Question regarding a VCR motor - UK Vintage Radio Repair and Restoration Discussion Forum

Jolly 7 · 24th Jul 2018, 11:04 pm

I have just taken an old VCR to bits and have managed to extract a brushless motor. If I understand correctly, this motor has two sets of coils and each set should be continuous. However, I can only read continuity between the first two connection strips. The 3rd and 4th strip are showing no continuity. Is this indicative of a defective motor ? Pictures attached.

julie_m · 25th Jul 2018, 3:10 am

There are different drive arrangements for brushless motors. There are 8 coils there; but they could be arranged as two groups of four driven both ways (I.e., either end of the coil switchable to either power rail by means of NPN+PNP transistors, or N+P channel MOSFETs), or four pairs driven one way only (I,e., all positives commoned and negatives switched individually, or vice versa). Bipolar drive is electrically more challenging, but gives better torque for the same physical size than unipolar drive. You will need to look more carefully at how the coils are driven. And if in the course of so doing you get an opportunity to probe with your meter, seize it .....

24th Jul 2018, 11:04 pm	#1
Jolly 7 Octode Join Date: Feb 2018 Location: Southampton, Hampshire, UK. Posts: 1,063	Question regarding a VCR motor I have just taken an old VCR to bits and have managed to extract a brushless motor. If I understand correctly, this motor has two sets of coils and each set should be continuous. However, I can only read continuity between the first two connection strips. The 3rd and 4th strip are showing no continuity. Is this indicative of a defective motor ? Pictures attached. Attached Thumbnails Last edited by Jolly 7; 24th Jul 2018 at 11:15 pm.

25th Jul 2018, 3:10 am	#2
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Question regarding a VCR motor There are different drive arrangements for brushless motors. There are 8 coils there; but they could be arranged as two groups of four driven both ways (I.e., either end of the coil switchable to either power rail by means of NPN+PNP transistors, or N+P channel MOSFETs), or four pairs driven one way only (I,e., all positives commoned and negatives switched individually, or vice versa). Bipolar drive is electrically more challenging, but gives better torque for the same physical size than unipolar drive. You will need to look more carefully at how the coils are driven. And if in the course of so doing you get an opportunity to probe with your meter, seize it ..... __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.