There is a difference in current, I think +12V line due to FDD.
Using +3 supply with +2A/B is safe, +2A supply may be overloaded with +3, especially with external interfaces.
However, +2A is enough to boot +3 with divIDE, I did it many times.
The +2 PSU will fail when the +3 uses the +12v for the FDD - this will take the +12v rail out as its not rated for the use with the 3" drive.
While the +2 PSU may work (albeit temporarily) with the +3, it will fail when you start accessing the DISK - and the DISK is always active seek on boot. I would suggest against it personally. Sadly I have about 6 +2PSU's that have all suffered from this type of death.
From what I remember, a 1 A regulator is used to generate 12 V in both versions of the supply and it'd probably take longer term abuse to make that fail.
In the +2A/B supply, -12 V is produced by a small regulator (I think rated for 100 mA) and that'd probably fail much more readily.
Whatever goes wrong with the regulation circuit, it's probably not very difficult to repair in most cases; they are fairly simple.
+2A PSU uses:-
+12V ... IC2 (7812) and C2 (1000uF)
-12V ... IC3 (79L12) and C3 (330uF)
both the above supplies come from a common secondary transformer winding via a shared bridge rectifier formed from four 1N4001 diodes (rated 1A max) .
+3 PSU uses:-
+12V ... IC2 (7812), C4 (3300uF), F2 (1.25A) via a bridge rectifier formed from four 1N5391 diodes (rated 1.5A max) and its own secondary transformer winding.
-12V ... D7 (12V Zener diode), R1 (10 Ohms), C8 (3300uf) and a bridge rectifier formed from four 1N4001 diodes and its own secondary transformer winding.
So as you can see, the +12V supply on the +3 PSU is constructed to supply higher currents than the +12V supply in the +2A PSU, even though they both use the same 7812 voltage regulator chip.
We don't know the full specifications of the transformer windings, but the +2A secondary winding is likely to be made of smaller diameter wire (compared to that on the +3 PSU), which when heavily loaded will reduce the output voltage somewhat.
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without a fair bit of work I am afraid - it would be easier to repurpose an ATX power supply that to try and re-work the +2A/B PSU to get more Amperage.
I did promise guesser that I would draw up a schematic of the +2A/B PSU - when I get some time I shall do this =)
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
Comments
Using +3 supply with +2A/B is safe, +2A supply may be overloaded with +3, especially with external interfaces.
However, +2A is enough to boot +3 with divIDE, I did it many times.
This might help -
The +2 PSU will fail when the +3 uses the +12v for the FDD - this will take the +12v rail out as its not rated for the use with the 3" drive.
While the +2 PSU may work (albeit temporarily) with the +3, it will fail when you start accessing the DISK - and the DISK is always active seek on boot. I would suggest against it personally. Sadly I have about 6 +2PSU's that have all suffered from this type of death.
In the +2A/B supply, -12 V is produced by a small regulator (I think rated for 100 mA) and that'd probably fail much more readily.
Whatever goes wrong with the regulation circuit, it's probably not very difficult to repair in most cases; they are fairly simple.
+12V ... IC2 (7812) and C2 (1000uF)
-12V ... IC3 (79L12) and C3 (330uF)
both the above supplies come from a common secondary transformer winding via a shared bridge rectifier formed from four 1N4001 diodes (rated 1A max) .
+3 PSU uses:-
+12V ... IC2 (7812), C4 (3300uF), F2 (1.25A) via a bridge rectifier formed from four 1N5391 diodes (rated 1.5A max) and its own secondary transformer winding.
-12V ... D7 (12V Zener diode), R1 (10 Ohms), C8 (3300uf) and a bridge rectifier formed from four 1N4001 diodes and its own secondary transformer winding.
So as you can see, the +12V supply on the +3 PSU is constructed to supply higher currents than the +12V supply in the +2A PSU, even though they both use the same 7812 voltage regulator chip.
We don't know the full specifications of the transformer windings, but the +2A secondary winding is likely to be made of smaller diameter wire (compared to that on the +3 PSU), which when heavily loaded will reduce the output voltage somewhat.
Mark
Repair Guides. Spanish Hardware site.
WoS - can't download? Info here...
former Meulie Spectrum Archive but no longer available :-(
Spectranet: the TNFS directory thread
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
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I guess that Amstrad didn't made two different designs for +2A/+3 PSUs, so a +2A PSU may be a de-rated +3 PSU. How can a +2A PSU be upgraded to +3?
An' you know what they said?
Well, some of it was true!
without a fair bit of work I am afraid - it would be easier to repurpose an ATX power supply that to try and re-work the +2A/B PSU to get more Amperage.
I did promise guesser that I would draw up a schematic of the +2A/B PSU - when I get some time I shall do this =)
Mark
Repair Guides. Spanish Hardware site.
WoS - can't download? Info here...
former Meulie Spectrum Archive but no longer available :-(
Spectranet: the TNFS directory thread
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)