1 November 2020

Upgrade Amiga 500 rev. 8a board to Amiga 500+

A while ago I got an empty Amiga 500 plus (+) case, without keyboard and mainboard. I had a spare Amiga 500 rev.8a board (and keyboard), so I decided tot upgrade that one to an Amiga 500+. In this post I show which components must be replace on the board and which changes must be done to the board.

The board before the upgrade

Components to do the upgrade

Position Component
U19 DRAM 256K x 4bit 120ns
U18 DRAM 256K x 4bit 120ns
U17 DRAM 256K x 4bit 120ns
U16 DRAM 256K x 4bit 120ns
U32 74F139
U9 Oki MSM6242B (RealTimeClock)
Y9 Crystal 32.768Hz
TC9 Trim capacitor 6.8 – 45pF
C9 Axial 0.33uF (330nF) capacitor
C911 22pF capacitor
C913 Tantalum radial 4,7uF / 16V capacitor (I used electrolytic capacitor)
R911 470 Ohm resistor
R913 470 Ohm resistor
R914 10K Ohm resistor
D911 1N914 / 1N4148 diode
D912 1N914 / 1N4148 diode
BT9 CR2032 battery (with adaptor) if needed

Memory

Components needed: U19, U18, U17, U16, U32

First remove the solder from the holes, and place sockets (low profile) or memory to the board.

CAS signals (U32)

Remove the solder from the holes, and remove the blobs from the two jumper pads.

Clock circuit

Place components: R914, C911, C9, Y9, TC9, U9

Place components: R911, R913, D911, D912, C913

Note from Sylversio (see comments):

You just placed the components up, without considering that this PCB Schema is wrong, Where R913 should be replaced by a Diode, and D912 cathode should be connected to cathode of the new diode placed in R913 (that both connected electrically with + C913.

Otherwise you could damage your board.
Also, mention to … oscillator… should not be solder the chassis to the board.
All that become from a mistake in A500 rev8 board, that didn’t routed properly the tracks from Schema.

 

Change / remove jumper blobs

JP2 setting

Original setting

New setting

JP7A & JP9 setting

Original setting

New setting

Finished board

The complete machine

See: key cleaning I did for the machine..