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AuthorTopic: What A500 do I have?  (Read 1060 times)

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Offline Protek

What A500 do I have?
« on: October 08, 2008, 07:00:04 AM »
I've been wondering my A500 ever since I installed an 2.05 ROM into it. With the trapdoor mem expansion in place, the WB says that it has 1 MB of Chip and 0 other. I thought this was a glitch in WB but the hw info in tools says that the A500 has ECS PAL Agnus and normal Denise. The Agnus chip is 8372A and on the mobo it has 512K/1M printed and there are empty places for memory chips on it. Is this a late revision A500 just prior to A500+?
A4000/040 3.1/3.1, 2 MB Chip, 24 MB Fast, Piccolo SD64 2MB, GVP A2000mHC+8 Rev2, 4 GB CF HD via CF IDE
A1200 3.1/3.9, Blizzard 1230MkIV 030@50 with SCSI kit, 2 MB Chip, 128 MB Fast, 1 GB CF HD via CF IDE
A600 3.1/3.1, 2 MB Chip, A603, 1GB CF HD via CF IDE
 

Offline Damion

Re: What A500 do I have?
« Reply #1 on: October 08, 2008, 07:26:27 AM »
You probably have a 6A motherboard, last revision before the A500+.

edit -- I've heard mention of some very late A500's actually having A500+ rev 8A motherboards (possibly C= refurbs?), though that would definitely not be common.

 

Offline Chain

Re: What A500 do I have?
« Reply #2 on: October 08, 2008, 07:29:23 AM »
1mb chip with trapdoor? it sure must be rejumpered coz standard cfg is 512k chip+512k slow
too lazy to use shift key properly...
 

Offline Protek

Re: What A500 do I have?
« Reply #3 on: October 08, 2008, 07:50:22 AM »
Quote


edit -- I've heard mention of some very late A500's actually having A500+ rev 8A motherboards (possibly C= refurbs?), though that would definitely not be common.


According to BBOAH, the A500 that are badged "A500" instead of "C=", should be rev 8A. There was one for auction at the local auction site.
A4000/040 3.1/3.1, 2 MB Chip, 24 MB Fast, Piccolo SD64 2MB, GVP A2000mHC+8 Rev2, 4 GB CF HD via CF IDE
A1200 3.1/3.9, Blizzard 1230MkIV 030@50 with SCSI kit, 2 MB Chip, 128 MB Fast, 1 GB CF HD via CF IDE
A600 3.1/3.1, 2 MB Chip, A603, 1GB CF HD via CF IDE
 

Offline darksun9210

Re: What A500 do I have?
« Reply #4 on: October 08, 2008, 08:20:26 AM »
Agreed with -D- on the the Rev6 thoughts. especially as you have the 512k/1Mb markings and empty holes for memory. if you get the right chips and caps, you can solder them onto the board in the empty spaces. but it would be fairly pointless as these would occupy the same address space as the trapdoor slot.

sounds like you have a 1meg agnus as these report back as ECS chips and the jumper/cut fix to mark the trapdoor memory as chip ram.

have you have the machine from new, or is it 2nd hand? if it is 2nd hand, i'd suspect the jumper/fix trick.

i thought rev8 A500's were plusses and had a full 1Meg on board, (all the sockets full) and the trapdoor mapped to the upper meg of the chipram range?

i would have done this myself to mine, but i only have a half meg agnus...

A500 Vampire2/minimegachip/lazarus/indyECS, (+GVP A530,SupraTurbo28,GVP HD8)
A600 Vampire2/604n/subway/IndyECS, (+ACA630)
A1200 Vampire2/IndyAGA, (+Bliz030+scsi)
A1200 Bliz040+scsi/subway/indyAGA
A1200 BlizPPCscsi/Bvision/subway
A3k CSmk3-060/CV64-3D/Xsurf100+RRoadUSB/Zoram256/acard scsi-ide-CF/IndyECS,
A4k C=040/CV64-3D/Xsurf100+RRoadUSB/Bigram256/IndyAGA, (also mediator+pci cards)
CD32 TF330/IndyAGA
Plus an SGI O2 & consoles.
 

Offline Protek

Re: What A500 do I have?
« Reply #5 on: October 08, 2008, 09:24:03 AM »
Quote

darksun9210 wrote:

sounds like you have a 1meg agnus as these report back as ECS chips and the jumper/cut fix to mark the trapdoor memory as chip ram.

have you have the machine from new, or is it 2nd hand? if it is 2nd hand, i'd suspect the jumper/fix trick.


It's a second hand machine, picked from a local recycling center. Where the jumper or trace cut can be located?

So, it's either 1 Meg chip or 512/512 chip/slow, right? No possibility for 1 Meg chip/512 slow?

This is an interesting machine. At first I wasn't able to get a picture to it even though it was clearly booting. Swapping the CIA's or more likely re-seating the CIA's seemed to help. Still need to find a working keyboard, since the right "Amiga" button isn't working. Can't arrange icons or make soft reset. Might have to look for an fast mem expansion for it. I have IDE68K HD adapter with a 1 GB CF card installed, so doesn't really make sense to get a SCSI controller with memory. I was positively surprised that the whole 1GB was available with revision 37.300 of the 2.05 ROM.

