on the platter will stall it. If it doesn’t stall but does in transition mode then it must be the cam gear.
John.

[John10b]

You have been given all the right advice I’m sure you’ll fix it with plenty of patience. The comment about kinetic Energy is a very valid observation, and so cleaning off old grease and carefully using lubricants to ensure perfect movements on all parts is of paramount importance.
just to add my own comments.This is a common problem and I’ve overcome it by removing the idler wheel and spinning it in a drill and very carefully skim the edge using fine sandpaper.
In previous threads I’ve asked about how to measure the torque on this type of motor but didn’t get a conclusive answer.
Cheers
John

[julie_m]

Note that skimming down the idler wheel will not affect the turntable speed! For every metre travelled by a point on the motor spindle, a point on the turntable rim will move one metre, regardless the size of the intermediate wheel -- and we don't care how many turns that makes.

To measure the motor torque, you would have to attach a wheel to the motor spindle and connect a thread wrapped around the wheel to a spring balance. Note the reading on the balance when the motor stalls, and switch off quickly to avoid damaging the motor. The torque is then equal to the force in Newtons (= mass reading times g = 9.8m.s-2), times the radius of the wheel in metres.

[John10b]

When I talked about skimming the idler wheel I perhaps should have clarified, it was to stop slipping of the wheel, not to change its speed.
Regarding measurements of torque, yes thank you Julie, that’s understood, I was wondering if there was any data for this type of motor.
All I do is pinch the motor till it stops turning and just try I make a judgment, not very scientific but better than nothing!
Cheers
John

[john.north]

Hello,
Re post 7. The cam is the round cog with teeth on which is driven by the platter.
This needs removing and the grease cleaning off and regreasing. The cam drives the underneath mechanism via a pin which runs in the cam track. Also on top of the cam are two plates which should be free to move. If not clean with isopropyl and clean the pin as well. On some decks these plates can take some shifting.
As for the cam when the circlip is removed if it won’t lift off easily use light heat from a hair drier to melt the old grease and it will come away.
John.

[Station X]

See post #4 in this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=75401

Plenty of pictures of the cam gear there.

[John10b]

Excellent data in post 4, as you said Graham.
Cheers
John

[jackcoom53]

Thank you everyone for your excellent advice. Now that I know what the cam is, there is something there that has me puzzled but I know that I am probably totally and utterly wrong but the workings underneath the cam and in particular the "bit" (sorry but I don't know its correct name for it) that sits in the groove that is underneath, does that have some kind of bearing type of thing on it, does is turn when the cam is moving. My reason for asking is that on some videos that I have seen it does but on mine it is seized solid could this be causing the problem that is if you know what bit I mean. I will try and post a photo of it so you all know what I mean.

[recordplayer]

Hi , make sure there is enough tension on the spring that pulls the idler wheel onto the motor spindle - if it has stretched this will affect the torque - cut some off the old spring or fit a slightly stronger spring - Tony .

[john.north]

As far as I know on bsr decks the pin that fits in the cam groove has a fitting on it that doesn’t move. Make sure the pin and groove has enough grease but not too much. Do not use silicon grease. Also make sure the trip plates on top are free. I don’t think the spring has any effect on the drive. If all the surfaces are good and clean and the idler is touching the motor then there will be enough gription to drive the platter. If it is a ua monarch style the spring tension is on the centre assembly rather than pulling the idler towards the motor. This can be increased by winding round twice from its starting point and hooking over.
John

[jackcoom53]

I hope that this helps! Here is a video of what is happening when I use the autochanger on 33 rpm. Can I just say thank you to everyone for your excellent advice!


https://www.youtube.com/watch?v=vBDVsMzJWT0

Jacky.