Hi everyone, with the help of the service manual I found the variable resistor and resistor responsible for speed adjustment. I replaced the fixed 22k resistor (R741) and replaced it with a variable one. Works great BUT : Under a specific setting the motor's speed starts to oscillate and the more I slow the more the speed get unstable resulting in extreme flutter. I tried to find where it was coming from with a scope and it seems that everything is working correctly it's just that the circuit is not tuned for low speed. I'm not understanding the role of every parts of the regulation circuit so I don't know what to do to tune it properly. I tried naively increasing the capacitances around the "servo control", "sample and hold" and "lowpass filter", the system seems to change but still oscillating. Doed anyone would have a clue on how to properly tune the system ? If that's possible at all ? Sorry if you think I should not try to hack such a fine piece of equipement, I'm being very careful haha. Cheers, David
Hi, I may be able to help (no promises!)... I don't know the TC-D5M, but I know a bit about servo control loops and can understand (most of) the schematic. I can't find a datasheet for the CX069 however, so there's a bit of guesswork needed... One thing I can't make sense of is the motor drive stage... there is a pair of wires disappearing off the bottom-right corner of your schematic crop - where do these go? If you can post some scope captures of the waveforms at a few key points then that might also be helpful... Pins 1, 3 and 6 of IC702, and the emitters of Q702 and Q706 would be interesting points to look at.
