Epic Plus programmer @16c770

I have an Epic Plus // port programmer with the ZIF 8 to 40 pin adapter.
Todate it has worked without problem on many different chips from 12c671 to 16C774. But I am trying to program a 16c770 and it will not program. The program voltage comes on and it appears to be working but after programming the chip is still blank. If I change to a different PIC, even with sme settings it programs OK. I have tried different 770 chips and different settings without any luck.
Any ideas would be welcomed

Check the VPP voltage, it must be 'round 13 volt while programming.

I heard that sometime the 5 volt regulator may fail... maybe it's time to change it?

Thanks for the suggestions. I have checked both voltages and they are OK.

mmm, ask to Charles at Melabs, sure he know it better than me
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