Hello,

i opened a A500 rev 6a and i seen something strange, some photos :
http://amigaga.chez-alice.fr/classic/amiga/a500_6a/hack_a500.jpg
http://amigaga.chez-alice.fr/classic/amiga/a500_6a/hack_a500-2.jpg
http://amigaga.chez-alice.fr/classic/amiga/a500_6a/hack_a500-3.jpg

Wire is connected in pin 26 of Gary ( /CDAC )
PCB remplace U35 ( 74F244 )

/CDAC is a clock at 7.09/7.16MHz if PAL/NTSC ( http://pinouts.ru/Motherboard/VideoExpansionAmiga_pinout.shtml )

Is anybody know what is it ?
Thanks

Last edited by Get27 on 14-Apr-2009 at 11:13 PM.

@Get27

Could be that the A500 had once a RAM-expansion installed that had more than 512kB "Ranger"-Mem, as these needed some extra wires to Gary. No idea how that extra PCB would fit into this ...

_________________
- We don't need good ideas, we haven't run out on bad ones yet
- blame Canada

@Get27

Interesting. The PCB looks professional, but the soldering is ####e. This means either it's a DIY job with professional parts, a technician or a factory job with less-than-satisfactory training

It is NOT a part of an expansion board, those would plug in to the memory port and carry wires to Gary's socket. Seriously, I cannot think of any reason why they would do this. U34 and U35 (the two F244s in the 6A I have here) separate the chip memory from the fast memory so that the chipset can run DMA on the chip memory behind the scenes.

Replacing one of them with something else doesn't sound right. Replacing one of them with something that does the same but in a different way is plausible, but very weird. Replacing one of them with something that does the same and more doesn't sound quite right either

I wish we could see under that board

_________________
This weeks pet peeve:
Using "voltage" instead of "potential", which leads to inventing new words like "amperage" instead of "current" (I, measured in A) or possible "charge" (amperehours, Ah or Coulomb, C). Sometimes I don't even know what people mean.

@Get27

The 74F244 is a three-state buffer which is normally used to make part of a circuit temporarily "disappear", so the board is clearly meant to sit in the middle of a signal path and snoop it and/or interfere with the signals. Kinda like a modchip one would put in a console to play "backup" games but I don't quite see the point of modchipping an A500. Did you buy the A500 new, or get it used off eBay?

Thanks for your answers.


@CodeSmith

I bought it on ebay and the prdecessor doesn't know what is it (and he bought it on ebay before...)

There's anothers differences between "normal" rev6a :
- there's no resistor added on the CIA (A).
- capacitors added on RP405 is not the same
- R401 R405 R406 R408 E501 E502 E503 are only 1/2W instead of 1W
The board seems to works normally (boot, games...)


@Olegil

I will remove pins and make a photo of the other side.

Last edited by Get27 on 03-Aug-2008 at 11:01 PM.

@Get27

check which version of Agnus you have I suspect a Chipmem hack.
later on Commodore ran out of the the old Agnus and started sticking in the 2 MEG fat agnus.

Stick in a memory expansion and see if it registers as chipmem or as fast mem.

Ohh my memory just kicked over. Boot the machine without a memory expansion and see how much it reports it just might report 1 or 2 MEG CHIPMEM onboard without memory expansion. I also remember the 2 meg A500's had a jumper underneath the motherboard connecting the last pin on all the memory together.

A regular A500 should report just 512 Meg Chipmem


Kgrach

@kgrach

Hello, only 512ko chip memory.
On the board, welcome to Agnus 8371

With a A501 - 512kb expansion ram, sysinfo say slow memory ( $00C00000 )

The sticker is dated 1987-1988. Serial 686593.
Apparently it was one of the firsts rev6a made

http://amigaga.chez-alice.fr/classic/amiga/a500_6a/hack_a500-4.jpg
http://amigaga.chez-alice.fr/classic/amiga/a500_6a/hack_a500-5.jpg

Last edited by Get27 on 14-Apr-2009 at 11:14 PM.
Last edited by Get27 on 03-Aug-2008 at 11:27 PM.
Last edited by Get27 on 03-Aug-2008 at 11:11 PM.

@olegil

Let's have a look
http://amigaga.chez-alice.fr/classic/amiga/a500_6a/hack_a500-6.jpg
http://amigaga.chez-alice.fr/classic/amiga/a500_6a/hack_a500-7.jpg
http://amigaga.chez-alice.fr/classic/amiga/a500_6a/hack_a500-8.jpg

so it seems to be a commodore hack

Last edited by Get27 on 14-Apr-2009 at 11:14 PM.
Last edited by Get27 on 04-Aug-2008 at 12:08 AM.

@Get27

The chip with the sticker on it is a PAL (programmable logic), probably a 16V8 since it's got 20 pins; see eg here. So whatever it does, it's not terribly complicated. Someone with the right equipment and a weekend to burn could probably even reverse engineer it and tell you exactly what it does.

Last edited by CodeSmith on 04-Aug-2008 at 12:54 AM.

Hi guys,

I'm very curious as to what this is. I noticed I have the same thing on my A500 revision 6a motherboard. Anyone knows? Thanks in advance!

_________________
Old School Game Blog
Gaming on AmigaOS 4
Void - Amiga Demo Group

@Get27

probably the batch of this a500 was made by commodore factory before a new revision exit and they fix the already made mobos with this hack.

_________________
I love Amiga and new hope by AmigaNG
A 500 + ; CDTV; CD32;
PowerMac G5 Quad 8GB,SSD,SSHD,7800gtx,Radeon R5 230 2GB;
MacBook Pro Retina I7 2.3ghz;
#nomorea-eoninmyhome