Denon DP1200 Dont start anymore, Help appreciated

[Bidule]

Hello,

I have two old Denon a 110V DP80 and a 220V DP1200.
DP1200 was running fine until recently.
DP80 is running although would need recaping.

I wanted to look if I coulf change the arm on the DP1200, so I opened it from the back side.
Since that, the motor is not spinning anymore.

I have tested the DP1200 motor on the DP80 and it is running, so the motor looks like ok.
I have checked that I have some voltage going to the motor, it looks like so.

Do you have any suggestion ?

 

[tnsilver]

Maybe you've disturbed the end-of-record optical detection sensor at the tonearm base and now the shutter (or even the micro switch) is offset, so the TT 'thinks' it's off. You'll need the service manual.

 

[Bidule]

Thank you Tom,

I've donwloaded the manual.
And to be frank, it's what I was thinking too, some kind of switch that is disabled.
But it doesn't look like so trivial. Anyway, would I have voltage coming at the motor ?
I have tested D4, the 6v zener, there is only 4V3 accross it...
I have tested with ohm-meter TR4, it looks like ok, same for the diode bridge D3

 

[visman]

Isn’t the DP-1200 a fully manual table?

What happens when you power on? Does the strobe light up? Does the 1200 have a fuse?

Check the power switch, check speed switches, when you “opened up the back” did you disconnect or short something by accident?

 

[Bidule]

Hello Visman, thank you for taking care.
Yes, when I power on the strobe lights up. There is a fuse that is fine.
I don't think that I have disconnected anything or shorted something
I have tested Speed Switch and Standby/play swtich, they are ok

 

[tnsilver]

See the SM section about the record-end sensor and the detection circuit plus comment #5 about the reset switch. Try to follow the TA height, record end and spring lever force adj. routines that follow. I don't think this is about component failure. I have a hunch you've upset some adjustment.

 

[Bidule]

Thank you Tom for helping,
I havn't touch the arm, however I have checked again the reset switch and it looks like working fine. If the arm is on rest postion 1, the lever is correctly forced to return to OFF position and the power is not turned on unless I manually keep the lever in the ON position. If the arm is moved on rest position 2, the lever stay in ON position and the power is keeping turned ON (Stroboscope light).
But the motor doesn't spin wathever the Start/STby button position (and the Start/stby switch is working fine).
This indicate that the micro switch is well aligned.
When I manually move the arm toward the end it is properly detected as the power is than OFF.
Although I could go through lead out adjustment, I don't beleive, unfortunately, that it's an adjustment problem. At least, the motor should spin.

 

[Bidule]

I really suspect an electronic problem.
As already mentioned, I have tested D4, the 6v zener, there is only 4V3 accross it, or between (YEL) W-13 and (GREY) W-15.
But worse, I measured only 17V5 while I should have 42V between (ORG) W-14 and (GREY) W-15 with or without the motor connected (CN3).
It looks like there is a problem in the detection circuit.

EDIT:
When the arm is engaged, I get the right volatges 42V and 6V.

 

[Bidule]

I changed C20 3µF/200V with what I had on hand 2,2µF/250V and 4,7µF/630V without succes, Put back the 3µF/200V.

 

[tnsilver]

I wouldn't swap components for no reason. With the arm engaged and the correct 42V and 6V reading - is there any AC voltage going into D3 (1S2372A rectifier bridge)? Is there DC voltage coming out of the rectifier bridge? Is there any AC voltage across that C20 capacitor (yellow/white leads)? How about the other winding (orange/yellow leads)? Careful - These are high voltages!

Are you in Europe or somewhere with a 230V grid? How did you power the 110V DP80 turntable?

 

[Bidule]

Hello Tom,

Yes I'm living in EU. The Denon DP80 has a power transformer front end.

I'll check your points and will report as soon as I have some time availlable.

EDIT:

1. I have 105V AC at the input of D3 (across C25) if, and only if, the motor is plugged in, if not 0 VAC
2. I have 146,3V DC at the output of D3 if, and only if, the motor is plugged in, if not 0 VDC
3. I always have 0V AC across the C20 capacitor (yellow/white leads) (with/wo motor)
4. I have 108V AC at white/orange leads and some AC at yellow/orange leads BUT ONLY Without the Motor. If the motor is connected I get 0V between any leads.

Thank you for your support.

 

[tnsilver]

^ are you performing the measurements with the platter mounted? If not, mount the platter, so the magnetic head gets a reading and kicks in the motor drive circuit - then measure again.

 

[Bidule]

Hello Tom,

The platter wasn't mounted.
I have disconnected the arm sensor unit altogether in order to put everything appart. From what I understand it is just a switch for the solenoid that keeps the main switch on.
I have also bridged the main switch.
So now, if I plug the TT into the mains it should always spin, I have the stoboscope light on.

