Modbo 760 & Modbo 4 9xxxx and 79xxx problems

Soldered these two chips to about 5 new consoles. Symptoms are always the same: works just fine when I test it (few reboots, disc swaps). Then customer brings it home and after some time playing, it just stops booting the DVDs. Bootup logo shows fine, but backup copies are not recognized, only originals play.

Soldering is OK, since this happened a few times already. Is there some known incompatibility with these chips on newer PS2's? Consoles are PAL.

Duo3 seems to work OK, but I got plenty of these cheap modbos on stock.

It probably was a wrong "Y" point. I followed a diagram which had it mapped out wrong. But strangely, modchip worked fine even with wrong Y, at least for some time. Console is still in testing, so we'll see if it stops working after some hours/days.

Does anybody know what Y point is for?

check the matrixxxx section for transistor fix

I have used the Modbo 4 sucessfully with the 79000 series but seem to have problems with the 90004. Is this not the right chip for this model or are 5 chips faulty?
Thanks

had the same problem some times ago, it turned out ot be a bad batch of modbo4.0 . replaced with modbo750 it's all good now.