Nad 6100 Cassette Deck plays a few seconds just fine then stops

Just a note added, late: I bought a nonworking 6100.  No FF, RR, or play, but seems electrically OK, lights, etc..  After using electronics cleaner spray in the two motors, mechanism, and buttons, then relubricating it, it will smoothly FF and RR.  Play function, like yours, still only clicks a short time via its motor, then all goes quiet.  Additionally, the transport roller+heads are on a moving subchassis; it's supposed to be raised up (by a servo or gear) into contact with the capstan and tape when Play is pressed.  But mine doesn't.

I will replace the flat belt, and try to ensure that the Play contacts are clean.  Once that's been tried, I'll add more to this post.  
Thanks,
Rick

Take a look at the tape counter. Its common (and not saying that this deck was done this way) that if the tape counter stops moving, the machine automatically stops. This is done to prevent it from eating tapes.


The symptom is that of the take up spindle not turning. Its supposed to have a certain amount of torque, if not it won't be able to take up the tape from the capstan. So the machine stops, since quite often the tape counter is belt-driven by the take-up spindle.

The most common reason for this is that the tire on the spindle has hardened. If this is the case, the spindle will have to be removed, which can be a bit tricky. Its likely held in by a tiny circlip. When removing the spindle, keep track of all the tiny nylon washers! There's probably one under the circlip and one or two beneath the spindle.
Replacement tires are available from Russell Industries on the east coast. www.russellind.com  You'll have to dig through their catalog to see if they have one that fits. Good measurements are going to be important if they don't show an exact replacement in their guides. Good Luck!

Progress!  That is, enough progress to be hopeful, but not there yet.  My 6100 deck's no-play problem was due to a loose flat belt on the combined mechanism that provides both play-spindle rotation and roller rack positioning.  I was able to test this via a bit of rubbery subterfuge, which quickly gave out.  At the moment, I've unmounted the tape mechanism loosely to get some leeway to work, but it's still the devil to wind the new belt into place with only two hands.  By tomorrow I should have this running; will report again then.   

Nearly there.  The new belt gets the mechanism working properly.  Belt fitment: between the flywheel hub and the mechanism frame, there's a tiny gap up against a gray nylon "keeper" hub; the hub doesn't connect to the flywheel axle, it just holds it away from the frame.  I could just barely slip the belt thru that gap; then the rest of the belt could slip past the motor hub.  Reversing that let me install the new belt.
However, in "Play" there was an insistent, regular blip-blip-blip sound under the music.  I replaced two of the power supply caps and it went away, so I'll replace all the PS caps, hoping that'll do it. Really, the playback quality is quite good at this point, yay.  

OK, final report on fixing my NAD 6100 cassette deck (from eBay as a Part/Repair Unit).  The problems: no FF/RW/Play, and a repetitive "blipping" sound once Play was working.  
My repairs:

• I used electronics cleaner and lube sprays in the motors, tape path, and behind the button control contacts, plus "working" them through several cycles.  That got the buttons and the FF/RW working.
• Replaced the worn flat belt.  That restored Play function, but playback had an electronic blip noise and lack of clarity.
• Replaced all the caps on the PS board with good Elna and Rubycon caps.  That removed the background "blipping" noises.  I believe it also restored the fidelity of the playback quality.

Auditioning: wow, do I like this deck now.  Having a rock-solid tape mechanism paired with Dolby HX-Pro and Tandberg DynEQ, it offers superb playback quality.  This 6100 has detail retrieval, soundstaging, and tonal fidelity better than any other tape deck I've had.  Again, wow.