I have restored a JVC TT-81 turntable. I was able to obtain the service manual and have adjusted according to the specs. However the electronic brake is over-achieving: Upon pressing the "start/stop" button, the platter stops rotating and then rotates backwards for about 1 revolution.
I've followed the adjustment procedure for VR806 and VR807 but can't correct it. I have not owned a TT81 previously so I'm not sure if this is normal behavior.
I have walked through the troubleshooting checklist for the start/stop. It seems to pass those tests but I assume those are to diagnose a non-functioning system. This one functions, just a bit too well. Also I can't find a copy of the schematics to see if there is a component in the start/stop circuit that needs to be changed.
Any help or suggestions will be appreciated.
I've followed the adjustment procedure for VR806 and VR807 but can't correct it. I have not owned a TT81 previously so I'm not sure if this is normal behavior.
I have walked through the troubleshooting checklist for the start/stop. It seems to pass those tests but I assume those are to diagnose a non-functioning system. This one functions, just a bit too well. Also I can't find a copy of the schematics to see if there is a component in the start/stop circuit that needs to be changed.
Any help or suggestions will be appreciated.
The reverse current supplied when the brake button is pushed is applying too much drive and /or the signal pulse is faulty,look in the --start/stop/motor drive circuit.
Read-3-6 then 3-7 which shows the start/stop circuit especially the reset linked to BJT X825--check capacitor C816-check the "H"/"L" Level -pin 8+pin9 at IC805.
Read-3-6 then 3-7 which shows the start/stop circuit especially the reset linked to BJT X825--check capacitor C816-check the "H"/"L" Level -pin 8+pin9 at IC805.
Thanks, that's helpful. I looked at pin 8 and 9 and they seemed to be functioning OK but I'll take another look and check the reset.
Problem solved. C815 was 33mfd but it should be 3.3mfd. The time to charge this cap controls the reverse current so having a 10x the capacitance kept the reverse current much too long.
In the process I did discover there a couple errors in the service manual. C815 is listed in the BOM section as 33mfd. Fortunately Fig 12 in section 3-9 shows correct value of 3.3mfd. HOWEVER, just to be confusing, Fig 12 lists the cap as "C813" not C815. So a bit of tracing showed that C815 is part of the quick stop circuit, not C813. Then I tried the 3.3mfd value and voila. And fortunately I had some low leakage 3.3mfd caps on hand.
Thanks again for your help. It pointed me in the correct direction.
In the process I did discover there a couple errors in the service manual. C815 is listed in the BOM section as 33mfd. Fortunately Fig 12 in section 3-9 shows correct value of 3.3mfd. HOWEVER, just to be confusing, Fig 12 lists the cap as "C813" not C815. So a bit of tracing showed that C815 is part of the quick stop circuit, not C813. Then I tried the 3.3mfd value and voila. And fortunately I had some low leakage 3.3mfd caps on hand.
Thanks again for your help. It pointed me in the correct direction.