Hey guys I have a strange issue I wonder if you can assist me with.
I made one of the 27c256 based kernal switchers following the guide. At first everything appeared normal but I have actually noticed some bizarre behavior and wonder if it's something i've done wrong. I made the kernal image using the method suggested with both jiffydos and the c64 kernal, and when installed, powering up without RESTORE held down gets me to the JiffyDOS screen perfectly, and everything then on appears great!
If I power up holding down RESTORE, I am presented with the normal C64 BASIC screen (as expected), BUT... when pressing Shift>Run/Stop to load from cassette I get the 'MISSING FILE NAME' error message. If I then disconnect the 1541 it sometimes gives me 'DEVICE NOT PRESENT'. These messages you would usually get in JiffyDOS when using the normal LOAD command (as it defaults to load from disk).
I also then notice that if I try the function keys I am getting garbage characters appearing on the screen. It appears what is happening is that the correct C64 kernal is loading when powering on, but after releasing the RESTORE key, it gets confused and goes half-back to the JiffyDOS kernal.
I then tried manually grounding pin 26 of the EPROM which gets me into the C64 kernal perfectly with everything working as it should - so I am confident that the EPROM is programmed correctly.
It's almost like during the power up and holding RESTORE, that the selected part of the EPROM isn't staying selected (or latching?) and when the key is released it starts accessing the kernal in the wrong place!
Does this ring a bell with anyone? I am wondering if soldering directly to the 74HC74 chip has damaged it some way, could this potentially cause this type of behaviour? (I have actually made another device using the same method, the results are similar).
Sorry for the long post!!!
Kind regards
