2. analog
  3. 1430204776

JVC TT-101 Won't Stop

The Stop button on my recently purchased QL-10 doesn't work. It worked at first after the TT warmed up, but then quit completely. I since have replaced all 37 electrolytic caps on 3 boards, but it made no difference. The power voltages are correct. The button itself is fine and shorts pins 6 and 9 of the P8 connector on the main board, but the motor doesn't stop. What could be wrong? Any particular transistor or adjustment? Please help! -Alex
safesphere
safesphere OP
2 posts
 
I have measured the voltages on some transistors at different speeds. I can see that pushing the Stop button triggers the following sequence of transistors (per the circuit diagram on page 38 or 39 of the service manual): 629 through 626 and 624, but not 625. The voltages on 625 are off, the same at any speed (12V on C or E and 11.3V on B), and don't depend on VR646. The voltage on the other side of R650 is 0.6V. This makes me think that X625 is gone and needs to be replaced, but I'm not an expert and would appreciate if someone could please confirm my conclusion. Thanks! -Alex
totem395
390 posts
 
Just note that likely you need a set of probes for the suggested oscilloscope.
lewm
13,169 posts
 
Safesphere, Wish I could help, but you've already gone further than I in parsing out that circuit. Early on in the repair of my unit, I gave it to a very competent pro who found no issues with the ICs or the discrete transistors, after he replaced all the electrolytic capacitors. I own a 'scope but have never applied it to repairing the TT101, because the problem is very intermittent and elusive in the first place.
totem395
390 posts
 
If you are not already seeking help elsewhere,you may find a teck hanging out on Audiokarma or diyaudio.
lewm
13,169 posts
 
Safesphere, I am bumping your thread. I did some re-wiring on my TT101 over the weekend, also found a bad electrolytic capacitor on one of the PCBs that are mounted under the top cover. (This was the only original lytic that we failed to replace on the first go-around, and it's the only lytic to be found under the top cover.) In the process of "improving" the wiring integrity, my other goal, I screwed up something. I need to ask you about the order of the wires in one of the connectors on that board. I hard-soldered them to the male prongs, because the connector was very loose. Now I fear I may have gotten the order incorrect. I will post the parts number for that connector, and maybe you can check yours for a reference. (The wiring is color-coded, as you know.) I turned what was once a rare intermittent problem into a consistent problem. Aaarrrggghhh!!!
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