What happened to my A500?

[darksun9210]

So my rev 5 A500 with 3.1 rom, only has one jumper lead:-
from pin 21, to pin 31 on the legs on rom chip itself, with the leg of pin 31 of the chip bent out so it does NOT go in the socket.

now, as far as i can figure, on the rev5 socket:-

pin 01 - Address 17
pin 21 - 5Volts VCC
pin 31 - BYTE-WORD select?

on the chip:-

pin 01 - Address 17/18
pin 21 and 31 are VCC 5Volts.

this may help tracing :- https://www.amigapcb.org/ i know they only have the rev8 A500 board, but it's been enough for me to trace lines and figure things out previously.

so it sounds like something got a dose of 5 volts where it doesn't want it... i hope you can find it, and its an easy fix!
it would just double check my working - i'm about 3 whiskeys in so far this evening.  but it sounds like Address17/18 got a jolt.  i hope you've got a spare 68k chip , agnus and gary chip to swap out to test? give each of them the sniff test see if the magic smoke has come out...

[darksun9210]

no worries. i feel more trepidation than elation opening the lids on these beasties these days too!

a quick note on what i understand about that rev8 board that's on PCB explorer.
its a 42pin rom socket, and the chip is a 40 pin. so you shuffle the chip back in the socket, one away from the notch end. So pin 2 of the socket goes to pin1 of the chip, then pin3->pin2 and etc. etc. and the pin count goes like that all the way round.
so on PCB explorer, ignore the top two pins, 01 and 42, and reduce the pin number of the number your looking at, by one. hope that made sense.

i'd start with buzzing out traces first off. make sure no lines have been toasted

from what i can see, pin01 on the rom socket goes to pin42 on the CPU and edge connector one way across the board, and then pin77 of Agnus and pin 34 on Gary going the other way - terminating at resistor pack RP105. So not too far.

[darksun9210]

Fair enough. i'd do the same.
that'll teach me to not pay attention to my own rev5 board though re- RP105! lesson learnt there for me. woopsy!

[darksun9210]

yeah unfortunatly in this case. if you ignore the top two pins on the socket and move everything down one, as the rev8 has a 42 pin socket, and the rev5 has a 40pin socket/rom...