Diagnosing and repairing a faulty 64
Posted: Sun May 23, 2021 8:40 pm
My beloved D64 (with Dragonplus) is sick, possibly due to my experiments with my MFM hard disk controller.
On the very day I got my first victory (reading sector 0 from the hard drive), my CocoSDC stopped working reliably, sometimes hanging when I accessed the virtual disks; more often hanging at bootup after Pere's copyright but before Microsoft copyright. I suspected the SD card, and changed it : no improvement !
So I used a plain old DragonDOS controller, with a disk drive and disks that used to work last week and now I have this strange behaviour: when I switch on the Dragon, with the DragonDOS controller plugged in, but the disk drives powered off, I get the correct boot sequence (first Microsoft then DragonDos then OK prompt). But when the drives are powered on, it's about the same as with the CocoSDC, the boot sequence doesn't go through : I get the Microsoft message but the DragonDOS message never appears. It seems to hang there. I suspect interrupts (FIRQ from the DragonDos controller ?). I tried with another DragonDos controller, and the same results. Since I have similar issues with several controllers and the CocoSDC, both with the Race expansion board and without it, there can only be one culprit: my beloved Dragon.
Moreover, pushing RESET with a DragonDos controller and powered up drives results in a frozen Dragon with a chequered display.
Can someone suggest where to look?
On the very day I got my first victory (reading sector 0 from the hard drive), my CocoSDC stopped working reliably, sometimes hanging when I accessed the virtual disks; more often hanging at bootup after Pere's copyright but before Microsoft copyright. I suspected the SD card, and changed it : no improvement !
So I used a plain old DragonDOS controller, with a disk drive and disks that used to work last week and now I have this strange behaviour: when I switch on the Dragon, with the DragonDOS controller plugged in, but the disk drives powered off, I get the correct boot sequence (first Microsoft then DragonDos then OK prompt). But when the drives are powered on, it's about the same as with the CocoSDC, the boot sequence doesn't go through : I get the Microsoft message but the DragonDOS message never appears. It seems to hang there. I suspect interrupts (FIRQ from the DragonDos controller ?). I tried with another DragonDos controller, and the same results. Since I have similar issues with several controllers and the CocoSDC, both with the Race expansion board and without it, there can only be one culprit: my beloved Dragon.
Moreover, pushing RESET with a DragonDos controller and powered up drives results in a frozen Dragon with a chequered display.
Can someone suggest where to look?