Upgrade 520ST to 1 MB
A particular model of the 520 STFM can be easily upgraded to 1 MB of ram by just plugging in extra memory chips.
The motherboard
Check that the original memory chips of your 520 STFM is located underneath the Power Supply Unit, and it contains only 4 memory chips. If the meomory chips of your 520 STFM is located elsewhere then you cannot use the method described here to upgrade your 520 STFM.
On this motherboard, only one row of the memory are populated. The other row, normally will be clearly marked out and on the right side, is left blank. The 4 original memory chips makes up the existing 512KB of RAM, and so you just need to populate the 4 missing momory chips, to give you the required 1024K or 1 MB.
You will also need to have 4 capacitor, each across the power pins of the memory chips. The location of these capacitors are also clearly marked out on the motherboard.
The area underneath the power supply unit exposing the memory banks of the STFM. Notice the dust around the area, as this upgrade was done over 20 years ago!!
The red wire attaching the cut off resistor is to enable the memory banks. The memory banks was disable due to my 4 MB memory upgrade kit. As the 4 MB memory upgrade kit was removed, the red wire was soldered back to the resistor to enable again the memory banks.
You do not need to cut any resistors for the 1MB upgrade.
The original memory chips are on the left hand side, marked as TC514256P-10, a 4 x 256 bits 100ns 20 pin memory DIP. They are 1 Megabit memory chips and you have 4 of them, 4 x 1MB gives you 4096 bits which is 512KB. You need another 4 of these 1 Mbit chips to make up to 1 MB.
The added memory chips are on the right hand side, seated on sockets. They are unmarked chips from a cheap source.
Note the brown capacitor across the new memory chips.
See you at
WongCK
created: 31 Dec 2010