The Sad Fate of Direct Drive Turntables...

[GordonW]

I've run into several instances where repairing direct-drive turntables has simply not been practical, due to death of the control IC.

The three most common victims, have been JVC, Denon and Dual. I've had models of each, where EVERYTHING right up to the control microprocessor tested good. It's funny... they almost all seem to have the same failure mode- the platter starts to spin up to "warp speed"... instead of 33.33 RPM, it's like several hundred RPM. The motor just goes to max speed, for whatever reason.

And with some of these using what looked to be 30-pin and larger chips... there's a LOT of stuff that would have to be recreated to make it work.

Other problematic tables have been Thorens and Linn, with the servo-generator running their belt-drive motors. Same issues... dead mystery chip, either no motor operation or erratic fits and spurts.

Most of the time, it's a matter of the time and money not being worth the effort... compared to buying the same entire turntable over again...

This is why I'm a big fan of turntables like the AR-XA and such. An AC clock motor, a belt, and a platter. NO WAY that can't be fixed, somehow... and IMHO, they sound better too (less noise).

It's funny, again... how some turntable manufacturers have turned a basic, reliable design into a complicated mess that is virtually un-fixable. This is definitely the case with the later model automatic Thorens models, and any of the more modern Linn turntables. When they went away from synchronous clock motors to complicated DC servos, they lost the dependability that they once had... and IME, they didn't sound any better, either, for the most part, with the DC motors...

Regards,
Gordon.

 

[SaSi]

Just to put things in perspective, isn't all this the reason why many of us procure parts machines?

There have been several threads about fixing units with parts from donor machines including TTs, R2R decks, cassette decks, etc.

I will agree that some TTs make a simple prinicple - perhaps - too complicated. I have a very good example of that. Take a Revox B791 and a Technics SL-1300MkII. Both are direct drive, both have quartz lock, both have push-button operated pitch shift of -9.9 ~ +9.9% and both have a digital readout of speed and pitch.

Now, the Revox has a 10x15cm PCB with discrete TTL ICs (all socketed - thanks Revox) and comes with a Service Manual that apart from schematics, includes a theory of operation section describing how the circuit works.

The Technics comes with a PCB 3 or 4 times the size, several high density ASICs that are a mess to replace - even if replacement chips were available.

Furthermore, on the Revox TT, even the motor can be disassembled to parts and - with due patience - one could even wind new copper wire to the motor if need be. Haven't done that but did succesfully repair a broken servo generator PCB.

 

[interalian]

I'd get a donor for parts if I ever saw one, but the HT-860 is a pretty rare beast. Probably not the LSI at fault, likely just a peripheral transistor failing and driving the LSI into a fail-safe mode. With any luck it can be fixed. Failing that, the Ariston will run until I can afford the VPI TNT (with SME V) a friend is selling. (Yeah, right...)

FWIW, electronics parts have a 'bathtub curve' for failure: high 'infant mortality' rates, a long and low 'in service' failure rate and finally a 'geriatric mortality' rate. That's why manufacturers (used to - now they use statistical models) perform burn-in to get rid of the 'infant mortality', have a nice and long service life and then expect failures well after warranty. 30 years is rather a good run.

 

[shipdriver]

In regards to Victor TTs: I just went through the service manual for the TT-81 and only found one IC which can't be readily or cheaply acquired- there is an IC which has the crystal oscillator with onboard freq dividers, etc. The functional flowchart for that IC is in the manual, so building a discrete replacement is possible (especially when you can narrow it down to only one IC). This is still '70s tech, so it's not like re-engineering a Core i7 CPU. The TT-71 had nothing un-replaceable (the crystal oscillator is a discrete element on the TT-71). Also, I didn't see any special techniques for chip attachment looking at the TT-71 board photo on amp8.com. When I get a chance I'll look at the TT-101 manual.

 

[Brian]

Makes me want to pat myself on the back for having good old fashioned belt drive turntables 2 of which have no variable speed control.

 

[steerpike2]

Makes me want to pat myself on the back for having good old fashioned belt drive turntables 2 of which have no variable speed control.

Although belt drive motor bearings have a limited life. DD bearings are almost indestructable - as are DD motors in theirr entirety.

 

[theophile]

Although belt drive motor bearings have a limited life. DD bearings are almost indestructable - as are DD motors in theirr entirety.

Give yourself a pat on the back there,steerpike.

 

[Stanton681EEES]

Well those of us on this site with Technics 1600 1700 and 1800MKII tables don't have to worry about ICs in our tables as there still made and used today in the Technics 1200 series of tables. Plus the motors are built to run a very long time.

 

[jdwk]

Uhh, let me guess. This purveyor of doom sells new turntables, right? And probably not any of that wimpy DD stuff aimed at the great unwashed. I'm guessing (wait for it) he really likes and sells esoteric belt drive units!

He's absolutely right, though. It's time for all you DD owners to get out while you can. Since I'm such a nice guy, I'll save you from the torment of chip failure by buying your SP-10 Mk II or SP-15. Heck I might even stoop to accepting an SL-1200. Since the chips on these machines are teetering on total destruction and they'll not be good for anything but doorstops thereafter, I can only offer you $50-$75, maybe $100 if in pristine shape.

I can only be so generous so you better act fast.

Actually, its Definitely true of the SP series of turntables. thats why I stopped thinking about putting money into mine. I had two, one worked and the other one needed a chip MN 6042. with out that chip working, the turntable was no good. there are no substitues for this chip and all the other chips that are XX 6042 are not the same chip and will not work. About 20% of the sp series has already developed this problem, even if you find the chips now, lets say you got lucky...they are old too, and may have already failed. this is an age related problem. Technics holds the patent on that chip and will not relaease info on how to manufacture one. Id still have an SP turntable if this werent true. All of the propritary chips for a sl 1200 are still available, and probably will be for some time. I have no belt drive turntables to sell you.

