[#19]
Re: A500 rev.8a + wlutowanie pamięci na płytę, czyli konfiguracja pamięci w A500
@posylus,
post #17
Sprawa jasna, znalazłem dokładny opis gościa który to zrobił i opisał krok po kroku:
* i also have some of these stripped down 8a boards here and have successfully upgraded one of them back from 512k chipmem to full 2Meg!
steps to do:
populate the 4 empty ram sockets with compatible ram chips
change JP2 as described above to enable them as second 512k chipmem and not as C0 fastmem.
change both JP3 from II back to = setting. this will map the expansion (trapdoor) mem to onboard mem.
open jp7a, this will disable the trapdoor fastmem feature
remove the trapdoor memory card!
do not touch the solder blobs at U32!
you should now have 1 Meg chipram with onboard memory.
i you want 1.5 or even 2 meg chipram, do the following steps additional:
open the solder blobs at U32, so they look like the pic from zetr0.
populate the 74F139, it MUST be a F type, not an LS type!
put a 512k memboard in the trapdoor
disable the trapdoor with the jumper on the card (maybe it even works without doing so)
You should now have 1.5 Meg Chipram!
For 2 Meg, just swap out the 512k trapdoor memboard against a 1 Meg board from an a500+
This works 100% on mine system here!
Dodam tylko, że te "solder blobs at U32" które trzeba usunąć po dodaniu demuxa, to właśnie jp4 (A i B).
Sam U32 dekoduje adresy powyżej 1 MB chip RAM, bez niego sygnały CAS dla górnego 1 MB nie trafiają gdzie trzeba.
Co ciekawe, gość pisze, że po zrobieniu przeróbki można wykorzystywać rozszerzenie od A500, otrzymując 1.5 MB chip. Oczywiście wtedy nie lutujemy dodatkowego RAMu na "plecach" starego.
Tutaj opis drugiej części przeróbki (autorstwa innego gościa): lutowanie drugiego 1 MB na płycie i RTC na płycie:
** To get the second meg of chip ram, you can either find an A501+ (or third party manufactured equivelant) which is an additional 1 meg chip ram expansion that goes in the trap door expansion slot, or you can "piggyback" another eight 44256 DRAM chips on top of the existing ones, bend up pin 17 on each chip, and connect all the "pin 17s" of the left 4 chips to pin 11 of U32, and all the "pin 17s" of the right 4 chips to pin 5 of U32. [[This looks/sounds easy, but be advised that the DRAM chips are mounted rather close together when you have all 8 populated, and soldering another 8 on top of them can take some serious skill with a soldering iron. It shouldnt be a problem for experienced techs, but the average hobbyist should think twice.. If you put too much heat on the DRAMs, you can fry them, and if you create any solder bridges between pins, you've got a serious mess to straighten out.. also if you fail to make a good solder connection on any pins, you can cause operational flakiness/reliability issues.]] Once this is done, you will have 2 megs of chip ram. The other thing you can do is populate the circuitry to add the RTC (realtime clock/calendar) to the motherboard. I wont go into this in detail, but the components are exactly the same as the ones used on the RTC section of a standard A501. Here (http://www.devili.iki.fi/mirrors/4x4.hopto.org/A500PlusR1.zip) is the A500+ service manual which has full schematics, component values, and board layout diagrams. The last thing I'll say about this is that the battery used by commodore here was an old NiMH or Zinc "barrel" type battery.. These are famous for leaking and destroying AMIGA motherboards. I use a standard CR2032 replaceable "coin" type Lithium battery socket from an old PC motherboard here. It has worked fine for me even though the CR2032 is only 3.0v and the orginal batteries were 3.6v...
Ostatnia aktualizacja: 24.02.2012 11:25:14 przez wali7
Ostatnia aktualizacja: 24.02.2012 11:26:44 przez wali7