30 Nov
2015
30 Nov
'15
3:18 p.m.
Speaking of Schrodinger's feline, here are details of my recent Apple II+
repair for those who might be interested:
http://www.classic-computers.org.nz/blog/2015-11-29-more-repairs-to-my-appl…
Terry (Tez)
30 Nov
30 Nov
3:44 p.m.
On 11/30/2015 02:18 PM, Terry Stewart wrote:
Speaking of Schrodinger's feline, here are details
of my recent Apple II+
repair for those who might be interested:
http://www.classic-computers.org.nz/blog/2015-11-29-more-repairs-to-my-appl…
Nice!
My II+ needs a new escape keyswitch, keycap and encoder IC, just in case
anyone reading this ever happens to be parting out a US-spec system (I'm
guessing that a Europlus or J-plus encoder is very slightly different. Was
also led to believe that there are a couple of different keycap styles for
US-spec systems).
The keycap's probably the critical thing - I think there may be other
sources for the switches (at least there were until a few years ago), and I
suppose that a PIC-based approach via a small plug-in carrier board would
be an option for the encoder if needed, although it would be nice to keep
the machine original if possible.
cheers
Jules
5:20 p.m.
On 11/30/2015 12:18 PM, Terry Stewart wrote:
Speaking of Schrodinger's feline, here are details
of my recent Apple II+
repair for those who might be interested:
http://www.classic-computers.org.nz/blog/2015-11-29-more-repairs-to-my-appl…
Terry (Tez)
Terry,
nice dialog on your repair job.
On the last comment about the ground pin of the defective rom having a signal, if the
apple board is a 4 layer board the ripple from the short to the internal signals from
address current, or other signal current being propagated to the ground pin, I suspect the
resistance in the pin itself may have provided the needed high resistance to show the
signal. Unless you scrap the ground solder protect off and look at the voltage out in the
actual ground conductor, I suspect the voltage went down to a very low level very close to
the pin.
Also where were the decoupling capacitors located with respect to the pin. I suspect that
might have gotten rid of more of the voltage, but they were probably nearer the Vcc end of
the chip.
If you can track down the schematic, it might be that your missing pin doesn't do much
unless you perform some special operation, such as some controller addressing or memory
operation or such that you don't normally do. It may have also had a fit to the other
part of the pin if it was present in the socket to actually work. I didn't hear if
you found that, or maybe it fell off when you pulled the chip out?
I suspect the short developed from your theory about stress, or perhaps the chip was
programmed by a bad programmer. We had a programmer that we found developed a tendency to
program eproms and like programmable chips and it destroyed the chips capability to
actually reach ground again.
The programmer made chips that verified, but when you ran them in a circuit and probed the
lines with some sync to the system clock, rather than seeing the signals on the data lines
going to zero on the datalines, you could see a hodgpodge of crap at 1.5 to 3 volts which
is TTL la-la land. The chips programmed in such a programmer as a properly working Data
I/O had clean lines as did reference chips from years earlier.
Due to the fact we didn't program many chips, and I found a cheap programmer to hook
to a PC, we never found out what broke in our programmer (which was a home design
admittedly). But it was build to standard, but had something happen to start killing
eproms. So that sort of fault may have been induced in your chip and got bad enough to
kill off your Apple some years later.
thanks
Jim
6:22 p.m.
Thanks for those comments Jim, Yes, something to think about.
Peter Coghlan dropped me a note privately, saying the signal of the F8 ROM
could also be caused by the pin not connecting properly. The replacement
ROM could have had been sufficiently different in that the legs were at a
slightly different angle etc. This would also make sense, as I couldn't
understand why their wasn't anything on the earth rail (and why the PSU
didn't shut itself off).
So, there could be a socket problem still lurking which may come back to
haunt me later so I'll check it out at some stage (In fact, I might just
replace the socket). I'll have to fish that F8 ROM out of the rubbish bin
and try it in another working Apple board. I did put it back in the first
board at the time just as a double check and got the same result as before
so I concluded it was toast.
Terry (Tez)
On Tue, Dec 1, 2015 at 11:20 AM, jwsmobile <jws at jwsss.com> wrote:
On 11/30/2015 12:18 PM, Terry Stewart wrote:
Speaking of Schrodinger's feline, here are
details of my recent Apple II+
repair for those who might be interested:
http://www.classic-computers.org.nz/blog/2015-11-29-more-repairs-to-my-appl…
Terry (Tez)
Terry,
nice dialog on your repair job.
On the last comment about the ground pin of the defective rom having a
signal, if the apple board is a 4 layer board the ripple from the short to
the internal signals from address current, or other signal current being
propagated to the ground pin, I suspect the resistance in the pin itself
may have provided the needed high resistance to show the signal. Unless
you scrap the ground solder protect off and look at the voltage out in the
actual ground conductor, I suspect the voltage went down to a very low
level very close to the pin.
Also where were the decoupling capacitors located with respect to the
pin. I suspect that might have gotten rid of more of the voltage, but they
were probably nearer the Vcc end of the chip.
