I recently started using a GQ-4×4 EPROM programmer to burn M27C322 and M27C160 UVPROMs for my cartridge projects. The process was long and tedious where it was not supposed to be. The majority of writes to the PROMs resulted in write failures – the host application would report a verify mismatch usually within the first few hundred bytes of the operation. What’s worse is, when I read back the information from the PROMs I did not see the write failures which were reported. A phantom problem – bloody hell!!!
My first instinct was that the ADP-054 16bit adapter I was using in conjuction with the GQ-4×4 had dirty contacts. I cleaned the adapter thoroughly; no effect. I then attempted to clean the GQ-4×4 itself; no effect. Firmware updates, PC reboots, new USB cable, 20 or so different chips; no effect… My GQ-4×4 passed all H/W verification tests from the PC application – what could be wrong?
In deep frustration, I was repeatedly triggering the H/W verification tests from the PC host application, unplugging and re-connecting the USB and power supply cables between every try. On on attempt, I forgot to reconnect the included power supply (12V, 3A) and to my surprise the GQ-4×4 still passed its H/W verification tests and produced all of the necessary high voltages for PROM programming. Hmmm…
I proceeded to attempt to write to a M27C160 with only the USB connected – voilà it works! Can you believe it? Such a simple problem. The included power supply it seems was causing the write failures. Presumably the included 12V 3A power supply is too damn cheap to program PROMs – the onboard voltage boosting circuitry it seems is much more reliable. Without the power supply, I managed to burn several PROMs back-to-back; a feat I had never yet achieved with the included power supply.
I’ve yet to try another power supply in its place, and I may never since it seems to work flawlessly without one. You really think that for an EPROM burner which costs over $100 the manufacturer would at least test it with the actual power supply they are shipping…
Lesson learned – don’t trust included power supplies.