Big Book of Amiga Hardware

The GVP Series II HD8+ and HD+ (*) is a high performance SCSI controller and memory expansion for the A500/+.  It connects to the left side expansion slot of the A500/+, and closely matched the case aesthetics. The unit has 4x 30-pin SIMM sockets that can utilize up to four 1Mx8 or two 4Mx8 SIMM modules. A power supply for the GVP unit is required unless an A500 PSU with upgraded 5v/12v ratings is used and modifications to the PCB pads are made.  This unit uses standard 30-pin SIMMs.  It does not use the GVP SIMM32 modules.  Early units may have had labels with 'Impact' on them, but all will have Series II in the name.  The [GVP A530] is a different product, with a 68030 processor, and uses different RAM.

(*) The products are identical/same internals although the product label changed at some point.  They all had Series II identification.  Early models had the old 'Impact' marketing name.

• 2/4/8MB, zero-wait state, FastRAM controller and ANSI XT3T9.2 compatible SCSI interface.
• GVP Dual Port RAM Controller w/High performance DMA transfers to and from hard-disk.
• SCSI raw data transfer rates of up to 3.58MB/sec.
• Auto-configuration for both Fast RAM and SCSI interface.
• Internal 50-pin SCSI connector, External 25-pin SCSI connector (DB25).
• Internal expansion slot for an 80286-based PC emulator card
• FastROM 3.x/4.x, can be disabled with switch for game compatibility. 
• Compatible with GuruROM v6.

Power Connector Pinout:

Looking at the rear of the unit:

   1     3
    4   5
      2

1  Earth Ground
2  Signal Ground (5V ground)
3  +5V RED
4  WHITE (not connected)
5  +12V BROWN

Powering From The Amiga 500

Running the A500 HD8 unit from the original A500 host PSU is not recomended due to the overall power draw (Amps).

Running the A500 HD8 unit with the PC286 expansion card from the A500 power source is discouraged in all cases.  Continue to use the provided PSU for the HD8.

Use of 3rd party replacement A500 PSUs which do not employ a power cable voltage-drop compenasation circuit on their cable/in the PSU (as the original PSU has) are also discouraged.

Use of a flash-based replacement SCSI device unit (SCSI2SD, BlueSCSI, ZuluSCI) generally removes any need for 12v, and so the fan can also be omitted.  

When modifying the pads at the left-rear to run from the A500, disconnect the v5 PSU source pad, and run a heavier wire from either of pin 5/6 from the edge conenctor to the internal 5v pad.  The traces on the PCB are thin, and the direct wire will reduce the possibility of resistance voltage drop.

There is an electrolytic cap on the A500, C712, on the reset circuit. When it dries out, the A500 comes out of power-on reset too quickly.  The A500-HD8, powered from the Amiga, may not reach electrical stability before the Amiga CPU begins to execute Kickstart, and a Guru is flashed.  A Ctrl-A-A (warm reset) always solves the issue.  Replacing the cap with same, or slightly increasng the value, will generally solve the power-on Guru.