Another eBay "tested" and "working" deck, I take it?
(ie, Not working, laughable pathetic tests.)
An error like this could anywhere.
However, the most likely issue is in the svideo/composite output blocks, or even in the mainboard electronics. The output block is easy enough to fix (on some JVCs), just a swap-out is needed. On other JVCs, resolder work. The mainboard having issues is often a lost cause, as it doesn't really have caps issues (the "easy" fix).
Unlikely heads.
It's not the transport.
If not mere solder work, expect to essentially buy another "for parts" unit (~$200 for this model), or pay somebody to repair it. I might actually be able to repair this, as I have a "for parts" 9911 deck where heads/transport is shot, but mainboard with/and output/input block is assumed fine.
I'm not quite as pessimistic as our friend latreche, but it will require some money + time. Forget about it being cheap or quick, or either.