BIC 980 : Part 2 Turntable strobe/pitch problems!!!

[duncan_england]

Good evening everyone,
A quick catch up on this problem first, or you could read the other thread in this Forum.

I imported a BIC 980 from USA. It had a rough ride in shipping, but I managed to fit it all back together again. She's running fine, with a step down transformer, lovely and smooth and the cartridge and STEREO stylus sound great. I can't wait to fit the Shibata!

The big problem is speed of the platter. The strobe patterns for 33rpm and 45 just will not slow/stop still when you adjust the pitch control:howl.(aaarrgghhh....CD-4 you have got so much to answer for!!). I have also tried altering the coarse pitch control on the Pitch Control Circuit board - with no joy.

Today I fitted a new orange BIC belt and I'm pleased to say it corrected movements through the red guides and now there is a definite speed increase with the platter when I upgear from 33 to 45rpm. (whe - hey....i must be doin' something right!!)

I now firmly believe Doug G is right and that the problem is either the Pitch Control circuit board, or possibly the pitch control knob itself.

Any other ideas, suggestions please guys ?
Thanks Duncan the Brit:chill

 

[Doug G.]

Hi Duncan,

If you are sure there is no interference between the red belt guide (cam) and the belt (is the top of the motor belt pulley even with the top of the red guide?), it does sound like a problem with the motor control board.

It could be the motor but doubtful as it seems to basically work well.

Is there any change at all in the strobe markings when you turn the speed control on top by the platter? Sometimes it is very subtle and you may have to look closely. It is possible for that control to be bad but unlikely.

You said the little bulb on the control board glows evenly and dimly and that is the way it should be. This indicates that the drive signals to the motor coils are equal (there are two separate coils in the motor). It is adjusted by the control that is on the right side of the front of the board. If you turn the control from it present position, the bulb will start to pulse and, eventually, glow brightly but that means the adjustment is way off.

It sounds like it's probably OK but you might want to try and turn the control a bit to see if the bulb actually does start to pulse. You can reset the control so the bulb is steady and dim again. Just don't turn it too far off from where it is now as it will be more difficult to find the correct spot again. It takes very little movement to make a large difference.

The control on the left side of the front of the board is a gain control for the oscillator and feeds back part of the signal from the amplifiers to the oscillator. It's always possible that somebody turned this control and the feedback is not sufficient for the oscillator to work. There really isn't anything to lose if you want to try and turn this control after noting its present physical position so you can set it back if turning it does nothing.

There isn't really any danger of harming anything.

Well, that's it for now. I looked at the spare boards I have and all of them have one or more control covers broken off but I could still send one to you to try to see if it makes any difference.

And it would even be possible for you to send me yours while the one I send you is in your table so you can at least use it and I would see what I can do with yours (if it is, indeed, defective).

Doug

 

[duncan_england]

Doug, Will reply tomorrow... just got timed out replying to you and lost my whole write up!!!
Duncan

 

[duncan_england]

Hi Doug,
Right I've checked the right front wheel on the PC board and yes the bulb almost went out. A further turn and it started to pulsate.

Doug, does your pitch control knob (normal knob on top) have smooth resistance when you turn the knob?i.e do you have to exert pressure with fingers to make an adjustment. Mine is very loose and has lots of play. Underneath the PControl knob I have some rust. Looks like something may have been spilt onto the Pitch Control knob, and run down into the workings and rusted it.
I also think the PC circuit board is possibly ok and that it's the PC knob that could be buggered.

Now that there is no chaffing with the new belt and the cam is working ok, my suspicions are now turning towards the motor. If both 33 and 45 speeds are slow, and the pulley is working ok with a new belt, then the motor must be giving all its got but it's not enough speed.(pre PC Board)

To me the guilty parts are 1) A worn out motor. 2) Pitch control knob broken/rusty.

Does this sound reasonable?
Duncan

 

[Doug G.]

OK, now that you say that about the top panel speed control, it does sound like it may be bad. It should normally turn just like any other control like a volume control or tone control. There shouldn't be a lot of play or looseness. It isn't just that the mounting nut has come loose is it?

Unplug the wires from that control to the PC board and see if the turntable acts exactly the same. If it does, that means the control is open and isn't making any difference even when connected in-circuit. Check out the mounting first, though.

The motor, itself, isn't really pre-PC board but is integral with it and is controlled by it. I doubt it is bad. It's just running slow because the control board is not controlling the speed.

If you could find a control (potentiometer) and wire it in in place of the original suspected speed control, you could verify if that is the problem. It is a 100K ohm pot and, unfortunately, one BIC part I don't have. I will double check, though.

It does sound from your description of the physical operation that it is broken unless the mounting is loose.

