1977 original apple II restoration (continued)...

[Nama]

So I just got the motherboard back from the board repair shop (they
removed some hacked wires and fixed a couple of damaged traces to bring
the machine back to original condition).

Now it's up to me to actually get the machine working...

Firstly I swapped out all the RAM for some that I recently purchased,
in the hopes that the old RAM was bad (of course I do not know this to
be true). The problem now is that on 'power up' I get 10 vertical white
bars across the screen. Pushing reset does nothing.

I spent a good deal of time swapping out ALL the ic's (what a painful
job that is), one at a time (including CPU and ROM's) from a ][+
motherboard last night.
After swapping in and out all the chips I still saw absolutely no
change in the 10 vertical bars.
However, I do suspect that the ][+ motherboard I was using for spares
is also dead, but I figured that the chance of the same component being
faulty in the two systems was slim.

I then swapped all the old ram back in, and only then did I see any
change in the screen. The pattern displayed was exactly the same as it
was befor the hacked wire removal and the trace fix. You can see the
pictures of this screen that I had previously taken here (reset still
does nothing):

http://homepage.mac.com/lord_philip/PhotoAlbum18.html

So basically, after the board fix with all the original ic's and RAM in
place there is no change to the screen as previously seen. Replcaing
the RAM, changes the screen to vertical bars.

So, now I'm stumped. Does anyone have any insights.

I have looked in the archives, and have seen reference to other users
experiencing 10 vertical lines but the solution to this problem is
unclear. Most suggestions recomend swapping the ROM's or CPU, which I
have already done.

Cheers

Phil

[schmidtd]

I had a different kind of video problem with a board of mine. But like
you, I saw some real characters. So I figured the video circuitry was
good, so was character ROM, so was at least some memory, and the CPU
was probably ticking too. I also went through the process of swapping
and testing each and every socketed IC. No dice. Mine turned out to
be one of the transistors - the 3904 between A and B, 12 and 13.

I'd replace the transistors on the board. Desolder and solder in new
parts. You can get them from Radio Shack or Jameco.

[sicklittlemonkey]

> So, now I'm stumped. Does anyone have any insights.

Perhaps someone else here can offer better insights based on the
symptoms, and certain frequenters of this group can most *definitely*
expand on my suggestion below.

You've popped the chips and jiggled things around ... it's time to find
out which subsystems are operating, and which aren't. You should buy a
cheap logic probe if you don't already have one, read a tutorial on
using it (which I presume you need to do, since you're asking for more
help) like this one here I googled up:
http://users.erols.com/mowerman/logicprobe.htm

Whether you want to play with this first on your original Apple II is
up to you, but I'd skill up on an expendable board first just to get
more comfortable. This isn't rocket science though, and you're pretty
unlikely to screw up boards using just a logic probe.

You know video of some kind is being output, so I'd start with the CPU.
Check the voltage, clock inputs, ensure RESbar is being pulled high
(likewise other interrupts), then see if any of the address lines are
toggling.

Your machine is not going "beep", so working back from the CPU will
eventually lead you to the subsystem that's stuck.

Cheers,
Nick.

[j...@cimmeri.com]

Hi Phil,

What I would do (and have done in your situation) is start with
another working motherboard... a II+ board would be fine. Make sure
it works. Then take 5-10 parts at a time from your II board --
starting with the ROMs -- and transplant those into the working board
-- testing each time with a power on to be sure that the transplanted
parts are working correctly.

If the test board stops working after a transplant, you'll have to
go back and narrow down further to find which parts aren't working.

If you find that all the ICs are working upon transplant, then
you'll be in more trouble. At that point, I would still suspect a
socket problem on the original board. They often are quite oxidized
and it can take many inserts of a dummy chip and some sprays of a
deoxing agent to get them flowing electrons again.

Only after sockets, would I then start testing each passive
component.. for that you'll need a variety of testers.. BUT.. I've
worked on many of these II's and have not yet encountered a passive
component failure.. so though it happens, it's not the most likely
explanation.

~ J

[Liam Busey]

Nama wrote:

-snip unresponsive rev 0 Apple 2 problems-

Hi Phil, just for giggles plug in a Disk II card and see if you get a
beep or a monitor prompt. It could be something simple like your
keyboard reset switch/ line isn't working.

Liam

[Michael J. Mahon]

Nama wrote:
> So I just got the motherboard back from the board repair shop (they
> removed some hacked wires and fixed a couple of damaged traces to bring
> the machine back to original condition).

You probably removed a shift-key mod, etc... ;-)

> Now it's up to me to actually get the machine working...
>
> Firstly I swapped out all the RAM for some that I recently purchased,
> in the hopes that the old RAM was bad (of course I do not know this to
> be true). The problem now is that on 'power up' I get 10 vertical white
> bars across the screen. Pushing reset does nothing.

