I hate to typecast myself as the Crazy Capacitor Lady of Doom™ or anything, but it sounds a lot like poorly electrolytic capacitors.
From the description of the symptoms, it sounded as though the power supply had conked out partway through programming the chip; then recovered enough while it was switched off after finishing the first 8KB to get partway into the second half before shutting down again. When you did the fast programming cycle, it managed to stay awake throughout the entire performance, so to speak.
Just the fact that it seemed to last longer each time is a bit encouraging; it suggests capacitors could be reforming after having lain dormant for some years. (The oxide layer can decompose over time, and the capacitor will pass a leakage current -- and so, not charge properly and self-discharge -- until the oxide layer reforms.)
The duff capacitors might even have serendipitously saved your chips, if it was struggling to maintain voltage. If you exceed the PIV of the parasitic diodes in the MOSFETs, they will go constant-voltage and draw a high current. The product of that breakdown voltage and the current -- which will depend on the internal (Thévenin equivalent) resistance of the power supply and the voltage difference from what it would be under no load -- is how many watts are being dissipated as heat in the chip.
An EPROM that has not programmed correctly can usually be re-attempted without erasing it if and only if there are no bits set to 0 that should be 1. (Ones where zeros should be aren't a problem. Erasing a chip sets every bit to 1, and programming sets unwanted 1s to 0. If at every location where the stored byte <> &FF, <stored byte> AND <correct byte> = <correct byte>, then you should be good to go.)
Time to whip the multimeter out and see what's going on with those power supply rails. Maybe even treat yourself to a universal component tester and an ESR meter if you haven't already got such.
As far as the matter of programming ICs expecting different voltages from anything your programmer can deliver goes, try and find a schematic -- with any luck, a simple resistor change will be all that's required.
From the description of the symptoms, it sounded as though the power supply had conked out partway through programming the chip; then recovered enough while it was switched off after finishing the first 8KB to get partway into the second half before shutting down again. When you did the fast programming cycle, it managed to stay awake throughout the entire performance, so to speak.
Just the fact that it seemed to last longer each time is a bit encouraging; it suggests capacitors could be reforming after having lain dormant for some years. (The oxide layer can decompose over time, and the capacitor will pass a leakage current -- and so, not charge properly and self-discharge -- until the oxide layer reforms.)
The duff capacitors might even have serendipitously saved your chips, if it was struggling to maintain voltage. If you exceed the PIV of the parasitic diodes in the MOSFETs, they will go constant-voltage and draw a high current. The product of that breakdown voltage and the current -- which will depend on the internal (Thévenin equivalent) resistance of the power supply and the voltage difference from what it would be under no load -- is how many watts are being dissipated as heat in the chip.
An EPROM that has not programmed correctly can usually be re-attempted without erasing it if and only if there are no bits set to 0 that should be 1. (Ones where zeros should be aren't a problem. Erasing a chip sets every bit to 1, and programming sets unwanted 1s to 0. If at every location where the stored byte <> &FF, <stored byte> AND <correct byte> = <correct byte>, then you should be good to go.)
Time to whip the multimeter out and see what's going on with those power supply rails. Maybe even treat yourself to a universal component tester and an ESR meter if you haven't already got such.
As far as the matter of programming ICs expecting different voltages from anything your programmer can deliver goes, try and find a schematic -- with any luck, a simple resistor change will be all that's required.
Statistics: Posted by julie_m — Sat Nov 30, 2024 12:01 am