Hopefully, that is the problem and relatively easily fixed (if a pot can be found).

Doug

 

[duncan_england]

Ok cheers Doug, having a closer look at the PC tonight.

 

[duncan_england]

Done it Done it Done it Done it Done it Done it !!!!!!!!!!
Doug, I got the 33 strobe to stop!!!!
The normal 33/45 rpm switch on top is miles out. First I adjusted the coarse wheel on the PC board to get it back to it's slowing position then I moved the top surface normal speed change lever to 45 then very very slowly down to 33. At the point where the belt moves position in the cam out of the 45 slot.....The 33 strobe stops but it is so close to between speeds. It is not rubbing either.
Playing well at true 33rpm. I know, I have cheated a bit and that perhaps technically its still not right, but I'm happy. I tried a Beach Boys LP as I know Brian Wilsons voice is high and it sounds quite normal.
Still got a little mains hum though!!!

Next thing is fit the AT cartridge tomorrow.

I am one happy cookie !! Have a good weekend Doug.
Duncan

 

[Doug G.]

Great!

There must still be something goofy with the speed change mechanism and about the only thing it can be if the cam is moving correctly is the height of the motor belt pulley as I mentioned earlier.

If the pulley is too high or low, the cam will move the belt but it won't be where it needs to be on the pulley. That's the fault of the pulley being mispositioned, though, and not the cam.

Doug

 

[duncan_england]

Well the top surface of the pulley is level with it's spindle end - flat level. Both are level with the top edge of the cam guide. I've also squirted some WD40 onto the springs and moving metal parts. I'm happy with it now Doug. You gotta remember its old and didn't cost too much. As long as its working and sounds ok.

Also got an owners manual on order.

I'm getting quite an annoying mains humm through the amp. I presume that the green lead at the back is an earth lead. Can I just patch that onto another appliance's earth terminal Doug?
Dunc

 

[mtgc]

The green lead is earth (what we yanks call ground). I would not connect the green lead to anything other than the amplifier itself, assuming the green lead is coming from the turntable. To connect the ground to another device can develop earth (ground) loops which can really become a problem.

Good luck,

MTGC
Michael

 

[Doug G.]

Ideally, yes, the ground wire should be connected to the amplifier chassis.

But he can try different grounds and it won't hurt anything.

If connecting to a particular ground results in hum, don't leave it there.

I used to have a couple of turntables several feet away from my amplifiers but right near the VCR and DVD player. I connected their grounds to the VCR chassis and everything was hunky dory.

As long as the TT ground is at the same potential as the amp. ground, no hum.

Also, I wrote a reply really early this morning basically saying the same thing but I am currently using an old, slow PC and I left the page before the message was done uploading. Doh!

I'm glad you at least got the speed issue resolved, Duncan, and the ground/hum shouldn't be a big deal.

Hmmm, some day I should hook a generator up to my system so I can hear what 50Hz hum sounds like. \:^)

Once you get the AT cartridge on there, it at least has plastic body mounts so you won't have to worry about ground loops with a metal bodied cartridge.

Doug

 

[duncan_england]

Thanks for that tip Michael. As you know in the UK we have 3 pin sockets with an earthing terminal in the plug. I just wasn't sure and didn't want to blow my house up!!
Have found the ground terminal on my SA 8000X.
Cheers Duncan

 

[duncan_england]

Hi Doug,

Been changing the cartridge this afternoon. My God it's a fiddly thing. The 2 screws that held the AT71E cartridge in the headshell did not fit the AT12Sa !!! So I spent an hour rummaging in the garage to find 2 miniscule Mecanno screws that fitted. Popped on the Shibata and refitted the whole shell onto the arm.
I can see why people use 2 different cartridge shells for quad/stereo now. I think I'll order another shell from Adam in New York. Think I might have to rebalance the tone arm and stylus force as well. Probably tomorrow.
Thats all for today, gotta go out tonight with the wife!!
As usual, thank you Doug for your quality advice.
Duncan

 

[mtgc]

Duncan,

Yes, I have lived in London for several years back in the late 60's, so I am at least passingly familiar with your wiring system. Our modern wiring in the states has a three connector design with the ground being the round terminal at the bottom of the socket and the two other terminals are supply and return, with the return a larger size slot than the supply, this to prevent reverse connections with modern two pin plug designs. Even with our modern wiring system, I am stlll loath to just pick any ground because ground loops can occur between different ground sources due to sometimes very low ohmic resistances between ground sources. I agree with Doug that if the ground causes hum, then move it, but I would still see all the grounds for a particular system taken to the same point.

Good luck with your endeavors and I agree, mounting those cartridges can be a real pain in the posterior.

MTGC (Michael)

 

[duncan_england]

Thanks Michael for your earthing tips. Duncan