Well considering that Chinese engineers are in Pakistan teaching their Pakistani counterparts how to make the radar, I really don't think there are any black boxes. Especially when Pakistan seems to be integrating indigenous weapons themselves in country without having ship everything to China and getting the Chinese to integrate for them.
As near as I can tell, the co-operative relationship is one based on trust and mutal benefit.
China trusts Pakistan enough to give them full access to anything and everything to do with the JF17 and not worry about Pakistan screwing them over, by leaking sensitive stuff to potential Chinese competitors/enemies. OTOH, Pakistan trusts that China won't leave them flapping no matter what, so are not that bothered about making absolutely every nut and bolt in Pakistan so if something can be made more economically in China, they are happy to do that.
At last , the best explanation came. For friend, China will do almost everything ( remember Korea and Vietnam ).