Denon DP 47-F does not lock to 33 but locks on 45

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alanmeyne
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Denon DP 47-F does not lock to 33 but locks on 45

Post by alanmeyne » 10 Apr 2019 14:37

Hello, I have recently bought a Denon DP-47 F. The TT does not lock to 33 RPM. if i engage 45 rpm it locks and thereafter go to 33 rpm it locks steady. similarly in 33 rpm, if i assist the platter by spinning it a bit, it locks to 33. though a recap is on the cards, i don't know if that will resolve this...in the service manual it mentions the pulse position adjustment for 33 and 45 rpm. Can the above issue be resolved with some readjustment of the trim pots? Please advise! Thanks.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by lenjack » 10 Apr 2019 16:31

Does the service manual show internal trim pots? If so, you can probably clean them with Deoxit. These Denons were fabulous, but after 35 years of electronically controlled arm and speeds, some of the IC's and capacitors may have drifted out of spec. I don't know if even Denon can fix it if that's the problem.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by alanmeyne » 10 Apr 2019 18:16

Thank you lenjack, I will try the deoxit and the cap change...the manual does show trim pots

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by lenjack » 10 Apr 2019 19:04

Trimpots first. If that works, you may not need to do the caps, unless you want to. I had a dp-52F with external tracking force and antiskate/damping pots, that constantly needing deoxing after 32 years. Never did the caps, but finally sold it, for fear it would eventually get too much to handle.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by alanmeyne » 11 Apr 2019 04:16

Thank you lenjack, will share how that went once i have done that.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by captmark » 11 Apr 2019 08:55

Your issue is most likely a bad resistor R12 if 45 is locked and 33 isn't. The 33 speed is stepped down from 45 by a fixed ratio with that resistor. A recap, though highly recommended will not fix this issue, but will keep 90% of other issues from happening down the short road. You will need an oscilloscope to do the adjustment correctly to get the waveforms right. You can always do it wrong and just turn VR1 to change the 33 speed till you lock and forego 45 locking, but that is a very short term fix. You will need some kind of a stobe disc as doing this will get it to lock to something, but not necessarily 33.3rpm.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by alanmeyne » 11 Apr 2019 17:53

Hi captmark, Really appreciate explaining how the circuit works. Will try to get my hands on an oscilloscope and do the job right as I intent keep this TT for good. Will reach out to you for further guidance...Thank you once again

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by alanmeyne » 27 Apr 2019 07:06

Hi Captmark, I recapped with no resolution (as suspected) to the 33 locking problem... Am trying to understand the circuit. The manual says to adjust VR1 to set the pulse position from TP1 to be at the 50% position of the traingular wave form from TP2 for 45 rpm. This means, there is only one correct physical position for VR1. This is understood. But for adjusting the 33 rpm lock, it says to switch to 33 rpm and do the same, ensuring that the pulse from TP1 is now between 40 to 80% of the wave form from TP2. this may or may not coincide with the 50% position already set for 45 rpm. If VR1 is to be turned to accomplish 33 lock, then it will also mean that the previous adjustment for 45 is upset... your thoughts? Thanks.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by alanmeyne » 27 Apr 2019 07:08

I must confess that i have not checked the health of R12 (22k)...I will do this soon.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by captmark » 28 Apr 2019 05:16

Make sure you have a 60hz strobe disc before proceeding. I am going to guess that R12 is not your culprit, and that you are on the far edge of tolerance (off the 50% center-wave on the 45 rpm reading) so it still locks there yet be too far off to have the quartz circuit compensate on the 33 setting. Before doing any VR-1 adjustments with the scope, check both speeds and make sure you are grounding to the right spot (I don't have the manual in front of me but is specifies the pin on the outside edge of the PCB). You're on the right track and almost have it sussed...

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by alanmeyne » 28 Apr 2019 19:08

That sounds very sensible deduction...Thank you so much captmark. Really appreciate.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by captmark » 29 Apr 2019 08:16

I just realized you may not have 60hz electric where you are-small world! Just make sure you have the right strobe disc for your wall voltage. Good Luck!

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by Rajkumar » 11 Oct 2019 05:18

Hi alanmeyne, do you have any update on this issue, I have same issue 33 flashing, if I switch 45 than 33 it lock. If switch to direct 33 not lock flashing. I have lubricate bearing not help.

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by EdAInWestOC » 31 Oct 2019 13:25

Don't be surprised if the solution to you problem is a full recapping. If your symptoms include a flickering and/or failure to illuminate the Lock indicator then you are likely in need of the recapping.

The circuitry of that table have a number of electrolytic caps which will all be out of spec by now. The fact that it will lock at 45 RPM and not at 33 RPM is just an expression of the state of the caps being out of spec. It just so happens that the circuitry can manage to lock on at 45 RPM but this will fail in the near future too.

Do not over think the issue and do not replace anything until you recap the circuitry. Until then you will not be able to effectively troubleshoot the table.

I have long months of troubleshooting experience with my old DP-62L (now in storage) before I recapped the table. Once the recapping was complete and a pair of traces on the circuit board were repaired my 62L was as reliable as it was when new.

The moral of the story is to recap first and troubleshoot after the recapping is done.

But one word of caution. The traces on the Denon circuit board are subject to lifting off the board if overheated. I have worked with countless circuit boards and the Denon circuit board is the only one I ever had trouble with traces lifting off. BE CAREFUL.

Ed

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Re: Denon DP 47-F does not lock to 33 but locks on 45

Post by rgbit » 25 Nov 2019 17:57

Hi all
My DP-47F have the same symptoms... Does not lock at 33RPM until I left it run some seconds at 45RPM.
I'm a experienced electronic technician, with access to many electronic stuff like oscilloscopes, ERS / capacitor meters, frecuency meters, etc. And really love my DP47F.
I'm investigating this issue from two months. I'm pretty sure that It's not a bad cap problem. I've unsoldered and test all caps from the speed circuit, and all are ok (both capacity and ESR). But anyway I have replaced all of them, without result.
Then I've further read the adjusting procedure on service manual, and done some revision/adjust on all variable resistors from this part of the PCB (motor PCB, and speed / sync circuitry only. I don't touched the tracking /forze circuitry). I have not noticed real improvement after this.
On oscilloscope I could see how the PLL fail sometimes to lock the speed.
Motor circuitry is ok, too.
Magnetic heads on plate appears to be ok too, I could see the correct signals on circuitry with oscilloscope.
I will update this post when find (or not find) a solution. Don't have enough time now...
PD: May be some of you coult try a trick. Move the VR1 variable adjusting resistor a little from actual position to the left or to the right (about 10-20º). This is because the DP speed adjustement procedure use the 45RPM as the "main speed" and 33 RPM is done by a fixed resistor . But all of us need to use it mainly on 33RPM. So changing a little this adjust, may be we could fix the 33RPM, at the cost of 45RPM become more unstable.

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