RABCO ST-4. Help please.

[Last Jeff]

I'm very late to this thread, but as the owner of three ST-4 tables...
The discussion of the motor being dead or not strong enough sounds like it _could_ be a capacitor issue (obviously not in the case of the slipping pulley). I've solved one of my turntable problems that way and am ordering a cap for one more. Part of the issue is that the cap is not shown on the official schematic, nor on the otherwise very nice schematic from HalfApt, above. In re Sam's comment above, this is not the 100 ohm / 0.1uf that is paralleled to the switch, which is basically there to quell lighting (well, sort of). To answer others' questions, yes, they had (at least) two different motors, as evidenced by dramatically different pulley sizes, the newer being a larger pulley. And clearly they knew that their weak motor / heavy platter combo needed help, thus the ingenious "kick" mentioned by Sam and Nat. BTW, with a bit of initial fiddling, two of the ST-4 tables are now my daily runners. Why the trend to give up on semi-auto is well beyond me. We can make a turntable that sells for tens of thousands of bucks but can't lift the tonearm at the end?

 

[Last Jeff]

I'm very late to this thread, but as the owner of three ST-4 tables...
The discussion of the motor being dead or not strong enough sounds like it _could_ be a capacitor issue (obviously not in the case of the slipping pulley). I've solved one of my turntable problems that way and am ordering a cap for one more. Part of the issue is that the cap is not shown on the official schematic, nor on the otherwise very nice schematic from HalfApt, above. In re Sam's comment above, this is not the 100 ohm / 0.1uf that is paralleled to the switch, which is basically there to quell lighting (well, sort of). To answer others' questions, yes, they had (at least) two different motors, as evidenced by dramatically different pulley sizes, the newer being a larger pulley. And clearly they knew that their weak motor / heavy platter combo needed help, thus the ingenious "kick" mentioned by Sam and Nat. BTW, with a bit of initial fiddling, two of the ST-4 tables are now my daily runners. Why the trend to give up on semi-auto is well beyond me. We can make a turntable that sells for tens of thousands of bucks but can't lift the tonearm at the end?

In reply to myself, my latest ST-4 came to me with a .33uF cap on the synchronous motor. Its performance matched that of a brand new cap, meaning it still had a minor bit of hum. Swapping, I found that a 0.15uF cap runs the motor silently and still starts nicely. I guess I'm recording this here for myself in case I forget in another few years...