Denon 62L problem

deeply dp
Post Reply
spew2
junior member
junior member
Posts: 5
Joined: 04 May 2017 20:12

Denon 62L problem

Post by spew2 » 05 May 2017 07:20

I have a Denon 62L which I have had for several years. Great turntable. However, recently it started to have speed issues, so based on reading various posts I concluded it needed a recap. I recapped the main board, but when I went to fire it up the turntable failed to maintain a constant speed. After some checking I noticed that I had inadvertently scratched the sensing strip on the inside of the platter. I have found a source for a replacement platter but since then things have gone from bad to worse.

Now the turntable will not run at all. I have checked and rechecked everything and all seems fine. There is power to the deck: the lights all light up. However, when I punch either the 33 or 45 buttons the deck does not spin.

Before purchasing a replacement platter I want to be sure it will work, i.e. there is nothing else wrong with the deck. I would hate to throw more money into a deck that is essentially dead. Is it possible the servo mechanism was almost dead when I did the recap and now has died? Is it possible I screwed up something during the recap? There is nowhere near here than can service these, so that option is out.

EdAInWestOC
long player
long player
United States of America
Posts: 1356
Joined: 03 Feb 2004 01:39
Location: Glen Burine, MD USA
Contact:

Re: Denon 62L problem

Post by EdAInWestOC » 05 May 2017 19:17

It depends on how much experience you have soldering. The Denon PCB traces are subject to separating and you will end up with broken traces if you heated the solder joints for too long. You will have to use a meter to check the continuity of each trace before you know for sure whether this is an issue.

I have many years of soldering experience and I ended up with two places that required repair. I guess I have too heavy a hand when it comes to soldering.

One other thing. You need to pay close attention to the two electrolytic caps that are used as coupling caps for the servo head. IIRC they are C1 and C2 and are 1uF caps. If you replaced them with general purpose caps you will have problems. You need to use good quality audio coupling caps for these two caps.

Ed

spew2
junior member
junior member
Posts: 5
Joined: 04 May 2017 20:12

Re: Denon 62L problem

Post by spew2 » 06 May 2017 06:49

Ed,

Thanks for your reply. I have been soldering and repairing stereo equipment for three decades, working with everything from Litz wire to some fairly tricky board layouts. As for checking the continuity been there done that. Always use audio mode electrolytics.

The fact the deck initially fired up, albeit erratically due to the scratched strip argues the fault was not with the recap. I have the 62L service manual, but unfortunately no oscilloscope to test the main IC. My trouble shooting seems to focus on the following: the motor is dead, the transformer is dead or the IC is dead. The transformer seems to be putting out power so it is unlikely it is the cause. That leaves the motor ad the IC or the defective platter.

EdAInWestOC
long player
long player
United States of America
Posts: 1356
Joined: 03 Feb 2004 01:39
Location: Glen Burine, MD USA
Contact:

Re: Denon 62L problem

Post by EdAInWestOC » 09 May 2017 02:29

spew2 wrote:Ed,

Thanks for your reply. I have been soldering and repairing stereo equipment for three decades, working with everything from Litz wire to some fairly tricky board layouts. As for checking the continuity been there done that. Always use audio mode electrolytics.

The fact the deck initially fired up, albeit erratically due to the scratched strip argues the fault was not with the recap. I have the 62L service manual, but unfortunately no oscilloscope to test the main IC. My trouble shooting seems to focus on the following: the motor is dead, the transformer is dead or the IC is dead. The transformer seems to be putting out power so it is unlikely it is the cause. That leaves the motor ad the IC or the defective platter.
OK...but your logic is a bit faulty.

You are assuming that the motor may be bad. Sorry but that is highly unlikely. Possible, but not the first possibility. The scratch on the platter would not stop the turntable from running. It may lead to intermittent speed control problems but not the symptom you are having.

Maybe I misread what you wrote but your comment that you used all audio type capacitors is a waste. The only place where they are required is for the aforementioned two coupling caps. The rest of the caps are general purpose power type caps.

Since the table had intermittent speed control issues when you began, your conclusion that it needing a recap was probably correct. If your statement "speed issues" means that your 62L was loosing lock and the speed was wavering on playback, yes, that is a symptom that it needed a recap. I had exactly the same issue with my 62L that ran perfectly well since I bought it in 1983.

In spite of your experience it sounds like you have a problem with your recap job. You are erroneously assuming everything is well with the recap job just because it powered up. That is not a symptom everything is well. There are a lot of other potential problems and I say this out of long hours troubleshooting a recap job that I knew was perfectly fine. It wasn't.

The first step in fixing your turntable is to drop the assumption that the recap job was performed flawlessly. Since you started with a speed control issue and now you have another symptom it sounds like you damaged something. I would not look at the motor or the platter as the culprit. It is not likely that suddenly either went bad. Yes, it could happen, but you are reaching here.

Again, I say this out of long hours trouble shooting a turntable that went from a speed control issue to other problems. Just like you are experiencing. My table went from intermittent speed issues to no speed control, to not starting, to no power. All of those problems were caused by my recap job except for the first issue that was caused by old, out of spec caps.

The Denon PCB traces can be very hard to troubleshoot. The worst one I had was the last problem that caused the table to loose power. This was caused by a very small crack on one of the traces in the power supply section of the main PCB. The crack turned out to be where the trace met the soldering pad and it was almost impossible to see, even with magnification.

Checking the continuity was tricky also. When the PCB was unscrewed and I had my meter probes placed on the PCB the traces read OK. When the PCB was put back into the plinth and screwed down the small crack opened up and the trace was no longer good. The Denon circuit board in the DP-62L was one of the hardest I had to troubleshoot in all the years I have worked with my gear.

Before you get back to checking all of the PCB traces I would check all of the cables to make sure everything is plugged back where it belongs. The cables are old too and the connections are one of the first things that can go wrong when you disassemble an old piece of electronics. It is likely that your problem is either with the connections or with one or more broken traces on the circuit board.

Ed

spew2
junior member
junior member
Posts: 5
Joined: 04 May 2017 20:12

Re: Denon 62L problem

Post by spew2 » 29 May 2017 07:36

Your help is much appreciated by those of us working with Denon TT, however for me checking every solder connection is not helpful for trouble shooting. The normal procedure is to seek to isolate the problem in a sector or part then move to looking at the next levels within the faulty sector. With your knowledge of Denon TT you or someone else could be of great help by posting a trouble shooting guide.

To cite one example. As I mentioned the magnetic strip on my platter was inadvertently damaged. How much damage is enough to disable the TT?

As for cap grades, I use what I have in stock.

EdAInWestOC
long player
long player
United States of America
Posts: 1356
Joined: 03 Feb 2004 01:39
Location: Glen Burine, MD USA
Contact:

Re: Denon 62L problem

Post by EdAInWestOC » 07 Jun 2017 20:19

That is a hard question to answer. A single vertical scratch will not pose much of a problem. The servo system can allow for a small interruption of servo feedback. If the scratch is wider or exists along the circumference then you have problems.

The feedback is in the audio frequency range (since the platter does not turn faster than 45 rpm that should not be much of a revelation) and that is why I mentioned about the audio coupling caps from the servo feedback head to the speed control IC. Sorry, off topic.

The servo system relies on the feedback of those pulses to lock onto the speed and keep the platter turning exactly at speed. If the platter servo strip is damaged with a wide vertical scratch it may cause a short loss of servo lock.

You should be able to see it for yourself. You could try marking the outside of the platter with a removable ink marker that notes where the scratch is on the underside and then just observe the lock light and see if you notice any loss of lock.

If you really want to see the extent of the issue hook a dual trace oscope to the test points as described in the service manual and check if the servo system is struggling to keep the lock as the platter turns past the scratchs.