Edit: Would the rev 6A mobo be a good basis for fully ECS compliant A500, basically A500+? If you change the 8372A to 8375 Super Agnus, Denise to Super Denise and add the missing memory chips, would you then basically have an A500+, with possibility to use 1MB expansions?
A4000/040 3.1/3.1, 2 MB Chip, 24 MB Fast, Piccolo SD64 2MB, GVP A2000mHC+8 Rev2, 4 GB CF HD via CF IDE
A1200 3.1/3.9, Blizzard 1230MkIV 030@50 with SCSI kit, 2 MB Chip, 128 MB Fast, 1 GB CF HD via CF IDE
A600 3.1/3.1, 2 MB Chip, A603, 1GB CF HD via CF IDE
 

Offline darksun9210

Re: What A500 do I have?
« Reply #6 on: October 08, 2008, 11:17:54 AM »
ok, then from what i can guess, you have a rev6/6a mainboard with a 1Meg agnus onboard. it seems to have had the jumper/cut mod done on it to get 1Meg chipram.  converting what would have been a 512/512 chip/slow to a 512/512 chip/chip config. the first 512 being the motherboard ram, the 2nd 512 being the trapdoor / empty motherboard spaces.
to get more ram in the trapdoor, you'll need either, (and i have seen these) a trapdoor ram expansion that has a pass through that you bolt your existing trapdoor expansion onto, or something like an ICD adram 540, or solder chips to the mainboard and route some signal lines from gary to the trapdoor. either way, you'll need something that grabs some addressing signals from the gary chip.
best thing to do is get a sidecar expansion if you want more ram. plus it'll be faster as the cpu isn't having to go over the custom chip bus to get to the memory, which is what it has to do for "slow" fast ram, and why "slow" fast ram is convertable to chipram, as it is on the chipram bus.

you'll never get more than 1Meg of chip ram in there without upgrading to a 2Meg agnus which doesn't fit the socket you have., hence the minimegachip upgrade boards

thinking about it as i type this, i think for the 1Mb chip / 512k (slow)fast you are asking about, still needs a 2Meg agnus as it is the agnus chip that controls access to memory in that address range. and i guess this would not be possible without a minimegachip 2Meg agnus upgrade board. but then, how did the Adram boards work putting 1.8Mb into the trapdoor slot? :crazy:

forget adding more ram to the trapdoor, get a 2-8Mb side expansion off of ebay for 30 quid or something :-)

A500 Vampire2/minimegachip/lazarus/indyECS, (+GVP A530,SupraTurbo28,GVP HD8)
A600 Vampire2/604n/subway/IndyECS, (+ACA630)
A1200 Vampire2/IndyAGA, (+Bliz030+scsi)
A1200 Bliz040+scsi/subway/indyAGA
A1200 BlizPPCscsi/Bvision/subway
A3k CSmk3-060/CV64-3D/Xsurf100+RRoadUSB/Zoram256/acard scsi-ide-CF/IndyECS,
A4k C=040/CV64-3D/Xsurf100+RRoadUSB/Bigram256/IndyAGA, (also mediator+pci cards)
CD32 TF330/IndyAGA
Plus an SGI O2 & consoles.
 

Offline darksun9210

Re: What A500 do I have?
« Reply #7 on: October 08, 2008, 11:26:05 AM »
just found the expansion systems baseboard puts 4Mb into the A500's trapdoor! :-o  but forget these as i guess they are going to be VERY hard to find!  :lol:

A500 Vampire2/minimegachip/lazarus/indyECS, (+GVP A530,SupraTurbo28,GVP HD8)
A600 Vampire2/604n/subway/IndyECS, (+ACA630)
A1200 Vampire2/IndyAGA, (+Bliz030+scsi)
A1200 Bliz040+scsi/subway/indyAGA
A1200 BlizPPCscsi/Bvision/subway
A3k CSmk3-060/CV64-3D/Xsurf100+RRoadUSB/Zoram256/acard scsi-ide-CF/IndyECS,
A4k C=040/CV64-3D/Xsurf100+RRoadUSB/Bigram256/IndyAGA, (also mediator+pci cards)
CD32 TF330/IndyAGA
Plus an SGI O2 & consoles.
 

Offline Protek

Re: What A500 do I have?
« Reply #8 on: October 08, 2008, 11:37:52 AM »
Thanks for the info! Have to endure the side expansion ram option at some point. Memory expansion for A2000 has higher priority ATM. :)
A4000/040 3.1/3.1, 2 MB Chip, 24 MB Fast, Piccolo SD64 2MB, GVP A2000mHC+8 Rev2, 4 GB CF HD via CF IDE
A1200 3.1/3.9, Blizzard 1230MkIV 030@50 with SCSI kit, 2 MB Chip, 128 MB Fast, 1 GB CF HD via CF IDE
A600 3.1/3.1, 2 MB Chip, A603, 1GB CF HD via CF IDE
 

Offline Metalguy66

Re: What A500 do I have?
« Reply #9 on: October 09, 2008, 10:08:41 PM »
Use of Additional Ram on the A500:

First thing you need to do is pop the case back apart and look at the board on the extreme right side, just in front of the disk drive, and find out for sure what revision motherboard you do in fact have.

