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Refurbishing Denon Direct Drive TTs

DangerBoy

DangerBoy

Active Member
Hi,

I've got a few vintage Denon direct drive turntables that I'm going to sell in order to pay for a better model vintage Denon direct drive turntable that I just bought. I'd like to do whatever I can to maximize the value of the ones I'm selling and have noticed some TTs listed as "recapped and refurbished" have done well on eBay. If I could replace a number of old capacitors in the TT for $20- $30 to make it more reliable in the long term and get say $100 more for the TT, I'd be willing to do it.

My question is, what caps should I look at swapping out to increase the long-term reliability of the TT? The motor control unit capacitor? The servo amp unit capacitors? The power supply capacitor? Which caps are the ones that fail most often?

I talked to a local vintage audio shop that refurbishes and services vintage TTs before they resell them and they told me they generally don't like to mess around with any components having to do with the quartz locking speed control if it's working okay already as doing so can create problems that you didn't have before.

What caps would you recommend I swap out if any? What about transistors or resistors?
 
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When I did my Teac, I just replaced all of the electrolytic capacitors. I had no quartz-lock circuitry or ICs to worry about, just analog servo.
 
Some electronica of this vintage have unreliable nla diodes that should be replaced with a double diode combo to prevent failures that might ruin nla chips and other bits.
 
I do not know what your skill level is, but if you are asking this question you will probably end up with a bunch of broken TT. It is not an easy task like changing a bulb.
 
Some direct drives also use transistor types which proved unreliable in the long run. For example Denon DP-3000, the "standard" refurbishment seems to be changing all electrolytics and replacing certain type(s) of transistor with modern equilavent. That said in general with electronics I'm not sure a shot gun approach to maintenance is always a good idea. Certainly if there's a known common component failure, which ends up taking something more important with it as it goes, getting those sorted out is a good idea. If you plan a complete recap of a DD, then at least you should have the service manual handy and be able to perform all adjustment procedures to make sure it operates to spec. Usually you need an oscilloscope for that. If you have one, that probably means you know what you are doing :) The older the DD, the easier to work with they usually are. The aforemention DP-3000 for example is really simple to take apart and work on, and it has a relatively simple circuit. Personally I could take on that one. Some later DDs I probably wouldn't touch myself.
 
I do have an oscilloscope and some skill at soldering but not much experience at refurbishing turntables.

I just have one of the turntables with me right now. It's a DP-1700 with a DP-1000 turntable unit. Having problems finding a (free) service manual or schematic right now... Can anyone help with this?

The others are a DP-55L, a DP-57L and a DP 59L. I have service manuals for the 57L and 59L. Also have one for a 55K which I hope will suffice for the 55L.

What are the types of transistors that are problematic? There appear to be two types on the servo amp board on the DP-1000 Turntable. Some appear to be BJTs and others appear to be FETs. Looks like there are just 7 electrolytic caps on the servo amp board.
 
I applaud the enthusiasm, but fixing a Denon TT is usually not $20-30 in parts; it's first diagnosing the problem, which depending on model will be impossible, then finding parts (yeah some are interchangeable, good luck), third is trying not to screw up something else while your knee deep in the muck (tolerances are ridiculous). There are no "common problematic transistors." All this crap talking in my post and I'm still a fan of Denon TT's! LOL, but I wouldn't buy another if it was anything but free.
 
It would be well to scan the various re-cap/re-furbish posts available on the inter tubes written by some fairly accomplished technicians. Although it may be daunting, you will find that certain discreet circuit boards for controlling, say, the platter functions (on/off, 33/45, speed regulation) are the exact same boards and parts from one turntable to the next in a particular design series. For instance, I think the electronics are much the same in the DP-XF series, with an additional board to detect record size in the fancier models (45f and higher). If you find a tutorial describing how to fix the boards in one of the turntables in your general series, your own model has a very good possibility of having identical parts, problems, and equivalent parts. Some older semiconductors do get noisy or fail for some reason, I've read. It is possible to find equivalent transistors by comparing the specs for those in current production, a skill I have admittedly not attained. Not much you can do about rare or failed ICs though.
 
I don't see any issue with replacing the electrolytic caps if you want to do that, if they're the right values and have appropriate current/voltage ratings you're unlikely to cause a problem, assuming you don't damage anything in the process. Resistors and ICs I'd definitely leave alone unless you're sure they're causing a problem. Resistors*shouldn't* go out of spec unless they've been mistreated somehow. (That said, there are different kinds of resistors with different expected lifespans)

Personally, I think I'd probably do a visual inspection of the caps, check for any performance issues, and if the table is working as it should I'd leave well enough alone. :)
 
Reviving an old thread. I am sitting listening to my DP-3000 which is rock steady speed wise, but only after letting her warm up spinning for 20 mins, otherwise it starts slightly slow then all is good 15 to 20 mins later and it stays good for as long as you listen. What is really odd is leave it for weeks unused as I just did and speed was all over the place. I rechecked the board yesterday, tested the npn transistors, all the caps are already replaced not by me but a messy sod, that is another story.. New caps, no dry joints what the bleep is causing this. Today I am just enjoying listening to it,
next thought is open up the transformer box, wonder if there are any components inside?
The magnetic strip is fine and adjusted correctly, if not it would not work when warmed up.
I got the turntable for free not working after someone had gone nuts with a soldering iron. I managed to reverse his err work..
Wonder if the speed buttons are giving partial connections ie voltage fluctuations?
Maybe a diode now I am thinking about it..
Any thoughts?
Chris
 
Got called out for a job so I did not finish checking, but there is nothing in the transformer box apart a transformer, one thing eliminated. I checked the regs well diodes, they are fine, then got called out. Next plan is to check silicon probably just order what I can as by the time I remove it to test it I may as well replace it.
Any thoughts appreciated what to check first.
Chris
 
Pio1980 said:
Iirc, there's a 9V regulated power source?
Click to expand...
Power supply is regulated, but with diodes. 23v for sure, think there is a 9V too, I have not tested everything yet. So caps are new, npn are good, three pin diodes are good, I have not tested zener's yet or other silicone. I am thinking to order all the silicone as I need to remove it to test it so may as well replace it as I go.
Wonder if a resistor could cause this.. Normally Japanese resistors are reliable though..
Chris
 
I'd suspect the zener in the 9 volt supply, the regular diodes are reliable and don't need routine replacement.
Iirc, this is an AC motor direct drive servo controlled player similar to pre-quartz Sony direct drives, also with rim tach. I think they are technically similar if so, with a solid state "throttle" in the motor AC supply controlled by a servo circuit with rim tach speed feedback. If so, the "standard" reference for the control circuit is the regulated 9 Volt source, and variances there make speed unstable.
It's been a while since I helped someone with one of these AC DD players, I think that one was Sony.
 
Pio1980 said:
I'd suspect the zener in the 9 volt supply, the regular diodes are reliable and don't need routine replacement.
Iirc, this is an AC motor direct drive servo controlled player similar to pre-quartz Sony direct drives, also with rim tach. I think they are technically similar if so, with a solid state "throttle" in the motor AC supply controlled by a servo circuit with rim tach speed feedback. If so, the "standard" reference for the control circuit is the regulated 9 Volt source, and variances there make speed unstable.
It's been a while since I helped someone with one of these AC DD players, I think that one was Sony.
Click to expand...
Thanks for that, really helpful.
I am busy tomorrow, but maybe Wednesday I can have another look and start to check the Zener's
Chris
 
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