If you can track down the schematic, it might be that your missing pin
doesn't do much unless you perform some special operation, such as some
controller addressing or memory operation or such that you don't normally
do. It may have also had a fit to the other part of the pin if it was
present in the socket to actually work. I didn't hear if you found that,
or maybe it fell off when you pulled the chip out?
I suspect the short developed from your theory about stress, or perhaps
the chip was programmed by a bad programmer. We had a programmer that we
found developed a tendency to program eproms and like programmable chips
and it destroyed the chips capability to actually reach ground again.
The programmer made chips that verified, but when you ran them in a
circuit and probed the lines with some sync to the system clock, rather
than seeing the signals on the data lines going to zero on the datalines,
you could see a hodgpodge of crap at 1.5 to 3 volts which is TTL la-la
land. The chips programmed in such a programmer as a properly working Data
I/O had clean lines as did reference chips from years earlier.
Due to the fact we didn't program many chips, and I found a cheap
programmer to hook to a PC, we never found out what broke in our programmer
(which was a home design admittedly). But it was build to standard, but
had something happen to start killing eproms. So that sort of fault may
have been induced in your chip and got bad enough to kill off your Apple
some years later.
thanks
Jim
6:52 p.m.
Peter Coghlan dropped me a note privately, saying the
signal of the F8 ROM
could also be caused by the pin not connecting properly. The
replacement
ROM could have had been sufficiently >different in that the legs were at a
slightly different angle etc. This would also make sense, as I couldn't
understand why their wasn't anything on the earth rail (and why the PSU
didn't shut >itself off).
Incidentally, I did check when the machine was off to see if that F8 earth
pin did connect to ground. It appeared to, but then I was putting some
pressure on the pin when I was taking the measurement. It might have been
enough to force a connection in the socket.
Terry (Tez)
On Tue, Dec 1, 2015 at 12:22 PM, Terry Stewart <terry at webweavers.co.nz>
wrote:
Thanks for those comments Jim, Yes, something to
think about.
Peter Coghlan dropped me a note privately, saying the signal of the F8 ROM
could also be caused by the pin not connecting properly. The replacement
ROM could have had been sufficiently different in that the legs were at a
slightly different angle etc. This would also make sense, as I couldn't
understand why their wasn't anything on the earth rail (and why the PSU
didn't shut itself off).
So, there could be a socket problem still lurking which may come back to
haunt me later so I'll check it out at some stage (In fact, I might just
replace the socket). I'll have to fish that F8 ROM out of the rubbish bin
and try it in another working Apple board. I did put it back in the first
board at the time just as a double check and got the same result as before
so I concluded it was toast.
Terry (Tez)
On Tue, Dec 1, 2015 at 11:20 AM, jwsmobile <jws at jwsss.com> wrote:
On 11/30/2015 12:18 PM, Terry Stewart wrote:
Speaking of Schrodinger's feline, here are
details of my recent Apple II+
repair for those who might be interested:
http://www.classic-computers.org.nz/blog/2015-11-29-more-repairs-to-my-appl…
Terry (Tez)
Terry,
nice dialog on your repair job.
On the last comment about the ground pin of the defective rom having a
signal, if the apple board is a 4 layer board the ripple from the short to
the internal signals from address current, or other signal current being
propagated to the ground pin, I suspect the resistance in the pin itself
may have provided the needed high resistance to show the signal. Unless
you scrap the ground solder protect off and look at the voltage out in the
actual ground conductor, I suspect the voltage went down to a very low
level very close to the pin.
Also where were the decoupling capacitors located with respect to the
pin. I suspect that might have gotten rid of more of the voltage, but they
were probably nearer the Vcc end of the chip.
If you can track down the schematic, it might be that your missing pin
doesn't do much unless you perform some special operation, such as some
controller addressing or memory operation or such that you don't normally
do. It may have also had a fit to the other part of the pin if it was
present in the socket to actually work. I didn't hear if you found that,
or maybe it fell off when you pulled the chip out?
I suspect the short developed from your theory about stress, or perhaps
the chip was programmed by a bad programmer. We had a programmer that we
found developed a tendency to program eproms and like programmable chips
and it destroyed the chips capability to actually reach ground again.
The programmer made chips that verified, but when you ran them in a
circuit and probed the lines with some sync to the system clock, rather
than seeing the signals on the data lines going to zero on the datalines,
you could see a hodgpodge of crap at 1.5 to 3 volts which is TTL la-la
land. The chips programmed in such a programmer as a properly working Data
I/O had clean lines as did reference chips from years earlier.
Due to the fact we didn't program many chips, and I found a cheap
programmer to hook to a PC, we never found out what broke in our programmer
(which was a home design admittedly). But it was build to standard, but
had something happen to start killing eproms. So that sort of fault may
have been induced in your chip and got bad enough to kill off your Apple
some years later.
thanks
Jim
3159
days inactive
3159
days old
4 comments
3 participants
participants (3)
-
jules.richardson99＠gmail.com -
jws＠jwsss.com -
terry＠webweavers.co.nz