If you have rev 6a A500 motherboard:
Those "empty spaces" where the RAM chips are are for the option of installing a full 1 meg of chipram on the motherboard. If you do populate these "empty spaces" with 44256 (or equivelant 256k x 4 DRAM chips) and make the appropriate jumper changes, your machine will have 1 meg of chipram on the motherboard, and will no longer look for the upper 512k of chipram on the trapdoor expansion. With this configuration, any RAM you do plug into the trap-door expansion slot will show up as "fast ram" but will in fact be what some people refer to as "slow ram".. That is, it is not directly adressable by the custom chips, and access by the CPU to this ram will suffer from bus cotention with the agnus chip, since it is on the chipram bus. So really, if you already have 512k of ram in the trap door expansion slot, and it is showing up as chip ram, its best to leave it alone and look for a ram expansion that goes on the side-car expansion or an accelerator board for additional fast ram solutions.

If you have a Rev 8a (A500+) Motherboard:
Some later model A500s were actually built with the A500+ motherboard. Commodore did this to reduce production costs in later years by only producing one board for both machines. This is good news because you can easily upgrade this to a full blown A500+ and even add up to 2 megs of chip ram. The first step involves installing the 8375 AGNUS chip, moving several motherboard jumpers, adding U32 (74F139 demux IC which was left off of 8a boards built in "a500 configuration"), and adding four more 44256 (or equivelant 256k x 4 DRAM chips) to the "empty spaces" in between the existing DRAM chips. This will get you to a state where there is 1 meg of chip ram on the motherboard.  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 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...

Have fun....


------------------------------------------------------------------
kjones66@earthlink.net  http://www.rasterline.com
AMIGA & ATARI 8-BIT repairs, upgrades, mods, restoration.
 

Offline rkauer

Re: What A500 do I have?
« Reply #10 on: October 09, 2008, 11:35:14 PM »
 Excellent answer Metalguy66!:bowdown:

 But one minor correction: C= use to use NiCd barrel batteries inside A501 (and in A500+ motherboard too, along other Amiga models).

 NiMH batteries are available today to replace those ancient, leak-prone units. Personally, I like 2032 replacement approach.:-)

 BTW: welcome back to Amiga land!
Goodbye people.

I\'ll pop on from time to time, RL is acting up.
 

Offline darksun9210

Re: What A500 do I have?
« Reply #11 on: October 10, 2008, 08:00:20 AM »
good skills Metalguy66! especially on the piggyback ram thing! :-)
would this work on a rev5 A500 if i was able to get a 2Meg agnus fitted? :-? or am i as i suspect, stuffed? :lol:

A500 Vampire2/minimegachip/lazarus/indyECS, (+GVP A530,SupraTurbo28,GVP HD8)
A600 Vampire2/604n/subway/IndyECS, (+ACA630)
A1200 Vampire2/IndyAGA, (+Bliz030+scsi)
A1200 Bliz040+scsi/subway/indyAGA
A1200 BlizPPCscsi/Bvision/subway
A3k CSmk3-060/CV64-3D/Xsurf100+RRoadUSB/Zoram256/acard scsi-ide-CF/IndyECS,
A4k C=040/CV64-3D/Xsurf100+RRoadUSB/Bigram256/IndyAGA, (also mediator+pci cards)
CD32 TF330/IndyAGA
Plus an SGI O2 & consoles.
 

Offline Metalguy66

Re: What A500 do I have?
« Reply #12 on: October 10, 2008, 03:58:07 PM »
I would not reccomend trying a "Do it yourself" 2 meg chipram upgrade for a rev 5.

It is possible, but it requires the addition of quite a few circuits to Agnus & Gary, in addtion to the 8375, the extra 74LS139, and the extra ram..

Also, The Rev 5. uses sixteen 256 x 1 DRAMS to make 512k, (instead of four 256k x 4 DRAMS as is used on the rev 6a).. So if you were "piggybacking" it all on the motherboard, you'd need forty-eight more 256k x 1 DRAM chips to get you to 2 meg! This would not fit under the keyboard, would be a soldering nightmare, would increase the power consumption of the motherboard substantially, might cause heat dissipation issues with some of the DRAMs, and would certainly require additional decoupling caps...

So basically, a project like that would involve building a separate PCB in order to do it in any decent/reliable form.  

Here's what I reccomend for a Rev. 5 Motherboard:
If you want 1 meg of chip, just make sure you have the 8372A agnus, and a 512k expansion in your tapdoor.  If you want 2 megs chip ram, you need to find one of the upgrade boards that plugs in the agnus socket (eg. DKB Megachip, Minimeg, etc.)

But really, the best upgrade for your A500 is an A500+ (rev 8a) motherboard. They sell them on EBAY fairly often/cheap, usually from sellers in the UK/Europe.
 
------------------------------------------------------------------
kjones66@earthlink.net  http://www.rasterline.com
AMIGA & ATARI 8-BIT repairs, upgrades, mods, restoration.