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unclemack

Is there a TT bearing expert in Vic? the Luxman beckons..

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The bearing is not heating up. 

 

It's not heat transfer from the bearing, it's the actual drive chip that is generating the heat and it seems to hit a point there it gets into thermal run-away and then loses the plot.

 

All the control chips have been replaced including the motor drive IC. I've monitored all the power supply rails and can't fault them, I've replaced any of the caps that I suspected might be the cause and the speed control pots have been replaced.

 

I'm not sure that the issue is electronic. Without the platter on, the problem never occurs. Maybe the bearing has more friction than normal, causing excess load on the drive IC? Could be the motor also, but I have had that apart and it looks fine.

 

Of course, you could probably "fix" it by just attaching a big heatsink to the drive IC, although I don't consider that a real fix, as there is some fundamental problem there at needs to be found. 

 

I heated the drive IC up using a hot air gun and a 1" tube (so that only the IC was heated), and the platter spins like crazy instantly. So if we can find what is causing the drive IC to heat up, then we can fix it. Any ideas guys?

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One of those big, passive, heat tube heatsinks like they use on computer chips might be the go.

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A likely candidate that may not have been checked, the speed change relay (I assume that it has one. The cheaper turntables from that era had a mechanical switch but the better ones often used a relay).

Bad speed change relays and speed trim pots are the only components that I have heard of that can make a 'vintage' turntable run 'insanely fast'. It will most likely be near the buttons on the control board. Of course a service manual with a circuit diagram would help a lot but they don't seem to be available anywhere online so it is best guesses from me.

Edited by Telecine

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A likely candidate that may not have been checked, the speed change relay (I assume that it has one. The cheaper turntables from that era had a mechanical switch but the better ones often used a relay).

Bad speed change relays and speed trim pots are the only components that I have heard of that can make a 'vintage' turntable run 'insanely fast'. It will most likely be near the buttons on the control board. Of course a service manual with a circuit diagram would help a lot but they don't seem to be available anywhere online so it is best guesses from 

 

Thanks Stuart for setting me straight. I wrongly interpreted the fault as a bearing issue... Thats what happens when I try to involve myself in matter above my paygrade! :)

 

Telecine, I have a service manual but the site won't let me attach it to this message so if you PM me your email addy, I'll send it to you..

 

Cheers

 

M

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Thanks Stuart for setting me straight. I wrongly interpreted the fault as a bearing issue... Thats what happens when I try to involve myself in matter above my paygrade! :)

 

Telecine, I have a service manual but the site won't let me attach it to this message so if you PM me your email addy, I'll send it to you..

 

Cheers

 

M

PM sent.

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Hi Unclemack,

Nice turntable the Luxman PD 350, too good to scrap.

I'm based in Nowra NSW and can arrange free shipping from Southern Cross and return by coach, Premier Motor Service.

Send it up and I will see what I can do.

Regards,

Vince

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The bearing is not heating up. 

 

It's not heat transfer from the bearing, it's the actual drive chip that is generating the heat and it seems to hit a point there it gets into thermal run-away and then loses the plot.

 

All the control chips have been replaced including the motor drive IC. I've monitored all the power supply rails and can't fault them, I've replaced any of the caps that I suspected might be the cause and the speed control pots have been replaced.

 

I'm not sure that the issue is electronic. Without the platter on, the problem never occurs. Maybe the bearing has more friction than normal, causing excess load on the drive IC? Could be the motor also, but I have had that apart and it looks fine.

 

Of course, you could probably "fix" it by just attaching a big heatsink to the drive IC, although I don't consider that a real fix, as there is some fundamental problem there at needs to be found. 

 

I heated the drive IC up using a hot air gun and a 1" tube (so that only the IC was heated), and the platter spins like crazy instantly. So if we can find what is causing the drive IC to heat up, then we can fix it. Any ideas guys?

 

 

Just throwing ideas around, so please excuse ignorance because its a hard to not see patient and also have no service manual...

 

Its great that we have worked out that increasing the heat on the driver chip increases speed.  So with the belt off the speed stays constant and doesnt increase speed.  Is the bearing easy to dismantle to have the lubricant replaced, just like a LP12 bearing?  If so would you think that replacing the lubricant is considered a possibility of resolving the issue?

 

Im not sure what type of motors that are used on this Luxman, so I cant rule the motor out either. 

 

If lets say the load is causing the motor heat up the driver IC, the motor in most instances will also rise in temp.

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Guest JohnA

Hi Unclemack,

Nice turntable the Luxman PD 350, too good to scrap.

I'm based in Nowra NSW and can arrange free shipping from Southern Cross and return by coach, Premier Motor Service.

Send it up and I will see what I can do.

Regards,

Vince

That is a very nice offer

:thumb:

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That is a very nice offer

:thumb:

Agreed, nice work Vince.