Don't worry, the original RAM is almost certainly not bad.

You could have removed all but the first bank (the row nearest the
processor) and tested with 16KB. You could then substitute from the
pool of 16 chips you removed with a virtual certainty of not finding
*two* bad DRAM chips.

It sounds like your processor is not actually resetting.

> I spent a good deal of time swapping out ALL the ic's (what a painful
> job that is), one at a time (including CPU and ROM's) from a ][+
> motherboard last night.
> After swapping in and out all the chips I still saw absolutely no
> change in the 10 vertical bars.
> However, I do suspect that the ][+ motherboard I was using for spares
> is also dead, but I figured that the chance of the same component being
> faulty in the two systems was slim.

That's a good assumption.

> I then swapped all the old ram back in, and only then did I see any
> change in the screen. The pattern displayed was exactly the same as it
> was befor the hacked wire removal and the trace fix. You can see the
> pictures of this screen that I had previously taken here (reset still
> does nothing):
>
> http://homepage.mac.com/lord_philip/PhotoAlbum18.html
>
> So basically, after the board fix with all the original ic's and RAM in
> place there is no change to the screen as previously seen. Replcaing
> the RAM, changes the screen to vertical bars.
>
> So, now I'm stumped. Does anyone have any insights.
>
> I have looked in the archives, and have seen reference to other users
> experiencing 10 vertical lines but the solution to this problem is
> unclear. Most suggestions recomend swapping the ROM's or CPU, which I
> have already done.

What you are seeing (the bars) is a random pattern in video RAM, which
demonstrates that the RAM is at least "sort of" working, and the video
generator is working. The processor is not working, since it is not
resetting. (An early Apple ][ should not require holding CTRL while
pressing RESET, but you might try it.)

Failure to reset is a very fundamental problem. It can be caused by
the /RESET signal not reaching the processor or by the 1MHz clock
signal not reaching the processor.

If the processor is getting clock and /RESET, then it must be unable
to access memory/ROM properly, or the F8 ROM may be faulty. There
are tranceivers in the path to the ROM address lines and the path
from ROM data to the processor. They are three 8T97's and two 8T28's
in board locations H3, H4, and H5, and locations H10 and H11. These
chips can be damaged by inserting or removing a peripheral card while
the system is powered on, or by ESD when it is off.

The fact that you have replaced these chips is a strong probabilistic
argument agains them being the problem, but it might be worth another
try (just for them).

You should also take a *very* close look at the board traces to
verify that there are no tiny cracks or cold solder joints that
could disrupt signal propagation. A low-power (VOM-type) continuity
tester can be useful in this process--do *not* use a continuity
tester that uses an incandescent bulb or more than a single cell
battery!

If these techniques don't localize the problem, I'm afraid it may
be time to get out an oscilloscope and start signal tracing.

-michael

Music synthesis for 8-bit Apple II's!
Home page: http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it is seriously underused."

[Michael J. Mahon]

All good ideas, and easier than putting a scope on it. ;-)

[Michael J. Mahon]

I agree. The only passive failure I've encountered was a 0.1uF bypass
capacitor near the processor (which caused intermittent failures about
every ten seconds!), but it was actually caused by repeated flexing
which caused a hairline break in one lead. (Too much Zip Chip insertion
and removal. ;-)

[Nama]

Thanks guys,
Obviously there is a lot to think about, and probably a lot of new
things to learn.
Not knowing to much about electronics, I think I will start with the
swap idea that J suggested...if that doesn't work then I'll be forced
to move on to a more technical solution.

Thanks again

Phil

[sicklittlemonkey]

Hi Phil.

Looking at your original post again, it is very strange that your
original problem restored itself *only* when you replaced the original
RAM. If the stack RAM was hosed, the CPU might spin endlessly, but with
either set of RAM, there was no beep right?

So RAM is likely fine as Michael suggests - the CPU is not getting
something it needs. You've swapped everything once, so if you're going
to do it again, start with Michael's suggestions below (currently post
#10) and perhaps do the continuity tests while you're doing the swaps.

After that, honestly, a logic probe (which is much simpler and cheaper
than a scope - we're talking less than $20 back in NZ, 3000 Yen at most
here, surely) is really easy to use. You just poke it somewhere, like
the CPU's reset pin, and it tells you if it's high (~+5V) or low (~0V)
or oscillating.

Cheers,
Nick.

[Michael J. Mahon]

sicklittlemonkey wrote:
> Hi Phil.
>
> Looking at your original post again, it is very strange that your
> original problem restored itself *only* when you replaced the original
> RAM. If the stack RAM was hosed, the CPU might spin endlessly, but with
> either set of RAM, there was no beep right?

