English Amiga Board - View Single Post - 0.5mb trapdoor expansion on 1mb A500+..still only 1mb ??

25 January 2019, 19:57

I have a A500+ with 1mb chipram internal.It should have been a A500 that is modified to A500+,so it´s not a native factory build A500+.
It´s a Rev 8a board and it´s Kickstart 2.0

I have a 0.5mb trapdoor expansion that I have tried to use also (it's working 100% on a regular stock 0.5mb A500 with Kickstart1.3) but the Amiga still only shows 1mb.
I´ve posted about this issue on Facebook and a user suggested to solder a 74F139 IC onto location U32 and also remove solder from the jumper pads on U32. I´ve done this(and also added a socket for the 74F139) and still there is only 1mb shown. I have tried booting without the 74F139 but it just shows a green screen. With 74F139 added it boots normally but only shows 1mb,so the 74F139 is diong something to the system.

So have anyone any ideas etc. why the A500+ don¨t show a total of 1.5mb ??
I have checked the traces using Amiga PCB Explorer site and as I can see/understand ,there is no broken traces (I´m not a electronics expert).
I´ve tested continuity with a multmeter that BEEPS when probes are connected.

Is there still some things/mods missing to the Amiga?
Could there be mods to the trapdoor in order to work with a A500+ ??

25 January 2019, 19:57	#1
cinnober Posts: n/a	0.5mb trapdoor expansion on 1mb A500+..still only 1mb ?? I have a A500+ with 1mb chipram internal.It should have been a A500 that is modified to A500+,so it´s not a native factory build A500+. It´s a Rev 8a board and it´s Kickstart 2.0 I have a 0.5mb trapdoor expansion that I have tried to use also (it's working 100% on a regular stock 0.5mb A500 with Kickstart1.3) but the Amiga still only shows 1mb. I´ve posted about this issue on Facebook and a user suggested to solder a 74F139 IC onto location U32 and also remove solder from the jumper pads on U32. I´ve done this(and also added a socket for the 74F139) and still there is only 1mb shown. I have tried booting without the 74F139 but it just shows a green screen. With 74F139 added it boots normally but only shows 1mb,so the 74F139 is diong something to the system. So have anyone any ideas etc. why the A500+ don¨t show a total of 1.5mb ?? I have checked the traces using Amiga PCB Explorer site and as I can see/understand ,there is no broken traces (I´m not a electronics expert). I´ve tested continuity with a multmeter that BEEPS when probes are connected. Is there still some things/mods missing to the Amiga? Could there be mods to the trapdoor in order to work with a A500+ ??