I am looking for a circuit of sony single cassete deck tc-k511s

Typically when I need belts for the service business I operate and the unit is a bit strange or esoteric, I send an E mail to Fred Marrs and he comes up with the kit I need. It may not be the cheapest option but it take all the work out of your part of it. If you want to research the belts and order then individually you can save some money but there might be a lot of work involved.
http://marrscommunications.com/sony-belt-kits
Email is [email protected]

Then you should buy some.

Is the tape wrapped around the capstan?

Try
mauritron.com

They have the world's largest library of
owners user instructions operating guides
and
technical repair schematics circuits service manuals

I'm not connected to them, just a satisfied user.
Also if you don't find your item in their listing then ask and they will get it for you

You can download it for free from here:

http://elektrotanya.com/sony_tc-k411_k511s_sm.pdf/download.html

When you use the link you get to a page where you have to wait some minutes to be possible the downloading so please be patient.
Good luck!
Thanks.
gylacz

Depend on your location and willingness to ship the unit. The cost of the repair must also be weighed in. If you don't want to put $100 into it I don't think most shops these days will want to open it up. Dual cassette deck are notorious for failure due to cheap design. Look around at all the problems. I have been fixing units for 40 years and even at Sony and Sony authorized.
I can look at it at Skywave Tape Deck Repair in Chicago area if you want. Google it.

you can not fix it without tearing it apart. if you do take it apart, try to get the front panel off. Hit the eject button and look for a lever that is stuck.

It depend of what you want, where you want use your equipment , and the amplifier have to match your need . This mean , any amplifier can work with your sony.

yes,
check the muting circuit.if cannot fing please mail me i will tell the whicharea.
send the diagram.
to [email protected]