PSX Modchip Installation Semi-failed... help requested.

[StatiKG4]

So far I have installed about 6 modchips in all different playstation models. Most of them were the old 4 or 5 wire chip, and some where the new 8-wire chip. Recently I attempted to install an 8-wire Stealth chip from consolechips.com in a friend's 7001 PSX model. Two of the solder points were extremely difficult because one of the points was the edge of a chip on board. You probably know what i'm talking about if you installed one of the new stealth chips.
I don't even know if the wires are actually connected (the wire is thicker than the connection point!!!)
Anyway, it turns out that all Original games work fine, with no skipping at all. however, most backups do not play at all (it goes to the white and black screens, and then freezes). But Tenchu on CDR plays with many skipping problems.

Main question: Is this the fault of the mod chip? Should I get a new one?
Does anyone have advice for soldering to these near impossible points?

Thanks alot!