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Hi Unclemack,

Nice turntable the Luxman PD 350, too good to scrap.

I'm based in Nowra NSW and can arrange free shipping from Southern Cross and return by coach, Premier Motor Service.

Send it up and I will see what I can do.

Regards,

Vince

That's very kind Vince. I'll PM you in the coming days to work out how to go about this..

 

Cheers

 

M

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Good on ya, Vince. ;)

 

Stuart seems to have performed some pretty exhaustive diagnostics and pinned the problem down:

 

"It's the actual drive chip that is generating the heat and it seems to hit a point where it gets into thermal run-away and then loses the plot."

 

"Without the platter on, the problem never occurs. Maybe the bearing has more friction than normal, causing excess load on the drive IC?"

 

The only problem about that theory IMO is that UM said the platter would turn at the right speed for several hours ... if there was a "sticking" problem that would generate friction (which, yes, could indeed then cause the drive IC to over-work and get hot) ... then how come this doesn't:

  1. happen for a few hours with the platter on, and
  2. never happens with the platter off?

Stuart said he checked the DC rails - and they didn't vary. :eek:

 

From the above ... maybe (as it never happens with the platter off) there's a wear problem at the bottom of the bearing, caused by the extra weight?  Can you replace the bearing with one of yours?  Failing that, maybe a huge heatsink on the drive IC is the easy solution?

 

 

Good luck,

 

Andy

Edited by andyr

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This is a bit like an episode of House...I love it!

 

Cheers

 

M

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It ain't Lupus.

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I think it was once                  after they said that!

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My money's on the motor being dodgy.

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It speeds up when you heat the chip.........................I'll go with the feedback circuit.

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It speeds up when you heat the chip.........................I'll go with the feedback circuit.

Fair point.

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Hi all,

Let's get it on the bench and go from there, no stabbing in the dark!

And, no promises, but have faith, OA hasen't been beaten yet!

Best to all,

Vince

Edited by Once Analog

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Hey!

No experts!

This is amateur hour!

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Good on ya, Vince. ;)

 

Stuart seems to have performed some pretty exhaustive diagnostics and pinned the problem down:

 

"It's the actual drive chip that is generating the heat and it seems to hit a point where it gets into thermal run-away and then loses the plot."

 

"Without the platter on, the problem never occurs. Maybe the bearing has more friction than normal, causing excess load on the drive IC?"

 

The only problem about that theory IMO is that UM said the platter would turn at the right speed for several hours ... if there was a "sticking" problem that would generate friction (which, yes, could indeed then cause the drive IC to over-work and get hot) ... then how come this doesn't:

  1. happen for a few hours with the platter on, and
  2. never happens with the platter off?

Stuart said he checked the DC rails - and they didn't vary. :eek:

 

From the above ... maybe (as it never happens with the platter off) there's a wear problem at the bottom of the bearing, caused by the extra weight?  Can you replace the bearing with one of yours?  Failing that, maybe a huge heatsink on the drive IC is the easy solution?

 

 

Good luck,

 

Andy

 

A big heatsink would fix it. I'm just not a huge fan of "band aid" solutions  :)

 

Are replacement bearings available for these things? What do they cost? I'd start by swapping it to rule that out. If it still spins out of control, it is probably..... lupas!

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A big heatsink would fix it. I'm just not a huge fan of "band aid" solutions  :)

 

Are replacement bearings available for these things? What do they cost? I'd start by swapping it to rule that out. If it still spins out of control, it is probably..... lupas!

 

Sure, Stuart, the heatsink is a bandaid.  But is an identical bearing available for this late-70s (according to UM) Luxman?  (Unlike LP12s, which are available! ;) )

 

I suspect not ... but if Vince's bearing is not an option (hard to imagine that it will be, as I would've thought platter shaft diameters are unlikely to be identical) then maybe controlling the heat runaway on the drive IC is all you can do?

 

 

Regards,

 

Andy

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Sure, Stuart, the heatsink is a bandaid.  But is an identical bearing available for this late-70s (according to UM) Luxman?  (Unlike LP12s, which are available! ;) )

 

I suspect not ... but if Vince's bearing is not an option (hard to imagine that it will be, as I would've thought platter shaft diameters are unlikely to be identical) then maybe controlling the heat runaway on the drive IC is all you can do?

 

 

Regards,

 

Andy

 

Would the bearing from this be compatible? 

 

http://www.ebay.com.au/itm/Luxman-Turntable-PD-291-Quartz-Direct-Drive-Automatic-/121171578278?pt=LH_DefaultDomain_15&hash=item1c36638da6

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Hi guys, need to have the 350 here to evaluate. Whatever the problem; bearing/spindle, make a duplicate, as good as original!

Belt/lube, my guess not.

The IC very rare, but let's wait and see.

Vince

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