401 thump

301, 401, plinths and assorted idler stuff
garyt
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401 thump

Post by garyt » Fri Apr 11, 2008 10:31 pm

I'm hoping someone can point me in the direction of an answer to this query. My 401 has a thump which is audible. The thump occurs once every revolution (regardless of speed). Would I be right in thinking it is something to do with the platter rather than the idler? If the idler had a flat spot, that would be apparent more than once per revolution?
Any advice gratefully received.
Gary

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Post by Darren » Sat Apr 12, 2008 12:06 am

Hi Gary,

Is the platter sitting on the spindle taper properly?

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Post by garyt » Sat Apr 12, 2008 5:11 am

Darren wrote:Hi Gary,

Is the platter sitting on the spindle taper properly?
Darren, it seems to be i.e. it doesn't appear to be out of true, & there is resistance when removing the platter.
Gary

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Post by Lee S » Sat Apr 12, 2008 8:59 am

Hi Gary.

Remove the platter and check the inside rim for any kind of damage, including fractures, corrosion, dirt, flat-spots or eccentricity. Could the platter have been dropped? Has it done this since you had it, or is it a recent occurrence? Could the brake be catching on something maybe?

Is there any visible movement in the platter as it rotates either on the horizontal or vertical plane (i.e., does the gap between platter and chassis alter anywhere when looking from the side or does the platter look as though the rotation is eccentric when viewed from above)?

It might also be worth removing the main bearing from the chassis, stripping it down and examining the innards (good chance to give it a thorough inspection, check the spindle for trueness and lube it all up too).

If it is only making this thumping noise once per revolution regardless of speed, it HAS to be something to do with either the platter, the main bearing or the interface of both.

Good luck,

Cheers
©2018 Lee

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Post by Darren » Sat Apr 12, 2008 10:08 am

Hi Lee, good advice,

A little background...

The bearing has only just left here after being stripped down and checked over. It was found to have exceptionally good bearing sleeves and therefore we advised not to change them. The shaft was in equally good condition.

The only change that was made was fitting a ceramic thrust bearing.

There are only two things that go around with the platter in synchrony, the platter itself and the bearing.

The only other thing I can think of right now is the alignment of the idler wheel. We have seen these off the 90 deg angle due to badly machined idler housing castings in the past. Every so often the idler "jumps" as it turns.

maybe in this case once every revolution? It is usually more often.

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pre65
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Post by pre65 » Sat Apr 12, 2008 10:23 am

What about spinning the platter by hand ?

Unplug the power and use the on switch a bit to disengage the platter brake and see if it makes the thump when the idler is not rubbing on the platter.
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Post by garyt » Sat Apr 12, 2008 10:25 am

Lee S wrote:Hi Gary.

Remove the platter and check the inside rim for any kind of damage, including fractures, corrosion, dirt, flat-spots or eccentricity. Could the platter have been dropped? Has it done this since you had it, or is it a recent occurrence? Could the brake be catching on something maybe?

Is there any visible movement in the platter as it rotates either on the horizontal or vertical plane (i.e., does the gap between platter and chassis alter anywhere when looking from the side or does the platter look as though the rotation is eccentric when viewed from above)?

It might also be worth removing the main bearing from the chassis, stripping it down and examining the innards (good chance to give it a thorough inspection, check the spindle for trueness and lube it all up too).

If it is only making this thumping noise once per revolution regardless of speed, it HAS to be something to do with either the platter, the main bearing or the interface of both.

Good luck,

Cheers
Lee, thanks for the trouble you have taken.
There are some 'dings' inside the platter, but it's hard to tell if any of these are the cause since I don't know where abouts the idler interacts with the platter. Any advice?
There isn't any visible movement in the platter as it's revolving in either plane, so I don't think it's out of true.
As Darren has already responded, the spindle & bearing is just back from Slatedeck after being checked & having the new thrust bearing fitted, so I don't think that's the culprit.
Gary

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Post by garyt » Sat Apr 12, 2008 10:43 am

pre65 wrote:What about spinning the platter by hand ?

Unplug the power and use the on switch a bit to disengage the platter brake and see if it makes the thump when the idler is not rubbing on the platter.
Marcus, the thump before was just audible if I listened close to the deck. I did what you suggested, and it changed from a thump to a ringing, so it seems something, somewhere on the periphery of the platter is hitting on the deck. Any ideas on how to determine where this is happening?
Gary

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Post by pre65 » Sat Apr 12, 2008 11:13 am

Hi-i don't want Darren to take offence on this suggestion but i had a similar problem some time ago with a Lenco idler drive turntable where the bearing thrust washer,for some reason,was thinner than it should be and letting the platter sit a gnats lower than it would normally do.

Might pay you to check there are TOTALLY clean and smooth surfaces between the bearing housing and top plate.
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Post by Darren » Sat Apr 12, 2008 11:31 am

No Offense taken Philip, and a good point too.

Different turntables of the same model can have slight variations and as Philip suggests you may want to check that the platter is indeed high enough.

Gary, can you explaine the dings in the platter a bit more clearly, maybe a picture. If you can't post one here just send it to my email add.

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Post by garyt » Sat Apr 12, 2008 11:53 am

Darren, I will post some photos later. With regard to the platter height, how do I check it is correct?
Gary

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pre65
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Post by pre65 » Sat Apr 12, 2008 12:03 pm

Hi Gary-what part of the country are you ?
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)

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Post by garyt » Sat Apr 12, 2008 12:15 pm

Philip, I'm in Belfast, out on the edge of civilised Europe.

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Post by garyt » Sat Apr 12, 2008 12:21 pm

Darren wrote:No Offense taken Philip, and a good point too.

Different turntables of the same model can have slight variations and as Philip suggests you may want to check that the platter is indeed high enough.

Gary, can you explaine the dings in the platter a bit more clearly, maybe a picture. If you can't post one here just send it to my email add.
Darren, the link is to a couple of photos of the 'dings'. The second is a bit out of focus, but should give some idea.
http://imageupper.com/g/?S060001010I2079991772025928
Gary

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Post by pre65 » Sat Apr 12, 2008 12:35 pm

Hi-if that were mine,i would take a file to those "dinks" (not on the inner edge where the idler runs) and just clean them up.

It may be the "gnats whatsit" that is causing your problem.
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)

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