Denon DP-23F Troubleshooting

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John Paul
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Denon DP-23F Troubleshooting

Post by John Paul » 08 Feb 2018 01:31

I have a Denon DP-23F that I brought back to full working condition and I thought I would put together a couple common troubleshooting issues with this particular deck in one place. These three problems were not clear to me by reading the manuals.

1-You turn it on and press start and nothing happens.

Assuming you remembered to unlock the arm this can be caused by not balancing the tonearm first. It seems to be a bit of a safeguard for your needle. To balance the tonearm you must turn the machine off, move the arm in the space between the tonearm rest and the platter, and then adjust the counterweight until it floats. Return the arm and that is it. You do not need to adjust the tracking force before you do this and you cannot do it properly with the machine on as the electronic counterweights will be active.


2-How do you check and/or adjust the tracking force.

As the platter must be spinning in order for the electronic tracking to activate this seems to cause a lot of confusion. If you want to just do a quick check you can do that on the deck between the platter and the tonearm rest. You can press the lifter button, manually move the tonearm over the scale which will start the platter spinning, then press the lifter button again to let the needle glide down to the scale. If you want to adjust it or get a reading over the platter you must remove the platter and then find a way to raise your scale to what it would be if the platter, mat, and record were still in place. The rest you would do the same as I stated previously. If adjustments are needed they can be performed by rotating VR5 (It is in a labeled hole under the platter and is detailed in the service manual). Again the machine must be on and the motor spinning in order to have the electronic tracking force active.


3-The platter always spins and/or auto return doesn’t work (or is intermittent).

This deck uses a pair of LED lights, three CDS’s (cadmium sulfide Photoresistor) and a shutter attached to the tonearm to know where it’s located. These CDS’s are sensitive to temperature (which can cause an intermittent issue) and can also go out of spec over time. If you remove the bottom cover of your deck (make sure you remove the headshell and platter before turning it upside down) and turn the machine on you should be able to see two LED’s glowing in shrouds on a circuit board facing another circuit board above it that has three sensors attached along with the wiring for the audio signal. The CDS’s change their resistance depending on how much light they get and this deck is wired so that manafests itself in voltage changes presented to IC 2 on the main board. IC 2 is looking for >2.64v from the sensor. In my case my sensors had gotten out of spec to the point that they were only getting to 2.08v. If you have the service manual, a multimeter, and know how to read a schematic you can test it yourself but just changing them is probably a safe bet. As near as I can tell all three Photoresistors are 5-10KΩ and that worked for me. I just picked mine up in a cheap variety pack off Amazon for a couple bucks. It is worth noting that this system is unrelated to how it finds the start of the record (which is a mechanical not electronic design) and the adjustment for that is outlined in the service manual.


Although it is unrelated to troubleshooting I also replaced the capacitors in mine and found this post very helpful in that regard…
viewtopic.php?t=35176#p277397
I found similar discrepancies between what the service manual listed and what was actually there so I would recommend making a list of what is actually there before placing an order and changing them. Digikey does not stock some of the Panasonic part numbers listed in that post anymore but they had Nichicon substitutions for those that worked well for me.

Clabur
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Re: Denon DP-23F Troubleshooting

Post by Clabur » 08 Feb 2018 04:26

Thanks for great info John. I was actually checking the cds’s on my DP-21F, which looks very similar to the 23F, earlier today. I have this problem: At start up, all functions work. After a while, the autostart only works if I choose the 17 cm size. And after a while the function to return the arm work but it keeps running the platter. Cds 2 and 3 measured very similar but the cds 1 gave quite different readings especially when I tested the dark resistance. For instance when testing in quite dark environment 1.8 MOhm for the cds 2 and 3 but only 0.01 MOhm for the cds 1. I was wondering, when the cds go bad, is it that they don’t give enough resistance in darkness or that they don’t go enough low in resistance when exposed to the LED? For example when your IC 2 only got 2.08 V, was it that the resistors didn’t go high enough in resistance or the opposite? My thought was that if the problem is that they don’t give enough resistance it could be enough to replace the cds1 for now.

John Paul
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Re: Denon DP-23F Troubleshooting

Post by John Paul » 08 Feb 2018 04:39

The CDS have lower resistance determined by how much light they get. The less resistance the higher the voltage gets through. In this case the CDS are not giving a low enough resistance because they have aged and become less sensitive to light. You cannot test the resistance while they are still in circuit as you are measuring more than just the sensors. You also can't test the voltage at the sensors as there is other resistance in the circuit to get it to the voltage the controller chip is looking for and the service manual does not give required voltages at the sensors themselves. You have to check voltages at the controller chip if you want to test it as that is where the listed voltages are.

I would just replace them as they are cheap enough and seem to be a common failure point.

