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per
February 29th, 2008, 09:43 AM
I recently got an Amiga 500, and it seems that the RAM expansion in the trapdoor expansion slot doesn't work.

The board consist of the 56 pin contact to connect it to the Amiga slot. one "in-to-out1/in-to-out2" switch, one 2.2uf @ 50v electrolyte cappacitor, one 100-Ohm resistor @ 1/4 W, five "104" (in the unit of "pf" I beleve) cappacitors, three "B 101G" resistor blocks and the following 16 Texas instrument IC's:
one "TMS 4256-12NL, EGP 8710"
one "TMS 4256-12NL, HGI 8607"
five "TMS 4256-12NL, HGI 8619"
two "TMS 4256-12NL, HGI 8621"
one "TMS 4256-12NL, QM41256-12P5, EHP 8826 2467"
one "TMS 4256-12NL, QM41256-12P5, EHP 8826 2847"
one "TMS 4256-12NL, QM41256-12P5, EHP 8831 2871"
one "TMS 4256-15NL, EGP 8710"
one "TMS 4256-15NL, GP 8631"
one "TMS 4256-15NL, GP 8640"
one "TMS 4256-15NL, IGE 8826".

There is no company name on the board, and the only printed text on the board is "COMPONENT SIDE" and "SOLDER SIDE". at the time, the switch is at possition nr.2 (there is a possition nr.1 and a nr.2).

Can someone try to identify this board and find out how to get it work?

curtis
February 29th, 2008, 03:23 PM
Pictures would be useful.

per
March 1st, 2008, 02:03 AM
I got it working by pulling the switch to option nr.1.

Anyway, The Amiga I got is well used, yellowished cover, not in the best condition i've seen, but it works perfect (Workbench 1.3.3 uses years to load, but maybe that's normal). I got it with a bounch of floppydisks, most of them are cracked and/or pirated games, and a coupple are freeware/trial games. About half of the disks has read/write errors:(.

carlsson
March 1st, 2008, 06:32 AM
About half of the disks has read/write errors.
It almost sounds like the former user suffered some virus. From what I remember, some of the nasty viruses would put a lot of effort in creating read errors on your floppies. Sometimes they're recoverable, sometimes not. The disk-validator virus Saddam was one of the more devastating. However as an early form of anti-virus, there was special software to protect you from getting affected of some viruses. They would still copy themselves on your disks, but would be prevented to do any harm. I will never forget one guy in my circle of friends who gladly swapped floppy disks full of Saddam and other viruses, and excused himself with that he had protecting software so he didn't care if he infected his friends' floppy disks and computers.

per
March 1st, 2008, 08:15 AM
it's allways the same disks who gets R/W errors. If there was a virus, there would be R/W errors on all of them when read enough times, I think. BTW, how do I track viruses and how do I remove them? Is it really some writeable memory inside the Amiga that stays on when the power is off? If not, how else does the virus stay in the computer?

*Edit*
I just realized that the main disks without R/W errors are writeproteced... Does the viruses store themselves into the bootsector of the floppydisks? If so, couldn't a virus be avoided by NOT using the infected disks and by having the Amiga turned totally off before a new disk is being booted?

carlsson
March 1st, 2008, 01:49 PM
Viruses spread from floppy to floppy and yes, the floppy needs to be write enabled. There is no static memory in the computer where viruses can reside.

fred333
April 7th, 2008, 10:05 AM
Did not know that... Thanks.

barythrin
April 7th, 2008, 10:27 AM
Generally true, depending on the type of virus (bootsector/MBR/boot virus vs file infector, etc) determines how you'd be safe although it also depends on how creative the author decided to get or what they thought they could do. If it's just a boot virus (only runs when the boot sector code is executed or only runs if in the startup sequence) then you'd likely be safe as long as it has no files on your hard drive to infect and turn your computer completely off before inserting another disk.

I mostly have experience with x86 viruses not C=/Amiga, etc but the Amiga/PC equivalent will result in the virus overwriting the memory address for the interrupt/vector for disk reads with a pointer to it's own code which then it runs doing whatever it was told to and then resumes the normal disk I/O code. On a PC if it puts itself in (high memory?) it can survive a warm reboot in dos (ctrl+alt+del) although some faked this by intercepting the keyboard interrupt as well and then quickly writing themselves to the drive for next boot if they can.

Ok.. that was totally not on topic for your question lol but I felt compelled to reply. But yeah be carefull when testing the disks if there is an infected one.

- John

per
April 7th, 2008, 10:39 PM
Generally true, depending on the type of virus (bootsector/MBR/boot virus vs file infector, etc) determines how you'd be safe although it also depends on how creative the author decided to get or what they thought they could do. If it's just a boot virus (only runs when the boot sector code is executed or only runs if in the startup sequence) then you'd likely be safe as long as it has no files on your hard drive to infect and turn your computer completely off before inserting another disk.

I mostly have experience with x86 viruses not C=/Amiga, etc but the Amiga/PC equivalent will result in the virus overwriting the memory address for the interrupt/vector for disk reads with a pointer to it's own code which then it runs doing whatever it was told to and then resumes the normal disk I/O code. On a PC if it puts itself in (high memory?) it can survive a warm reboot in dos (ctrl+alt+del) although some faked this by intercepting the keyboard interrupt as well and then quickly writing themselves to the drive for next boot if they can.

Ok.. that was totally not on topic for your question lol but I felt compelled to reply. But yeah be carefull when testing the disks if there is an infected one.

- John

Happily, my Amiga doesn't have a hard drive :D