If extreme, it could sound like a belt drive table with a out of round pulley. The servo would loose lock and attempt to compensate. When it looses lock it doesn't immediately go belly up. It sort of cruises for a short period and sees if it can pick up the servo signal again. A LP with piano music is a good test for speed control. the pitch should remain constant and you would be able to hear it with little trouble.

Good luck,
Ed

PS. I recently retired my DP-62L and its back in its box. I bought a new turntable and retired both my Denon DP-62L and my Thorens TD-126IIB w/SME III.

oldguide
member
member
Posts: 28
Joined: 01 Sep 2008 21:00
Location: Minneapolis, MN

Re: Denon 62L problem

Post by oldguide » 22 Jun 2017 23:22

Back again. The platter does not seem to be the problem even with the scratch. I swapped i a platter from another Denon which has a clean magnetic strip and everything is still dead. So having eliminated the platter, where next? I ran a test on the transformer and it seems to be OK. If I read the schematic right the next area to check if both motor and transformer are OK is the servo sector which is on the right side of the main board.

At the moment here is where we are. All lights light up. The lock light flickers. The motor does not run.

Take care and thanks for your patience and help on this.

EdAInWestOC
long player
long player
United States of America
Posts: 1356
Joined: 03 Feb 2004 01:39
Location: Glen Burine, MD USA
Contact:

Re: Denon 62L problem

Post by EdAInWestOC » 12 Jul 2017 04:56

spew2 wrote:I have a Denon 62L which I have had for several years. Great turntable. However, recently it started to have speed issues, so based on reading various posts I concluded it needed a recap. I recapped the main board, but when I went to fire it up the turntable failed to maintain a constant speed. After some checking I noticed that I had inadvertently scratched the sensing strip on the inside of the platter. I have found a source for a replacement platter but since then things have gone from bad to worse.

Now the turntable will not run at all. I have checked and rechecked everything and all seems fine. There is power to the deck: the lights all light up. However, when I punch either the 33 or 45 buttons the deck does not spin.

Before purchasing a replacement platter I want to be sure it will work, i.e. there is nothing else wrong with the deck. I would hate to throw more money into a deck that is essentially dead. Is it possible the servo mechanism was almost dead when I did the recap and now has died? Is it possible I screwed up something during the recap? There is nowhere near here than can service these, so that option is out.
Focus on where all of this started, you had a speed issue. Now you have an issue with the table running at all. It seems pretty obvious that you have an issue with the recap job.

I wish I could be more helpful but there is an issue with something you replaced and soldered. Focus on the circuitry around the speed control IC first. Then carefully inspect the connections to the switches and then to the opto-couplers and the driver transistors. Then check all of the connections from the power supply side of the main PCB.

I would not assume that something is suddenly wrong that didn't have an issue before. It is possible that you have a failure on another component but it isn't likely that something failed along the way. You replaced a number of electrolytic caps and that is where you will very likely find the issue.

If you don't have one make sure you get a magnifying lamp on an articulating arm. You need to inspect traces on the PCB for cracks that could have occurred when you de-soldered the old caps or resoldered the new caps in place. The Denon PCB traces are sensitive to overheating and cracks can form where the traces join the solder pads.

NOTE: The cracks can be very, very hard to see.

This requires that you carefully inspect the traces and a lighted magnifying thing will be very helpful looking for very small cracks in the traces. I had one on the power supply side of the main PCB that drove me crazy. The trace would read fine when the U shaped PCB was unscrewed and when I fastened the PCB back down the crack would open back up.

Don't assume any of your work is fine. Inspect each and every cap for the correct value, type and orientation. If you want that table to work again, you have to treat your recap job as the product of someone else and distrust everything.

Ed

Spinner45
long player
long player
Posts: 2995
Joined: 01 Mar 2017 17:21

Re: Denon 62L problem

Post by Spinner45 » 12 Jul 2017 06:28

Should have taken it to a tech, but I digress.

Post Reply