Denon DP47f problem

[marcbolan666]

Hello DIY, longtime reader, first time poster here:

I've noticed that my Denon DP-47f won't automatically lift and return at the end of specific records.

So far I've noticed this problem on Cowboy Junkies first LP. The Church self titled LP and side 2 of Bob Dylan's Pat Garret and Billy the Kid sound track. Every side of Fleetwood Mac's Tusk. The only consistency I can ascertain is a small run out region between the last track and the label.

No where in any service manual or board have I found an adjustment for this. But most all other records where the tracks aren't crammed almost all the way to the label, the arm lifts and returns just fine. Some thoughts on this would be greatly appreciated!

[wintermute]

Hi Marchbolan666 welcome to diyAudio

I'm uncertain how the mechanism works but I would think that there is a microswitch somewhere. Is it possible that the run out on the records that don't return actually does not go as close to the label as the ones that do? perhaps the arm is just not moving far enough to trigger the microswitch.

The only other thing I could think of is whether it detects the rate of swing of the arm and if the runout is too short it doesn't get the chance, but this seems an overly complex way to do it

Tony.

[marcbolan666]

Tony thanks the reply!

On the records where the needle doesn't lift, the arm goes all the way to the label. On records with a large runout, like the new Beach Boys Smile release, the arms lifts before it has finished the runout groove.

It occurred to me that perhaps it detects the speed change of the arm as it spins off into the runout but like you say, that seems like a crazy way for the thing. I opened her up and looked at the service manual and cannot figure out how end detection is sensed. In my other full auto decks, it is a clear mechanical process. The service manual isn't any clearer. It only suggests that the end detection is handled by the microprocessor. But how does the computer sense the end?

[marcbolan666]

Oh man, look what I found about the dp30l:
The DP-30L (S) turntable also possesses a motor-driven, non-contact optical auto-lift arm mechanism. The end-of-side detector comprises an LED (light emitting diode) and opto-sensor. A shutter is located between the LED and the sensor and moves in accordance with the arm position. When the pickup tracks the run-out groove, the accelerated inward motion produces a sharp increase in the rate of light exposure to the sensor and the lift cycle is triggered.

So if it is the same with the dp47f, how would one calibrate this? Can someone with a dp47 test whether a record with a very short run out works for them?

[wintermute]

Oh man is right, it certainly sounds plausible that it has this optical sensing mechanism and that the short runout isn't enough for it to trigger...

I would think that any adjustment would be in software (unless there is a way to adjust the diode/opto sensor in the arm)

I suspect this was one of those occasions when technology was used for technologies sake. I suppose a diode / opto sensor is probably more reliable than a microswitch, but it's also a lot more complicated

Tony.

[sherpa]

I recommend getting into Vinyl Engine and downloading the service manual, Looks to me there is an adjustment possible but it's based on the start point setting for the stylus.

[pdul]

the optical lense and or mirror probably needs cleaning to increase sensivity. It works every time with my Kenwood, even when I can`t see the dirt

[marcbolan666]

Yes, I've made all the necessary adjustments so that the needle drops at the right spot for both the 12" in 7" sizes but it doesn't seem to affect the end detection. I've scoured through the service manual and there is no mention of an adjustment method.

Now, when I open it up, I can see where the LEDs are that signal the end of the record. How would one suggest I clean the optical sensors safely?

[marcbolan666]

Hey gang I fixed it after breaking it even further! When I opened the beast, I accidentally broke the tracking weight variable resistor right off the board. I soldered a new one on and then went through all the adjustments again. It turns out my vertical lift adjustment was a little off. When I dialed it in, voila, it now lifts at the end of all records despite the runout length.

It always seems I have to make something worse before I can make it work again.

[wintermute]

Good news!!

Tony.