RE: 6540 ROMs replacement ?

From: Jürgen Sievers (
Date: 2003-02-04 22:20:41

> -----Original Message-----
> From:
> []On Behalf Of Nicolas Welte;
> address is valid for replies (Re:) only!
> Sent: Tuesday, February 04, 2003 9:05 PM
> To:
> Subject: Re: 6540 ROMs replacement ?
> Jürgen Sievers wrote:
> > Some pins a broken and after I have soldered a socket unter the
> ROMs they
> > continue not in working condition. Some times aftyer power on the normal
> > prompt appear but most some random is spread over the whole screen.
> it seems you have a contact problem. I have the same in one of my
> PETs, and
> since I didn't want to install new sockets, I just put a precision socket
> under each ROM and plugged that into the original socket. It helped.

hat's what I did but it doesn't help.

The sockets installed are very sheap and so the new sockets could not fit
into the old sockets.
The renewed only touches the side of the top parts from the old sockets. But
without much pressure and so some pins don't getting into contact. I can't
press the new sockets into the old sockets deep enough.

> I have made a 6540 adaptor, but it is a simplified design that
> only works in
> the character ROM socket. I did this because the support of three
> (or even
> four?) chip select inputs would require an extra logic chip. If
> you look at
> the layout you will see that the 6540 pinout is very different
> from 25xx or
> 27xx series EPROMs. The schematics (Eagle format) also show the
> pinouts of
> the 6540 and 6550.
> For replacing all the system RAM and ROM I designed another circuit that
> plugs directly into the 6502 socket. You can read about both devices here:
> Nicolas
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