Re: ROM chip test

[dempson@actrix.gen.nz (David Empson)]

<bobryan9@my-deja.com> wrote:

> I have a ROM chip which appears to be bad.  When the board is plugged
> into slot 2 and I list $c200-$c2ff in the monitor, i get:
> 
> ldy ao
> ldy ao
> ldy ao
> brk
> brk
> ldy ao
> lda ao

In other words A0 A0 A0 A0 A0 A0 00 00 A0 A0 A0 A0

This sort of pattern is common when reading areas that have no memory
present.

> lots of other crud.  This is the same as I get when I have no card in
> the slot.  Can I stick the ROM chip on another board and test it out?

Probably, assuming you can find a card which uses the same type of ROM
chip.  Even then, most cards with larger ROMs have different internal
memory organisations, so you might not see the same area of the ROM that
you would see when the ROM is placed in its normal card.

> A mouse card or disk II card, or another common apple II card? 

Not a Disk ][.  I don't know what ROM size are used on the mouse card
and the RamFactor.

Even if they use the same type of ROM chip, I don't think this would be
a good idea.  The Mouse card has its own microprocessor (a 6805) and the
ROM on the card probably contains code which is executed by that
processor at startup.  Very strange things could happen (including
possible damage to the board) if you have the wrong firmware in the
mouse card.

> I am thinking maybe it could be another part of the board that is bad.

That seems more likely.  The problem is most likely to be a corroded
track on the board, a dry solder joint, or gunk buildup in a socket
which is preventing a chip from functioning correctly.

The next most likely would be a faulty logic chip in the address
decoding circuitry, or the data bus buffer chip not working, or the ROM
being faulty, or a damaged component.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand