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Birthday Present! Denon DP-1200

Ok we're back. Got the fuse replaced and with jumpers in place, still have good motion from the spindle. It's jittery and slow, but I'm guessing that has to do with the fact that the magnetic head is getting no input from the platter.

Resistors still heat up significantly, but of course now we know there is something awry in the circuit. :thmbsp:
 
fizzgig said:
Ok we're back. Got the fuse replaced and with jumpers in place, still have good motion from the spindle. It's jittery and slow, but I'm guessing that has to do with the fact that the magnetic head is getting no input from the platter.

Resistors still heat up significantly, but of course now we know there is something awry in the circuit. :thmbsp:
Click to expand...

:banana: :banana:

I know we're probably past this step, but have you checked that the magnetic coating has not been scratched in any way? if it is, the table is toast! I'm not sure it can be repaired at all!
 
jkilla said:
:banana: :banana:

I know we're probably past this step, but have you checked that the magnetic coating has not been scratched in any way? if it is, the table is toast! I'm not sure it can be repaired at all!
Click to expand...

The coating appears to be in perfect condition. We'll see though.
 
I think the motor should run wide-open-fast with the platter off or the diode bridge bypassed, it could run like this if the C20 capacitor was bad or it was wired wrong (which is highly unlikely if the wire color locations match the service manual). I think we could still have 2 problems and I dunno what is going on with the motor, possibly somebody previously ignored the advice to not run it up with the platter off and cooked it. The only good news there is that I suspect all the AC drove models in this class used the same motor making finding a parts donor a possibility if it's bad. Trouble-shooting the control side as we have been doing is difficult without a motor known to be runnable and we have not yet established that condition. Having a platter with a good tach' track coating is a definite bonus regardless.
 
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SOAB! I just read this whole thread hoping to find out what the solution was and no luck yet! I can only imagine how you guys are feeling! Best of luck! :lurk:
 
Plug the motor back into the board as per the manual, carefully jumper just the two diode leads in the center together & briefly power up. If the motor & motor ckt is good the motor should turn smoothly quick-time. If so, we put it all back right and move into the control ckt.

How it should normally work;
The motor will turn the platter at start-up at full power until it reaches a predetermined velocity determined by the speed selection and the tachometer ckt into the control ckt, which uses the transistor across the diode bridge +/- legs as a throttle to control the AC voltage to the motor and set speed. The diode bridge is what makes it possible for a DC bi-polar transistor to control an AC voltage, the rest of the control ckt determines how much & when. With the platter off there is no tach feedback signal to throttle back the power to the motor and it will over-run it's rated speed with excessive sustained applied power.
 
Pio1980 said:
Plug the motor back into the board as per the manual, carefully jumper just the two diode leads in the center together & briefly power up. If the motor & motor ckt is good the motor should turn smoothly quick-time. If so, we put it all back right and move into the control ckt.
Click to expand...

Just to confirm, jumper the two "~" leads on D3. NOT the +/-.
 

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After keeping up with this thread and the new awesome progress that was just accomplished, this deserves a hearty congratulations and a dancing banana!!! :banana:
 
fizzgig said:
Thanks for your help thus far! :thmbsp:
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Bet-cha!:thmbsp:
Next we will check R18 for continuity and TR4 as 2 diodes with the diode checker, base-to-emitter and base-to-collector both directions each, lastly emitter-to-collector both ways. In-circuit with R18 good the last will check as a diode if good because of the bridge.
 
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We're all rooting for you guys, especially those of us who own or have owned an example of this worthy table!
 
Pio1980 said:
Bet-cha!:thmbsp:
Next we will check R18 for continuity and TR4 as 2 diodes with the diode checker, base-to-emitter and base-to-collector both directions each, lastly emitter-to-collector both ways. In-circuit with R18 good the last will check as a diode if good because of the bridge.
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R18 gives me 21.9 both ways when set 200k on the multimeter.

I get NO continuity beep for TR4 on the multimeter no matter what positions the leads are in.

Should I be testing these components out of circuit?
 
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fizzgig said:
R18 gives me 21.9 both ways when set 200k on the multimeter.

I get NO continuity beep for TR4 on the multimeter no matter what positions the leads are in.

Should I be testing these components out of circuit?
Click to expand...

Check TR4 as a diode in diode check mode. R18 should check at ca 1^ (plus the lead resistance) according the the skiz and parts list, set resistance check to lowest range.
 
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