R-83 Popping sound---

[albert]

Albert here in Florida/USA. r83 90% done. I checked mute section and it doesn't seem to cut out completely just lowers. when switch on cam (CS1) turns on or off turntable motor there is a distinct pop from speakers. could the turntable motor be grounding AC in the windings and be bad feeding back to amp AC. Otherwise it spins nicely and to speed. I remove molex to turntable and no pop. while record is playing I can throw CS1 with a mini screwdriver and get it to pop each time I turn the turntable on/off. Mute ckt?? is K1 a relay? cant find it anywhere. Albert

[Ron Rich]

Hi Albert,
"How" did you "check" the mute circuit--Yes"K-1" is a relay, soldered to the amp PCB-- There is generally a two position A-MP plug, hidden under the board, controlling that relay--often it has "fallen off" ( with a "little help" !) Ron Rich

[albert]

yes right now that relay is fed with white/red, orange wires and my meter shows 28vdc and when cs5 triggers to 0vdc so its getting the 28 volts. mute does work. I placed tonearm in up position and ran my finger gently across needle with volume up and no sound. when I select a record and its placed on turntable I run my fingler again and get loud response as it should. only problem is when turntable motor comes on I get a pop through speakers. sometimes loud sometimes soft. so if mute circuit works I believe turntable motor is starting to go bad. even with volume turned all way down I still get mild pops when turntable motor comes on or off. it's like you were playing with the amp power cord pushing it in or out with unit on. that arcing from the ac voltage would cause amp to do a small pop. I think im getting the same reaction from turntable motor. when I disconnect 120vac from the harness I get no popping at all. of course turntable wont spin. I can got record to play (sort of warble if I spin turntable by hand.

[Ron Rich]

Hi Albert,
Got the schematic ?? There should be an "anti-spark (pop ?)" cap somewhere in the power circuit to the motor--perhaps it's bad, or wiggled it's way loose ? If not there, try placing a .01/1400 cap on the controlling switch. Ron Rich

[albert]

yes rich, went over it and saw no caps in that ckt but will check it again. your cap idea is what I was looking for. gonna place one right before turntable 120vac molex plug or maybe right after CS1. that way I can eliminate the spark surge coming from that microswitch.  will keep you posted.

[albert]

Well ron, nothing worked. there is no cap in power supply for 120v volts. BUT, in the amp AC supply there is a .1 400v cap which I isolated and tested with my cap checker and its .106. I just got an extra Mech control unit I repaired. put it in and juke still works perfectly except for turntable motor pop. leaves me to believe its bad. I'm retired due to stroke but was a great amp/tv/appliance tech in NYC in my time. So now my dream of having my own Juke is realized. Appreciate any help as I'm having so much fun here using all my old test equipment.  Al

[Ron Rich]

Hi Al,
I would place that cap on the switch that controls that motor's hot side -- Ron Rich

[albert]

Hot side to ground or hot to cold. I have a .33 400v out of an old power supply. I will try that. but I thought it should be across black to white?

[albert]

what do you think?

if anything it would filter any feedback thru the AC power supply. last I would just change that Cap in amp power supply. I resoldered both ends of it just in case even tho it checked good.

[Ron Rich]

I would not use a .33/400 in place of a .01/1400 ! You could try various combo's across that A-MP, not Molex, plug--won't hurt anything--
Ron Rich

[albert]

ok ron, just so you know the .1/1400 is .1mfd 1400 vdc its equivalent is 450VAC. my .33 is 400 VAC which is equivalent to 1400 VDC. since I'm working with 120VAC the 400VAC is fine. how much filtering I get With a .33 vs .1 remains to be seen. Called NTE and they straightened me out on this.  LOL

[albert]

cant find anything else in my scrap. gonna order one tomorrow.

[Ron Rich]

Albert,
Thanks for the lesson-- --but it's a "point zero one", not ".1". Ron Rich

[albert]

My bad... Cant forget that "0" I know. got a little confused because the cap on the primary for the Amp power supply is a Mylar .1/400vac. With your help I'm going to get this fully working. I just don't want to spend 70 bucks on a used turntable motor only to find that was not the problem or just adding a filter does the trick. see pic of what I'm going to change out first even tho it checked ok. Sometimes they check ok but are bad under load. after 40 years that can happen...LOL

[Ron Rich]

Albert,
NBD--that's a "strange" schematic--it appears that they drew the CB as being "open" ?? I ain't too schmart--but I sure dono how it can work like that ??
Ron Rich