Hi,
As I have a lot of Spectrums in various states, I want to build a 48K rubber key version that I am going to use for playing games (usually I play games on a Toastrack machine).
Which board is the most reliable in terms of the DC-DC converter?
I have all types of boards from Issue1 to issue 6A but I am talking here about 3, 3B, 4A, 4B and 6A.
Also I have learned that some modifications were made to the /RAS line starting issue 4A. Would that affect the overall stability of the system?
I'll be using a modern ULA replacement that is supposed to emulate the 6C001E-7 ULA
Thanks.
Which board type?
Re: Which board type?
I don't think it matters terribly much. If you are just looking at the DC-DC converter, they are all weak and any failure of the old 4116 RAMs is going to affect machine reliability.
If you really want to avoid this, it's relatively trivial to redesign any of the board to work with an external DC-DC converter, or you could go the way of having a small supply of RAMs and components, and socket everything... But the Spectrums are not as unreliable as they were in the 80s when it was common to do stuff like removing the expansion ports without powering them down... Mainly because we were kids and we were impatient. But other than this, it was mosly 4116 RAM failures that caused the DC-DC failure, and you could even replace them with 4164s with some slight modification, and it doesn't sound like repairs are an issue for you.
But you can even socket transistors if you need, and a small supply of the relevant transistors and chips would make a repair due to a RAM and subsequently a DC-DC failure unlikely.
So with that in mind, I'd say something before 6A, because that has the integrated multiplexer chip... One more custom chip to go wrong ( though they are cheap to replace at the moment, but it won't always be like that ).
4B has excellent circuit board quality that I have seen, so is more reliable to desolder. But 3A onwards this is not really a problem.
So I'd suggest using another criteria for your selection... Do you want to keep the board stock? Or will you replace the 7805? New or original keyboard? Colour of the board preferences? Video quality? All mods made or left original?
If I just wanted a workhorse? I'd go 3B.... Still relatively common, easy to get parts for, slightly cheaper than most other models on Ebay and they are well documented and easy to desolder every chip and replace it with a socket, then clean up the chips and put them back. This would make your ongoing use far easier to maintain.
And maybe even get an Interface 1 and Microdrive while you're at it
And maybe a microdrive emulator too.
David.
If you really want to avoid this, it's relatively trivial to redesign any of the board to work with an external DC-DC converter, or you could go the way of having a small supply of RAMs and components, and socket everything... But the Spectrums are not as unreliable as they were in the 80s when it was common to do stuff like removing the expansion ports without powering them down... Mainly because we were kids and we were impatient. But other than this, it was mosly 4116 RAM failures that caused the DC-DC failure, and you could even replace them with 4164s with some slight modification, and it doesn't sound like repairs are an issue for you.
But you can even socket transistors if you need, and a small supply of the relevant transistors and chips would make a repair due to a RAM and subsequently a DC-DC failure unlikely.
So with that in mind, I'd say something before 6A, because that has the integrated multiplexer chip... One more custom chip to go wrong ( though they are cheap to replace at the moment, but it won't always be like that ).
4B has excellent circuit board quality that I have seen, so is more reliable to desolder. But 3A onwards this is not really a problem.
So I'd suggest using another criteria for your selection... Do you want to keep the board stock? Or will you replace the 7805? New or original keyboard? Colour of the board preferences? Video quality? All mods made or left original?
If I just wanted a workhorse? I'd go 3B.... Still relatively common, easy to get parts for, slightly cheaper than most other models on Ebay and they are well documented and easy to desolder every chip and replace it with a socket, then clean up the chips and put them back. This would make your ongoing use far easier to maintain.
And maybe even get an Interface 1 and Microdrive while you're at it
And maybe a microdrive emulator too.David.
Re: Which board type?
Well it's a good idea to use older 3b boards. I did not think of the Pcf1036 chips and you are right: one more custom chip to fail.
I do not have an external power supply in mind, that should provide all three voltages but the linear regulator is going to be replaced.
Also the ULA is going to be replaced by a modern chip.
I do not have an external power supply in mind, that should provide all three voltages but the linear regulator is going to be replaced.
Also the ULA is going to be replaced by a modern chip.