Sharp 'Optonica RP114H' belt replacement?

[Refugee]

Is it varying in volume or pitch?
It could be a dried out capacitor that is easy to replace.

[garliccharge]

Is it varying in volume or pitch?
It could be a dried out capacitor that is easy to replace.

Hi
thanks for the quick reply.
its the pitch that changes, not the volume. is that likely to be a cap?

[Yorkie]

I think you need to find out whether it's a problem associated with the amplifier side of things, which would be present if say a 1 KHz test signal a signal was injected into the amplifier, even if the turntable was stationary or if it's caused by the turntable not rotating smoothly. On a conventional turntable, all you'd need to do to check the amplifier would be to lift the tone arm up and inject a signal into the two wires on the cartridge, but of course  with the Optonica, the cartridge is fixed on a linear tracking arrangement, with a cartridge either side of the record so both sides can be consecutively played. There is also LH & RH channels, so one could be faulty, but not the other.

Looking at the scary circuit (from behind the sofa!), on the LH side towards the bottom, above the power supply, you'll see 'Sol 101 & Sol 103' ('sol' presumably meaning solenoid), which I assume to be the pickup. These connect to a plugs and sockets CNS 103/CNP103 (CNS = socket, CNP = plug), and CNS104/CNP104.  On 103 the solenoid is connected to pins 4 & 8, and on 104 to pins 1&2.  Below those plugs/socket, there is CNS105/PL105, which appear to be the LH/RH outputs to your amplifier.

I'd be inclined to unplug the two stylus (styli?) at CNS103/104  and with a record in place and the Optonica  plying (with nothing going from the stlii) inject a sine wave of anything from say 1 kHz to 10 kHz CNP103/CNP104 in turn, and monitor the output at CNS105 for each channel  on a 'scope to see if you get a steady clean sine wave of higher amplitude than at the input. If you do, that suggests that the problem is mechanical due to the turntable not rotating smoothly, which could be the drive motor spindle being partly seized due to dried up grease, or the central spigot on the turntable bearing, or maybe the belt slipping or so such thing.

All of this is of course dependant on having a sine wave oscillator and scope available.

I don't have any expertise or experience of Optonicas beyond fitting a new belt, and all of the above is speculative suggestions  based on looking at the schematic. Certainly you need to determine whether it's a mechanical problem - maybe caused by the turntable not having been used for maybe decades, or electronic. I'm not a betting man, but I'd be more inclined to it being mechanical rather than electronic. The Optonica was way ahead of its time and extremely low wow and flutter were a key feature of its performance.

Can't recall if I posted the schematic before, but if not, I've attached it, along with a clip of the relevant part, with the input & output highlighted.

I hope that helps a bit.

Good luck with it!

[Refugee]

If the pitch is varying it will be mechanical. Perhaps the new belt is too tight so that the motor is struggling.