Dragon 32 - CPU and PSU Modifcations and Compatibility

Since the introduction of the Dragon 32 there have been several versions produced of both the Central Processing Unit (CPU_ and the Power Supply Unit (PSU).

Now all versions of the CPU will work with the MK3 PSU; this service sheet identifies which modifications are necessary to implement this.

CPU TYPES

16x16 - Two rows of RAM chips, 1x9 and 1x7

Piggy Back - 6 chips on main board, piggy back board in sockets 1 and 8, 11 chips on piggy back board

Siemens - 1 row of 16 RAM chips, 2 chips per socket (one chip on top of another)

OKI - 8 RAM chips (usually labelled OKI)

PSU TYPES

MK1 - 1286 Modulator

MK2 - 1233 Modulator

MK3 - 1287 Modulator

PSU COMPATABILITY

MK1 PSUs now no longer manufactured.

MK2 PSUs are obsolete and when encountered should always be replaced with MK3 boards.

MK3 PSUs now used for all CPUs.

NOTE: For PAL B computers use a normal 16x16 CPU with a MK3 PSU, the PSU only needs the sound altered from PAL A reception. This is done when PSU is checked and setup at PSU work station.

MK3 PSU with 16x16 CPU

With the 16x16 CPU all mods (except possible add on capacitor to position C58) are completed at time of manufacture. Mods as listed below:-

CPU:

    15K resistor (Brown, Green and Orange) to plate through hole which leads to IC12 PIN 10 (Sony Mod.) or for neatness 
    resistor mat be fitted from C28 negative side to solder plate on IC12 Pin 10 line.
    6.8K resistor (Blue, Grey and Red) from solder pad near C6 to bottom of R6.
    If background lines are prominent, fit 220N capacitor in C58 position (Not done at time of manufacture).
    220R resistor short circuited across R9 (R9 being 270R). Alternatively replace R9 with 120R.

PSU:

    Remove existing 1.2K resistor in position R1 and replace with 330R resistor.
    Remove existing 120K resistor in position R6 and replace with 22K resistor.
    Retune modulator sound core.

MK3 PSU and OKI CPU

CPU:

    15K resistor (Brown, Green and Orange) from Pin 4 IC10 to Pin 10 IC12 (Sony Mod.)
    220N capacitor in position C21.
    Cut resistor R6 and solder single cone wire to cut end, then solder other end of wire to pin 14 IC11.
    150 OHM resistor (Brownm Green and Brown) short circuited over R9.
    Drill back of board to open circuit track.

PSU:

    Remove existing 1.2K resistor in position R1 and replace with 330R resistor.
    Remove existing 120K resistor in position R6 and replace with 22K resistor.
    Retune modulator sound core.

MK3 PSU and PIGGY BACK CPU

CPU:

    15K resistor (Brown, Green and Orange) from Pin 4 IC10 to Pin 10 IC12 (Sony Mod.)
    220N capacitor in position C3
    Cut resistor R6 and solder single cone wire to cut end, then solder other end of wire to pin 14 IC11.
    150 OHM resistor (Brownm Green and Brown) short circuited over R9.
    Drill back of board to open circuit track.

PSU:

    Remove existing 1.2K resistor in position R1 and replace with 330R resistor.
    Remove existing 120K resistor in position R6 and replace with 22K resistor.
    Retune modulator sound core.
  

MK3 PSU and SIEMENS CPU

CPU:

    15K resistor (Brown, Green and Orange) from Pin 4 IC10 to IC12 PIN 10 (Sony Mod.) or for neatness resistor may be
    fitted from C28 negative side to solder plate on IC12 Pin 10 line.
    220 OHM resistor short circuited over R9.
    6.8K resistor (Blue, Grey and Red) from bottom of R6 to solder plate near positive side of C28. This resistor needs 
    to be sleeved.

PSU:

    Remove existing 1.2K or 68R resistor in position R1 and replace with 330R resistor.
    Remove existing 120K resistor in position R6 and replace with 22K resistor.
    Retune modulator sound core.