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Old 12th Feb 2017, 1:40 pm   #1
AndrewZ80
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Default Tone arm “kick back” at motor turn off on a BSR HF 100 in a Dansette Minor

Hello all.

We're encountering a problem on a Dansette minor (BSR HF100 turn table) where when the end of record motor turn off mechanism engages the tone arm is kicked back over the last section of the sound bearing groove.

The motor does turn off as expected but clearly this will scratch the records and won’t improve the stylus either. I’ve tried a little lubrication on the friction "elbow" in the linkage between the arm and the latch mechanism but that’s made no difference.

I’ve attached a photo (I hope). The ramp that lifts the latch to turn of the microswitch also has a wedge on it that is design to push the latch arm back. I guess this "resets" the position of the linkage elbow.

Back story: I recently bought the Dansette for my teenage son who's big into collecting old records and nostalgia in general. Because he wanted to use this, and I was worried about the 2 wire mains feed and the effect of using the mono crystal cartridge on his record collection, I’ve replaced the mono crystal cartridge with a BSR SC11M and the original single stage amp with an ECL86 circuit and a decent mains transformer. I’ve also earthed the chassis and the turntable deck.

There is a spring under the arm that seems to control the tracking force. It’s not really adjustable, other than by turning the little wire arm it hooks into. I have made the tracking weigh lighter which seem to have caused the problem but I’m not keen on ruining the records.

Any advice gratefully received. We would like to continue to use this if at all possible.

Thanks.
Andrew
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Old 12th Feb 2017, 2:29 pm   #2
Edward Huggins
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Default Re: Tone arm “kick back” at motor turn off on a BSR HF 100 in a Dansette Minor

The autostop just controls the microswitch (I don't think it retracts the idler) so am surprised that there is such a jolt. Is there much play in the linkage, check all the other associated linkages - there are not many? The heavy tone arm can been tamed by adding weight at the end of the underside of the arm as I have on mine. The ECL86 upgrade is interesting and I bet this sounds good now. Also check the plastic platter has not warped and runs true.
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Old 12th Feb 2017, 3:26 pm   #3
julie_m
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Default Re: Tone arm “kick back” at motor turn off on a BSR HF 100 in a Dansette Minor

The end-of-record trip works using a friction coupling between the tonearm and the trip lever. The idea is that it can transmit enough force from the tonearm to the trip lever to operate the trip mechanism (unless the latter gets pushed back by the protrusion on the turntable hub); but the friction between the two surfaces should be overcome by the force that would be necessary to displace the stylus from the groove.

When the stylus reaches the widely-spaced run-out grooves at the end of the record, the tonearm can move far enough between one "reset" and the next to operate the trip.

It sounds as though the resetting force is somehow managing to couple back through the friction link to the tonearm. Logically that suggests either it is too easy to push the needle out of the groove, or the coupling is transmitting more force than it should be able to.

Is the tracking weight now too low since you fitted the new cartridge? Are the friction surfaces perfectly clean and dry?
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Old 12th Feb 2017, 3:42 pm   #4
Audio1950
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Default Re: Tone arm “kick back” at motor turn off on a BSR HF 100 in a Dansette Minor

As Julie has said, this is a friction link, and as such, no part of it should ever be oiled. When the lever pushed by the arm is hit by the turntable boss, it should slide back, without taking the arm with it. Remove all the linkages, clean off every trace of oil, and reassemble, it should be ok. Unless you have the tracking weight set too low. This deck was designed to track at around the 8-10 gram mark.
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Old 12th Feb 2017, 4:30 pm   #5
Station X
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Default Re: Tone arm “kick back” at motor turn off on a BSR HF 100 in a Dansette Minor

The operation of the velocity trip is explained here:-

https://www.vintage-radio.net/forum/...ead.php?t=8936
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Old 21st Feb 2017, 12:08 am   #6
AndrewZ80
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Default Re: Tone arm “kick back” at motor turn off on a BSR HF 100 in a Dansette Minor

Thanks for the replies folks. I've yet to get back to the Dansette but should do so in the next few days. Hopefully I can report back. I think it's very close to being fully usable.
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