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Old 23rd Apr 2009, 4:15 pm   #1
jimpink
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Default Unreliable auto change mechanism

Hey Guys and Gals,

I have a basic BSR deck which has an unreliable auto change mechanism. Once the record is nearing the end it starts to skip, this is because the auto return is trying to engage but not following through and eventually it jumps back an inch once the record has finished instead of returning to the tone arm stop position.

I've accessed the underneath and it all looks in good condition, no tell tale signs of sticky or hardened grease.

It has worked perfectly in the past but more often than not it does what I described above.

Any ideas?

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Old 23rd Apr 2009, 7:57 pm   #2
Audio1950
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Default Re: Unreliable auto change mechanism

Sounds to me like a sticky trip pawl. Look under the turntable, you will see the main drive cam. Attached to this, and adjacent to the turntable bearing, is a little brass coloured pawl. Take the circlip off, and lift complete pawl off, Clean with alcohol, or at a pinch, WD40, including its mounting spindle, until all old residual oil and grease is removed. Do not under any circumstances re-grease! These things work on metal to metal friction alone. Replace and put the tiniest spot of light oil on its mounting spindle. Should do the trick.
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Old 23rd Apr 2009, 8:39 pm   #3
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Default Re: Unreliable auto change mechanism

If you're unsure about the pawl Barry mentions, have a look at this thread about velocity trips in which post #1 contains a diagram. The thread doesn't specifically cover your deck, but it'll give you the general picture nonetheless.

One other thing; when the tonearm "jumps back an inch", is this by skidding across the record or does the arm actually lift? If assuming it to be the former, this would somewhat confirm a velocity trip problem.
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Old 26th Apr 2009, 4:48 pm   #4
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Default Re: Unreliable auto change mechanism

Sorry for the late reply,

Problem solved, for now. Since I cleaned the trip pawl it worked perfectly but today it started to suffer from the same symptoms but only minor. I feel the problem will return before long and after checking the pawl again I cannot see where that suspect grease is coming from (assuming that's what's making it stick).
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Old 26th Apr 2009, 7:04 pm   #5
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Default Re: Unreliable auto change mechanism

I'm assuming you actually removed the pawl, cleaned it and its spindle then applied a drop of oil as Barry suggested.

How did you actually clean it? A fluid such as IPA or an evaporating spray such as Servisol 'Aeroklene 50' would be best. If the pawl's located by means of a circlip, make sure that's clean too and not bent/damaged in any way that'd allow it to foul the pawl.

Are any of the relevant components made from aluminium or zinc alloy? if so, check carefully for any signs of oxidisation (looks like a white-ish mould). This can cause seizure/partial seizure even with a steel spindle supporting an alloy component.
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Old 30th Apr 2009, 12:57 pm   #6
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Default Re: Unreliable auto change mechanism

I used some WD40 but I think I have some Servisol somewhere. I'll clean it again including the circlip and re-oil, then report back.

Thanks.
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Old 1st May 2009, 10:07 am   #7
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Default Re: Unreliable auto change mechanism

Ok I've cleaned the pawl again this time with Servisol and it seems to be working fine, I'll keep an eye on it though as it's not totally trustworthy yet!

Thanks for all your help!
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Old 1st May 2009, 12:04 pm   #8
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Default Re: Unreliable auto change mechanism

Servisol is not really the type of oil you should be using and you shouldn't be spraying it in liberally which is my understanding of what you've done.

Follow Barry & Darren's suggestions.

You should remove the trip pawl first, these should be NO oil or grease whatsoever just as Barry says, a tiny drop of oil on the pivot.

Unless you service it in the way suggested, it won't be reliable.
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Old 8th May 2009, 1:11 pm   #9
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Default Re: Unreliable auto change mechanism

Yes I did remove the pawl before cleaning and I only used a small amount of the Servisol to clean it.

Since I've done this it is working fine.
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