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

Change / remove jumper blobs

JP2 setting

JP7A & JP9 setting

Finished board

The complete machine

See: key cleaning I did for the machine..