Dick Smith System 80 - 4164 RAM Conversion completed
Posted: Sat Jul 25, 2015 4:01 pmHi all,
Thought it would be worthwhile sharing that I have completed a 4164 RAM conversion on my System 80.
I read Terry's site (and blog) on the subject and I was a little hesitant at first, especially when I read a board got destroyed. Being an elec engineer I decided to study the instructions from 'John Gilbert and Co' with reference to a crude sketch of a circuit anyway. A few hours of cross checking datasheets and the actual motherboard and I was almost ready to go. The main problem was the guide does not go into detail as to why traces are cut and joined; but with patience and consulting the 4116 and 4164 datasheets it makes 100% sense. I also noticed while the guide is 100% technically correct, some instructions would not be easily interpreted by someone without an electronics background. This is especially applicable when it talks about cutting the trace from the 5.1V zener diode. The trace it talks about passes through a via from top to bottom layer. As such if you casually glance at it you will cut the wrong trace.
The main reason I decided to go down this route is I wanted to avoid piggybacking IC's. Having played with vintage gear for some time now I find that RAM is one of the most unreliable element in any system. Having to desolder a stack of IC's to troubleshoot issues in the future doesn't appeal to me; so I decided to go the slightly harder but simpler route. Also despite the fact it says 'cut this trace' it really isn't destructive. All the cut traces can be resoldered with ease if required.
I took a heap of photo's and made some notes. If people are interested I'll type something up soon regarding the conversion which will hopefully help out people in the future.
**Note that this upgrade will not work with all 4164 IC's. You need to find a 4164 that is of '128 cycle' type; or lists as refresh compatible with 16K DRAM. If you obtain 256 cycle type it will not work as the Z80 in these machines only has a 7-bit refresh. My chip of choice was the Hitachi HM4864P-2. In the datasheet it explicitly states that it is refresh compatible with 4116 DRAM.
Thought it would be worthwhile sharing that I have completed a 4164 RAM conversion on my System 80.
I read Terry's site (and blog) on the subject and I was a little hesitant at first, especially when I read a board got destroyed. Being an elec engineer I decided to study the instructions from 'John Gilbert and Co' with reference to a crude sketch of a circuit anyway. A few hours of cross checking datasheets and the actual motherboard and I was almost ready to go. The main problem was the guide does not go into detail as to why traces are cut and joined; but with patience and consulting the 4116 and 4164 datasheets it makes 100% sense. I also noticed while the guide is 100% technically correct, some instructions would not be easily interpreted by someone without an electronics background. This is especially applicable when it talks about cutting the trace from the 5.1V zener diode. The trace it talks about passes through a via from top to bottom layer. As such if you casually glance at it you will cut the wrong trace.
The main reason I decided to go down this route is I wanted to avoid piggybacking IC's. Having played with vintage gear for some time now I find that RAM is one of the most unreliable element in any system. Having to desolder a stack of IC's to troubleshoot issues in the future doesn't appeal to me; so I decided to go the slightly harder but simpler route. Also despite the fact it says 'cut this trace' it really isn't destructive. All the cut traces can be resoldered with ease if required.
I took a heap of photo's and made some notes. If people are interested I'll type something up soon regarding the conversion which will hopefully help out people in the future.
**Note that this upgrade will not work with all 4164 IC's. You need to find a 4164 that is of '128 cycle' type; or lists as refresh compatible with 16K DRAM. If you obtain 256 cycle type it will not work as the Z80 in these machines only has a 7-bit refresh. My chip of choice was the Hitachi HM4864P-2. In the datasheet it explicitly states that it is refresh compatible with 4116 DRAM.