 

[steerpike2]

Technics holds the patent on that chip and will not relaease info on how to manufacture one. Id still have an SP turntable if this werent true.

I don't think anyone would seriously re-manufacture the chips. A single chip costs millions to put into production, and you have to have a big market to make it worthwhile.
But you can clone their function with generic chips like op-amps, comparators, and CMOS logic, or programmable microcontrollers (exactly the project I am working on)
The operational principles of the original chips is no secret.

 

[majick47]

Last week I purchased a Technics SL-1025 (SP-25/SH15-B2 plinth/EPA-250 tonearm). The table is in excellent shape and runs perfect, hopefully since the SP-25 is based on the SL-1200 design parts should be available for quite a while. I have $650 into it which isn't pocket change but at least it isn't up in the thousands if it can't be repaired in the future.

 

[jdwk]

I don't think anyone would seriously re-manufacture the chips. A single chip costs millions to put into production, and you have to have a big market to make it worthwhile.
But you can clone their function with generic chips like op-amps, comparators, and CMOS logic, or programmable microcontrollers (exactly the project I am working on)
The operational principles of the original chips is no secret.

good, when you finish if you perfect one for the technics SP 15 turntable, I will gladly purchase one from you. The SP series was always one of my faves I sold the one I had that still worked so I could get a KAB modded 1200, because I wasnt sure how long the one that worked would keep on working and I needed a new tonarm and did not have the tools to drill out a new armboard for it. But if I replacement for the MN 6042 should ever exist, I may purxhase another SP. I always wanted an SP 10MKIII. Especially with the EPA 500 Arm.

 

[dnewma04]

Actually, its Definitely true of the SP series of turntables. thats why I stopped thinking about putting money into mine. I had two, one worked and the other one needed a chip MN 6042. with out that chip working, the turntable was no good. there are no substitues for this chip and all the other chips that are XX 6042 are not the same chip and will not work. About 20% of the sp series has already developed this problem, even if you find the chips now, lets say you got lucky...they are old too, and may have already failed. this is an age related problem. Technics holds the patent on that chip and will not relaease info on how to manufacture one. Id still have an SP turntable if this werent true. All of the propritary chips for a sl 1200 are still available, and probably will be for some time. I have no belt drive turntables to sell you.

Patents would be expired by now, if there was motivation to create a chip (there wouldn't be), patents wouldn't stop the process.

 

[barkerd]

here's what I don't get : goes right back to the birth of DD's and why I avoided them and their complexity then (and now) ....no knock on anybody who likes them : they just arent my cup.....but to the point at hand : has anybody done a study to see how accurately the average human can (without a side by side reference) detect slight variations in turntable rpm ?
My guess is no human is too incredibly accurate ....MHO of course : but disagree ? SHOW ME THE DATA ... for me personally it comes down to this : the single biggest advantage of DD's (speed accuracy) , for me , is not a measurable and qualified necessity.... the most outrageous TT's I see as audiophile grade are not DD.....not because DD's can't do the job....is the complexity (and as we see now the lifespan) worth the accuracy in the real world?

 

[dnewma04]

Complexity isn't something that is unique to DD. There are equally complex belt drives, as well. I'm also not sure about the comment about outrageous turntables being not DD. Owner's of the SP-10mKIII, the current TOTL Teres, Rockports, and some of the other highend models that have been on the market over the years probably consider their direct drives as good as anything.

 

[JohnVF]

Why does everyone have to generalize everything into camps? Why can't there be good examples of more than one type of drive system? Variety is the spice of life. And it's not too shabby in the music room, either.

 

[Brian]

A motor can be rebuilt, an IC chip can't and if yoou can;t find a replacement chip they motor issue is irrelevant.

 

[BrocLuno]

Back to the OP post - I don't think Tommy should have tossed his defunct DD tables - he should have stuck washing machine (any industrial) motor in there and made stunning DIY RCMs

 

[dnewma04]

John, I agree with you 100%. Everyone may have their favorites and gravitate towards them, but I'd never dismiss a product for falling into a certain category of turntable. When I first got into speaker building, I learned as much as I could, but came to conclusions of what I would consider best and have found over the years that experience works in funny ways. A small amount of experience can form general guidelines for subjective preferences but it can also create biases that are tough to get past. However, as you expand your experiences, and you are lucky enough to keep an open mind, experience almost inevitably leads to the realization that just about every approach has it's own strengths and execution becomes the difference maker. I feel a little sorry for people who decide that past experiences are a reliable predictor of future events rather than a very general guideline as they could be missing out on something special.

Brian, most motors aren't terribly complex devices. Someone who understands circuits and motors should be able to replace an IC with discrete circuitry or replace the entire motor. Whether or not this is worth the expense becomes the question. If I owned an SP-10mkII or mkIII, I'd be very tempted to build a new controller for it. If I had an SL-1200, it just wouldnt be worth it to me since they are still available new.

 

[theophile]

Back to the OP post - I don't think Tommy should have tossed his defunct DD tables - he should have stuck washing machine (any industrial) motor in there and made stunning DIY RCMs

Heck,
For that matter,stick one of the aftermarket idler-drive mechanisms(like VPI's or Teres') up to the platter and use it as an 'idler-drive' turntable.

Run a rubber band onto the rim of the platter and turn it into a 'belt-drive'.

Since these modes of drive are attributed(by their proponents) as being the ne plus ultra ,we DD owners can experience the 'Damasacus' moment of realisation that our beloved DD's idols have clay feet.Aahh the foolishness of our DD ignorance.