K-Drive has died

[avinunca1]

I've noticed from time a momentary slow down of records and put it down to mains.
Well tonight I was having a very pleasurable listening session when the platter ground to a halt. I am measuring 17 ohms across the pair of wires going to the motor. I can see some 2.6V o/p to the motor regardless of speed switch position except when set to off. I found a BD140 with it's heatsink screw very loose and signs of previous de-soldering. It looks a fairly simple circuit board having a transformer + rectifier cct ,voltage regulator, 3 small sig trannies and two power trannies. The speed indicator led lights and changes colour depending on speed setting.
I suspect the BD140 has overheated but I am wondering about the previous speed dips and wonder if there could be a dry joint. Not sure what else would cause the drops and recoveries. A circuit diagram would be nice though I may be able to figure out the drive circuit. It's all a pain as I have some Graham Slee kit on trial for a fortnight. If anyone knows the normal output voltages it may help me.

[avinunca1]

Didn't want to take the platter off as I find refitting the belt(Vector) a fiddle but did so and the motor is turning and quite strongly. Need to have another look Saturday after a trip to the wool shop.

Now I see I have 2.2V (33rpm) and 2.7 or so (45). Maybe my tapping around the cct did something but the platter didn't move. Will try again while I listen to the motor.I suspect the platter will drive ok unless there's something impeding it's movement.

[natty_dredd]

Need to have another look Saturday after a trip to the wool shop.

Yes, only ever use pink wool or you'll break everything!

Out of interest, is the K-Drive the same as this Vector Drive in the gallery:

[avinunca1]

Mine is Version one with a black control knob, forward mounted led to indicate speed green/red. Mine has a torroidal transformer. Will add a picture if I get time. Very similar. Yes pink wool. Taking no chances.

[willb]

Now I see I have 2.2V (33rpm) and 2.7 or so (45).

Just a thought guys - if 2.7v is right for 45, then 33 should be 2v. Or if 2.2 is correct for 33, then 45 should be nearly 3v, unless AK's done something weird on the new psu's?

Surely the voltage is relative to the speed on dc motors?

[avinunca1]

Don't know enough about motors to say if the v/rpm is linear

[avinunca1]

I am having problems keeping the drive belt on. Need to investigate how I can raise the level of the belt wrt the platter to keep it on. Maybe the belt's a little stretched.

[tim_bissell]

Hmmm, the belt shouldn't fall off easily; the motor and idler pulleys are crowned to centre the belt, and they are all fixed in relation to the platter, unlike the PT1, Too and Export - I would say the belt may well be stretched - it may well be worth contacting Funk and getting a new one ...

-- Tim

[avinunca1]

I removed the deck to a place where I could take a careful look. Couldn't see anything wrong and I managed to refit the belt ok. So far it's been fine though I am keeping an eye/ear open for speed drift with a paper disk. I wonder how the K-Drive compensates for load. It only has two wires going to the motor.
I've realised probably the full potential of the deck this week with the G Slee phono amp set up I loaned from the GS forum. It all sounds very fine indeed.

[natty_dredd]

I think it's called 'current feedback' - I think it responds to the current draw changes caused by eddie currents in the coils opposing motion and how it varies with load. Something like that...

You'll certainly find an explaination on diyaudio.com