JVC TT-101 Won't Stop

@lewm   How is it possible to crack the pcb alone?

I think JP would agree that the most likely story is that the crack was there since it left the factory or that the PCB swells and contracts with changes in humidity, thus rendering it susceptible to cracking at areas were expansion and contraction are constrained by the many fasteners that hold the boards in position.  The latter hypothesis is consistent with my observation that it behaved differently (prior to repair) when it sat in our kitchen or a repair shop vs when it was set up in my basement audio system, where temperature is cool and air is moist.

My own TT101 came to me as part of a QL10 (TT101 chassis + plinth + UA7045 tonearm).  The whole thing was "like new" when I bought it, possibly suggesting that it had had a problem from new.  I purchased it very cheaply, described by the seller as "broken", on faith that I could fix it or find someone else to fix it.

@lewm  I have read a lot in the world of the problems that happen to this turntable and I have to note that all problems are the same and similar; maybe you were unlucky with the break of the pcb and I have not read of other cases equal to yours but never other turntables like this have had a lot of problems like the TT-101.
Turntable that sounds good (when it works) but so delicate too delicate and problematic ... it is easy to understand it by reading the defects that happen.

It’s hardly a main stream item anyway, these days or even when it was current.
on the other hand, the TT101 and its ilk are now pushing 40 years old.

On Lew's unit there was a very long scratch under the solder mask.  In this pic you see the very corner of a crack in the solder filet (center) at the ~8 o-clock position.   If you follow the trajectory you can make out the scratch. 

http://fidelisanalog.com/wp-content/uploads/sites/3/2018/12/LM-TT101-Crack1.png

Once the mask was scraped away you can see that the scratch actually cut clean through the trace, and that the little corner of solder which cracked was the only piece making electrical contact.

http://fidelisanalog.com/wp-content/uploads/sites/3/2018/12/LM-TT101-Crack2.png

The boards on these units are very hygroscopic and haven't stood the test of time, nor has the solder.  With the 101 I now vacuum clear every single joint and re-solder fresh.  The riveted vias take a bit of skill as they trap gas and bubble so you have to get the temperatures right and have patience to get a joint that hasn't blown out, and also doesn't have excess solder.

For testing I flex the board approx 30deg in all directions while the unit is running and the drive output is on the scope to see if it causes any glitches.  If it does, which it will, there are still bad joints that need sorted or an issue will develop down the road. 

This is a unit where best practices need adhered to - don't mix old and new alloy, clear all conformal coating to avoid contamination, proper solder filets to prevent pad/trace cracks etc.  

I can refurb 2.5 SP-10MK3 in the time it takes me to do a single TT-101 right.