Mitsubishi LT-5V

[DigitizerGuy]

LensmanMK2 - I was able to contact the Sansui-Parts site, but they had no information about any of the motors so that seems to be a dead end. I haven't heard from Kraftronic. I sent some questions to DIYHiFiSupply but haven't heard back from them.

[lensmanMK2]

havent heard back either digi, had a look at the associated models for those sansui motors, most seem to be very low end 4 pole motors.. nowhere near the quality of the lt5v

so its looking like diyhifi supply at the moment (or somewhere similar!)

[hunt1990]

any ideas what would cause an lt-5v to loss speed control one Minuit it was great the next it seemed to loss speed control and just go nuts

[DigitizerGuy]

The first thought that comes to mind is that the speed adjustment potentiometers may be dirty. I had this problem (in fact, it was the reason my LT-5V motor wouldn't start). It took a bit of sleuthing with the schematic and a voltmeter to discover this, but I found that the signal to the motor was intermittent and even if it would start, it would often lose speed and stop. The cure was to remove the back cover and the cover over the speed adjustment potentiometers at the left of the turntable when viewed from the front (adjusted by the large wheels protruding through the front panel) and spray electrical contact cleaner (such as DeOxit) into them and turn the wheels through the adjustment range several times to clean them. Also, if they are really dirty, you could just replace them. If I remember correctly, they are 5 KOhm, 5 turn pots.

Good Luck.

DG

[hunt1990]

thanks for the idea but i already used a spare speed init to test that idea is there a senser on the turntable that reads the plater speed as its just that the plater seems to go flat out from start and does not adjust from the speed controls or speed button

[hunt1990]

i put some Vaseline on the tonearm Assembly could this of contaminated the board an made shorts ???

[DigitizerGuy]

There isn't a speed sensor on the platter. The stroboscope markings on the platter are for the user to fine tune the speed using the speed adjustment pots. They aren't used to control the motor speed. The servomotor speed is controlled by a feedback loop involving the motor itself and external wiring from a signal generated by the motor, through the speed adjustment potentiometers, and a switch, then back to the control input of the motor. From your symptoms I would suggest examining the wiring and connectors involved in this. I downloaded the schematic from Vinylengine.com. If you have it, follow the path from the block on the schematic called "T/T Motor" (turntable motor) from the VR terminal (white wire) through connector 6 then connector 4 and the speed adjustment pots (VR103 and VR104), back to the switch (IC 105) then to the master speed adjustment pot (VR105) then finally back through connector 6 to the control input of the motor marked "C" on the schematic (gray wire). If you have a voltmeter you can measure the voltage along that path and see if it disappears at some point. Be careful probing on the circuit board. I use needles attached to my voltmeter probes to minimize size. The connectors are the most likely places for problems to occur due to oxidation of the contacts. The master speed adjustment pot could also be a problem but I'd be careful of trying to clean it. If the adjustment is off, then all speeds will be affected. So in cleaning it, you will change the setting and have to reset it. I haven't found a procedure for adjusting it so if you do so, first be sure to measure the resistance so you can get back to the original adjustment. The problem here is that if the pot is dirty and not making good contact, the resistance you measure will be incorrect. That's why I recommend caution on this pot. If push came to shove, I suppose you could set the speed adjustment pots to the middle of their travel and then adjust VR105 to get the speed within range of VR103 and VR104. If I remember correctly, the voltage in the feedback loop is pretty small - less than a volt or so.

Regarding the Vaseline: I doubt that this is the problem. I don't think Vaseline is conductive. If some did get on the board, I would try to use Q-tips and perhaps some contact cleaner to remove it, but I doubt it is the source of the speed problem.

DG