Tektronix XD88 - Part 2

Posted by Maki on Sunday, January 28, 2024

Today I attended a repair workshop at System Source. I brought my XD88 and power supply that I had mostly repaired. I just needed to solder the remaining connections to the regulator. The first half of the repair happened in August 2023, and it’s been sitting on my bench since then. I finally took this oppourtunity to wrap it up. I’m happy to report that the power supply has been restored. I learned that if the fuse is blowing under no load it’s probably the bridge or the MOSFET(thank you Glitch!). Thank you CJ(fellow tek 88k fan) for the fuse.

XD88openwithPowerSupply

Previously, I tried different combination of things to see if I could get serial console working, but was unsuccesful. This time I managed to get the cabling right and the baud rate at 38.4k and confirmed output from the serial port. There’s what’s called a peek-poke motinor on ROM and I was able to read and write data to memory. However the rom didn’t allow me to interactively boot the machine. When I set the dip switches to boot it would only boot and hang looking for the keyboard.

The machine is now ready for a boot image. If you have a boot disk image please let me know(michael dot kato at gmail). Thanks in advance.

firmware version 1.1  Tue Nov 21 10:01:12 PST 1989
printf exception handlers enabled
DISABLING CODE CACHEING
cmmu_cache_clkvr(0xfff04000)
cmmu_cache_ripple(0xfff04000)
cmmu_cache_march(0xfff04000)
cmmu_cache_clkvr(0xfff00000)
cmmu_cache_ripple(0xfff00000)
cmmu_cache_march(0xfff00000)
ENABLING CODE CACHEING
exceptions_tst
   MACC
   IOVF
   PRIV
   SPV128
   DACC(addr=0x3e000000)
   CACC(addr=0x3e000000)
   bitbucket_tsts
pic_tst
SWintr_tst
scan_for_display(0x80020000)-  DISPLAY PRESENT
Display board tests
    CDPs
        Registers
        1-color mode
        2-color mode
        Packed-pixel mode
    Frame Buffer
        2-color mode address walk
        Packed-pixel mode
        Data walk
        Address-at-address
        2-color mode address-at-address
        2-color mode mod-255
        Packed-pixel mode patterns
    RAM DAC
        Registers
        Color pallette ram
        Overlay
    Cursor Controllers
        Registers
        Ram
        Registers
        Ram
    Scroll tests
        2-color Mode Scroll Fill
        1-color Mode Scroll Fill
    VSYNC tests
        VSYNC period= ~16msec
    VCMP tests
    KB/Duart tests
fault: kebyrd_init,  sub-keybrd  FRU-DISP/CE
   timeout waiting for keybrd init