This time, I have made the measurements with the platter mounted and the Start/Stby switch engaged (Start position = OPEN)

EDIT:

1. I have 110V AC at the input of D3 (across C25) with the motor plugged in.
2. I have 146,3V DC at the output of D3 with the motor plugged in.
3. I still have 0V AC across the C20 capacitor (yellow/white leads).
4. I get 0V between any Motor leads.

Do you think I could plug a tone generator at the head with 555Hz ?
Thanks again for helping
Jean

 

[tnsilver]

at the motor connector, I always read 0V AC from any wires pair.

That's the problem. You should be getting about half mains voltage across C20 (white/yellow). You do have feed voltage across W7/W8 blue wires - right? The start/stand-by switch disconnects the motor drive circuit. Just in case it's faulty, I'd suggest you disconnect it for another test.

Before this test:

• Inspect all the connector wires on all PCB's (all 'W' points), wiggle them a bit, feel for loose contact. Reflow the solder joints with fresh solder for good contact!
  
• Make sure the servo control PCB is grounded properly via the black lead at W16.
• Make sure the transformer is grounded via the green lead.
  
• Open up the speed control knob (on deck) and clean the pot with contact cleaner. Test with an ohm meter to make sure there's no wiper dead spots
• Clean both trimmers on the servo control PCB (where the motor connects). Test with an ohm meter again to make sure there's no dead spots.

When you run this test, if the motor fails to spin - start the platter manually and observe any changes.

Note that if this fails, you're gonna have to check the IC input and regulated voltage pins and after that you're gonna need a scope to verify the waveforms at different points. It's going to get complex.
Is there anything else you remember about how this malfunction started? Did this all begin when you opened up the bottom?

 

[Bidule]

Hello Tom,

To be frank, The TT was running fine the last time i used it, but it was a few month ago. I didn't test it before opening it, so the issue may be something not at all related to the opening.

I have 110V across W7/W8

I have specifically tested the start/stand-by switch and it forms an open circuit, any way I have disconnected it.
W16 isn't anymore conneted to anything as I have disconnected the ARM SENSOR UNIT. Any way I have connected that point to the Earth Ground (Platter support Grounding point)
I have checked both potentiometers, both look fine.

I didn't find any loose wire or bad solder joint.
Nothing change when I move the platter manually, is there a specific place to do measurements ?

 

[Bidule]

Hello Tom,

I have tried with a very old KH Generator that I have (model 5700) at around 550Hz 5mV (difficult to make sure) Sine wave as that is what is shown in the manual at point B (Head connector)
Nothing happened.

 

[tnsilver]

IDK, 5mv seems too low. The SM isn't clear about the magnetic head voltage but after the isolation transformer it looks like there should be a few good volts, so if you're not getting meaningful voltage across C1 - it's not working. If you're spinning the platter manually and not getting some voltage from the magnetic head before T1 and not getting meaningful voltage after T1 - it looks like it's faulty. There's no use debugging the wavefroms of the head amplifier section if it's not getting input from the magnetic head. I thought (hoped) spinning the platter manually will kick start the head amplifier section but it appears that it didn't (faulty magnetic head?).

At this stage it's getting too complex for me to debug from my desk, so I'm just gonna give you a few arbitrary pointers and hope for the best.

• I'd test the 220µF/63 (C19) filter cap and swap it out if it's suspicious and while at it the two 100µF/25V (C7/C16) EC's,
• C13 (0.68µF/50V Tanatalum) to pins 7/8 of the servo control IC plays a role in the precharge circuit and fast motor startup. Test/replace as needed.
  
• The servo control IC input voltage (pin 11) should output a constant (regardless of load) 3V. The operating voltage at pin 15 should be 4.8 - 16V.

I'm suspecting the magnetic head but that's the best I can do from here. These things are complex beasts. Sorry.

 

[Bidule]

Thank you very much Tom.

I'll try a little bit more, if I don't succeed I'll pass it to a lab.

 

[stratokaster]

If it's a standard magnetic tape head, 5mV sounds about right. It really shouldn't produce much more voltage than a magnetic cartridge...

In my experience with Denon DP-2000, which is admittedly not the same turntable but a somewhat similar one, if there's no output from the magnetic head, the motor would run at the runaway speed.

 

[Bidule]

I have also a very old scope that works when it wants to.
I have connected the scope directly to the magnetic head and I got about the same signal (5mV sinusoid) as the one I have sent with the function generator.
At least it means that the head is working as it should.

Tomorrow, I will try to test the different signals.
I hope my scope will work...