The difference is likely just the "random" power up state of the
DRAMs, which is displayed on the screen.

Upon RESET, the first thing the II does is set a couple of flags in
memory, then set text mode, which clearly isn't happening from the
look of the display. This all happens about a dozen instructions into
RESET, so the processor isn't making much headway...

[sicklittlemonkey]

> The difference is likely just the "random" power up state of the
> DRAMs, which is displayed on the screen.

Yeah, you're right. I was suspicious of one of Phil's startup screens
which is mixed (shows text and GR), but startup allows that, I suppose.

> Upon RESET, the first thing the II does is set a couple of flags in memory

Yes, but both RES and IRQ/BRK use JSR, which is why I mentioned bad
stack RAM being a possible cause. It's pretty much ruled out by the RAM
chip swap, though.

I hope the repeat chip swap doesn't magically solve this, because I'm
kinda looking forward to hearing what is stopping the CPU. ;-)

Cheers,
Nick.

[Jorge Chamorro]

schmidtd <schm...@my-deja.com> wrote:

That is the transistor that drives the /RESET line.
It is the perfect candidate in this case.

CHECK /RESET !

First unplug the keyboard cable connector and then check the voltage
there (in the keyboard connector, on the MLB, with the keyboard cable
unplugged) between pins 8(GND) and 3(/RESET) :

1---v---16
2- -15
red tester probe here-->3- -14
4- -13 <- KEYBOARD CONNECTOR ON THE MLB
5- -12
6- -11
7- -10
black tester probe here-->8-------9

If there are (close to) +5v, jumper (short) somehow pin 8 with pin 3, to
manually "feed" a reset. If it still does not work, the problem is
likely somewhere else, nor related to /RESET. Well, you should first
check too for continuity between pin 3 on the MLB keyboard connector,
and pin 40 on the processor, just to make sure that the 6502 is getting
the /RESET too.

If there are 0.x volts, then the transistor is most likely bad, or it is
being (badly) driven on by the power up reset circuit, the 555 at A13.

To check the transistor without removing it, first remove the 555 at
A13, then jumper somehow pin 3 to pin 1 on the now empty 555 socket at
A13. Turn it on and check again the voltage in the keyboard connector
(as above), it should be (close to) +5V. If it is 0.x V, the transistor
is most likely bad. I say most likely because there remains the
possibility of a short in the /RESET line, somewhere else. BTW, if
you've got some business cards nearby, insert one in each slot
connector, just to make sure they are not shorting. I've seen more that
one Apple II with the pins bent inside the slot connector, shorting
inside the connector with the pin just in front of it.

If you feel the transistor is bad, remove it by first cutting the legs,
connect everything in place and try to make the Apple II work by
manually feeding a /RESET, this time from the RESET key on the keyboard.
This way, without a reset circuit, it's more like a real original Apple
II, I think.

It's of no use to check any further without making sure first that
/RESET is not stuck low. So let us know... GOOD LUCK !

[Nama]

Thanks for everyones help.

Apple II is !00% up and running.

Phil

[Michael J. Mahon]

Nama wrote:
> Thanks for everyones help.
>
> Apple II is !00% up and running.

So, what exactly was the problem?

[Ralph Hyre]

I don't know if I agree with this plan - replacing one chip at
a time is a better approach.

>Then take 5-10 parts at a time from your II board --
>starting with the ROMs -- and transplant those into the working board
>-- testing each time with a power on to be sure that the transplanted
>parts are working correctly.

I once loaned my disk ][ card to a fellow Apple ][ user in my dorm.
He was building hardware, and when I got the controller back I noticed
my system wasn't booting anymore.

He fried a 7405 on the Disk ][ card, which was pulling RST low
on the 6502, and never letting go. I used a logic probe, but not for
very long before the problem was obvious. My hazy recollection is
that RST was run to the keyboard encoder board, so there were very
large pins.

I was able to troubleshoot by noticing the machine, and diagnose the
blown chip. (Imaging trying to do chip-level repair today!)

Anyway, I replaced the blown chip, and was going again.

The oldest schematics I have are from the Apple ][+, not the ][.

As I recall, you had to manually push the 'Reset' button to get the
original
Apple ][ going, since they didn't have autostart ROMs or other more
modern
conveniences.

If you have a low enough serial number, your keyboard will have N-key
rollover,
which is a think of beauty compared to the 2-key rollover on the ][+
and later models.

Have fun,

- Ralph Hyre

[Michael J. Mahon]

Ralph Hyre wrote:

<snip>

> The oldest schematics I have are from the Apple ][+, not the ][.

The Apple ][ is the same hardware machine as the Apple ][+. The
only difference is the autostart ROM and Applesoft in ROM.

There were keyboard encoder changes along the way, but late model
]['s were changed, too.