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
pbnaudio's avatar
pbnaudio
1,534 posts
 
Here is an excellent oscilloscope for little $

Ebay

Best of luck

Peter
lewm
6,770 posts
 
Unfortunately, the TT101 is very complex. Mine has nearly driven me nuts until I stopped fretting about it (because I realize that I also own 4 other great turntables that perform flawlessly, and it is of little consequence to me if my TT101 is a pain in the ass). Any of the hundreds of solder joints can have gone bad over the 30 or more years since they were built. Re-soldering suspect joints is a place to start. Another occult source of problems is those beige-colored multi-pin connectors. inside those connectors one may have a cracked wire or bad solder joint that is not accessible for inspection. I am about to ditch one of them and just directly solder the wires to the pins in hopes of curing a very elusive intermittent issue I have with mine. I was able to determine that tugging on the harness that goes to that connector can induce the failure mode I am trying to cure.
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
196 posts
 
Just note that likely you need a set of probes for the suggested oscilloscope.
lewm
6,770 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.
More to discover