Clabur
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Re: Denon DP-23F Troubleshooting

Post by Clabur » 08 Feb 2018 04:43

Ok sounds good. Good info and advice, thanks.

turtle+42
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Re: Denon DP-23F Troubleshooting

Post by turtle+42 » 14 Jun 2018 13:34

Thank you John Paul for the valuable info! Not too long ago, I picked up a P7f. It played OK but the platter started spinning when powered up and the tone arm did not return at the end of the record. I replaced the cds photoresistors and PRESTO, everything works as it should!
I couldn't find them in small quantities, so ended up buying 120 for $7.99 at Amazon. So, if anyone else needs some, I have a few left over :lol: .

selwyn
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Re: Denon DP-23F Troubleshooting

Post by selwyn » 10 Jul 2018 05:04

I have a similar problem, but fitting new photoresistors didn't Help. The existing ones measure between roughly 4k Ohms light and 5 meg Ohms dark. As far as I can determine from the service manual, pins 26 of both IC1 and IC2 are related to auto stop or end of side, and need to have >2.64 Volts to operate. So the resistance of the photo resistors needs to be low enough when lit to supply this - which it does, I'm measuring between 4 and 5 Volts DC at each pin. In the manual it says pin 26 of IC1 is the start/stop terminal, Start = High, Stop = Low.
Which implies (to me) that a high voltage at that pin means the platter spins, and a low voltage means it stops. So 5 Volts at pin 26 = a spinning platter. It would have to drop below 2.64V for the platter to stop. So the photoresistors need to have a high enough resistance when dark to cause this. Which they seem to - the original ones have around 5 meg Ohms and the replacements have around 10 meg Ohms. I've even soldered 10 meg Ohm resistors in place of the photoresistors and this hasn't stopped the platter. So isn't the problem the opposite of what John Paul says? As the photoresistors age their resistance drops? And that causes the platter to spin and the auto-return not to operate? I'm thinking the issue with my turntable is in either the motor control IC or the arm control IC - I've tested components between the photoresistors and the ICs and can't find any which have drifted or failed. And I've also tried putting black tape over both the LEDs and photoresistors and this has had no effect on the operation (or non-operation) of the tonearm or platter. Perplexing!

John Paul
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Re: Denon DP-23F Troubleshooting

Post by John Paul » 10 Jul 2018 05:13

I don't have the service manual handy but from my recollection the way that it works is that the first CDS is what sets the platter in motion and the platter gets the signal to stop as a function of the speed that the second and third CDS's change value. The stop signal is not when one of pins reach the voltage threshold but rather when there is a rapid shift between the two. In other words it is not looking for the record being at a set position but rather when it hits the lead-out on the record and moves inward rapidly.

selwyn
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Re: Denon DP-23F Troubleshooting

Post by selwyn » 10 Jul 2018 10:15

And, lo and behold, after I shot my mouth off...turns out you were right, John Paul! I tried putting LOWER value resistors in place of CDS02 and - voila! Below about 5.6k Ohms the platter stops, the arm returns (part way, because the photoresistor isn't there), I Help it to the rest and the motor shuts off. Looks like the original photo resistor had lost sensitivity, and the one I replaced it with didn't go down in resistance far enough when exposed to the LED. I held the original photoresistor over the LED, measured the resistance and - 14 and some k Ohms. The replacement was about 10k Ohms. Live and learn!
And, yes, I think you're right about how the photoresistors determine when the record has reached the runout. My understanding of all these things is rudimentary, to say the least...

selwyn
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Re: Denon DP-23F Troubleshooting

Post by selwyn » 16 Jul 2018 13:19

The light dependent resistors I used were GL5516. And the problem is solved...thanks John Paul.

IndigoRock2001
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Re: Denon DP-23F Troubleshooting

Post by IndigoRock2001 » 30 Jul 2018 18:12

John Paul wrote:I don't have the service manual handy but from my recollection the way that it works is that the first CDS is what sets the platter in motion and the platter gets the signal to stop as a function of the speed that the second and third CDS's change value. The stop signal is not when one of pins reach the voltage threshold but rather when there is a rapid shift between the two. In other words it is not looking for the record being at a set position but rather when it hits the lead-out on the record and moves inward rapidly.
I found a great resource at https://www.manualslib.com/ You can do a search for any manual or service manual and read it online of download it for free. Has really helped in the last couple of days.
indi

Mafue
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Re: Denon DP-23F Troubleshooting

Post by Mafue » 12 Nov 2018 17:06

Hi,
maybe somebody could Help me out here...

The platter of my Denon Quartz Dp-23F started some day to spin automatically and the auto-return is permanently activated. So I dropped in this forum and replaced the old CDS's with new ones as recomended above:

Fotowiderstand 5 - 10 kohm
Durchmesser 5 mm
Leistung 250mW

Light Resistance 10 lux 5 - 10 kOhm
Dark Resistance 0 lux 0.2 MOhm
Gamma Value 100 - 10 lux 0.6

Power Dissipation 25°C 150 V DC max 300 V DC
Spectral Response Peak 25°C 560 nm
Temperature Range -30 to +70 °

But this hasn't fixed the issue. Maybe I used the wrong CDS's? The old CD1 was dead, I couldn't measure any resistance. After I changed all CDS's I had a level of 8.36 - 8.38 kOhm at all 3 CDS's when the LED's are on.

Has anybody an idea what I can do next?

Thanks for reading and please excuse my bad english.

John Paul
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Re: Denon DP-23F Troubleshooting

Post by John Paul » 12 Nov 2018 18:28

Are the LED's lit up? They might have dimmed over time as well. If you are working on it somewhere the temperature is particularly hot or cold that can affect it as well as the CDS's are kind of sensitive to that. Otherwise you pretty much have to dig up the service manual and probe voltages with a meter.

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