I have an older GQ-4X (not 4x4) and I never had these issues. I am thinking something changed in the 4x4 version.

I did confirm that the Vpp actually does not touch 25v, but I have not had much trouble and burned probably over a thousand of M2732 ROMs in the last 10 years with that thing. Use the fast speed, double write is on by default. Burns both passes in only like 5-10 seconds. Never had to do multiple burns. Only ones I can remember failing after burn or being unreliable was TMS2732, and I think i just had a bad batch.

Currently go back and forth with a TOP3000 and GQ-4X. Those two burners cover most things up to DIP42. I use the TOP3000 when possible, but it won't do the 24pin ROMs and has a few bad profiles like The 4Mbit EPROM profiles are all screwed up.

Yeah then something has changed in the new 4x4 because I have not seen that behavior. I burn so many chips I would have ran into that. Maybe should stop recommending that burner? Someone should see whats going on the Vpp pin. I'd guess not going high enough V?

I am not sure how well I'd trust a chip that I had to burn a bunch of times to get the write to stick.

1000s of chips on fast no issue with a 10 year old gq4x

speed may be a factor but doesn't seem to be an issue with mine. My TOP3000 programs most chips even faster than the GQ-4X does. W27C512 is 30 seconds GQ4X and 10 seconds TOP3000.

Any alternatives to GQ4x4 that does 24pin 25vpp EPROMs that is win10 compat and not super expensive?

In GQ-4X No VCC control. Speed adjustments are ambiguous, I just leave it wherever the profile is preset too. One thing I have noticed is some chips take longer to program, and if it takes really long I probably selected the wrong profile with too low Vpp. It tells you to use an external power supply, so I always have.

TOP3000 software does not even have a speed adjustment or vcc adjustment. I think it will do a 2716B / 2732B (haven't tried) but no other ones. It has a 25v and 21v profiles, but when you select them the vpp pin stays flat 0v. If it could do the 24pin chips and had a good profile for 27c4001 I would probably retire the GQ4X.