Apple II+ Flakey Inverse Characters
wrodiger
modern solid state disk hardware (CFFA or iDisk). The keyboard is
still a little flakey, but I hope usage will clear that up.
My problem is that inverse characters flicker and contain some random
bits. I have read that there is a XOR operation that is performed on
the character set to create the inverse chars, and I am hoping this
can be as simple as reseating/replacing a couple logic chips to
resolve this. Does anyone know where this logic is? Or is this done in
ROM/software?
Thanks in advance for any help,
Will
D Finnigan
>
> Thanks in advance for any help,
>
Here is a repair guide which may help:
http://macgui.com/kb/article/759
Bugman
resurrecting several apple ][+ keyboards in the past. I carefully
remove the keycap exposing the center shaft. I then drip some 90% IPA
down the post and press in several times ensuring that some IPA makes
it inside to where the switch conact is made. This is all done with
the power off. After allowing proper time to dry, I then power on the
computer and re-test. It can take several repeats before the key is
consistently fixed. I spent most of a day bringing back about 1/2 of
a keyboard. Don't get discouraged if the next day several keys need
to be re-done. This methods assumes that the problem is with dirty/
oxidized contacts. If you are just experiencing minor glitches
(occasional double characters, etc.), then you may be correct in that
they will improve with use. Others here may also have additional
opinions on what other solvents/cleaners work. 90% IPA was cheap and
worked pretty good.
wrodiger
By IPA, do you mean India Pale Ale??? That would be a new use for one
of my favorite beers!!! I get both double characters, and no chars at
all. I was wondering if some sort of electrical contact cleaner would
fix this.
Will
wrodiger
Thanks, I'll take another look through this. I reseated and swapped a
few of the IC's mentioned here to no avail the other day.
Will
AppleCPM
On Jan 4, 3:28 pm, wrodiger wrote:
> By IPA, do you mean India Pale Ale??? That would be a new use for one
> of my favorite beers!!! I get both double characters, and no chars at
> all. I was wondering if some sort of electrical contact cleaner would
> fix this.
IPA also stands for isopropyl alcohol. I'm also a big IPA fan
(the beer, not the alcohol), have you tried Mendocino Imperial IPA?
Outstanding!
Willi
Bugman
because it seeps into the tiny spaces between the posts and makes it
to the actual contact pretty easily. A contact / TV tuner cleaner
might work OK if you could get it inside. I like 90% also because I
know it evaporates with no trace very quickly. WD-40 cleans contacts
too, but that is known to leave a lubricating residue with is probalby
not best for this application either. I've fixed double characters,
and no key response this way on many keyboards. Might be worth a try
if it doesn't inprove on its own.
Michael J. Mahon
> ...I prefer the 90% alcohol
TV tuner/contact cleaner is especially made with low surface tension
so that it penetrates even the tiniest clearances to reach the contacts.
The same is true for potentiometer cleaning solutions.
The point of all of them is to dissolve soil (and contact cleaners can
also dissolve some oxides) and leave a thin protective film to delay
future oxidation. Lubricants are usually included.
Any of them work best with repeated operation (friction) of the
contacts while drying, to help abrade soil and oxides. This is
also true of "noisy" pots, which must be oscillated repeatedly from
stop to stop while the cleaner is still wet and evaporating to clear
the wiper contact and its "track" on the element and keep it clear
as the solvent evaporates. Switch contacts benefit from the same
repeated operation, for the same reason.
In fact, many dirty contacts (and pots) can be "cleaned" just by
rapid repeated operation--hundreds of times in some cases. The
self-cleaning action of good contact design clears the soil and oxide
and restores proper operation. Regular use maintains it.
-michael
NadaNet and AppleCrate II: parallel computing for Apple II computers!
Home page: http://home.comcast.net/~mjmahon
"The wastebasket is our most important design
tool--and it's seriously underused."
wrodiger
Update: I reseated all chips involved in the text display generation
to no avail. Further analysis showed bad characters in both INVERSE
and FLASH mode. I then went through the text display section of Jim
Sather's book "Understanding The Apple II" which describes the logic
at gate level (great book by the way!). Based on my analysis, I have
determined that this is likely a bad Character ROM because the bad
bits within the characters on the display are at stationary points
within the characters. By my reasoning, and looking at the bit
shifting circuitry, this points to the ROM as the source. I ordered a
replacement from arcadecomponents.com (a good source of replacement
parts). I'll post an update when I receive this replacement and test.
Will
mwillegal
A flakey 2513 was my first guess, but you indicated that it only
happened
in inverse mode. This problem should not be dependant upon mode,
though it
may be more obvious in certain modes. I had a batch of NOS 2513 chips
where
about 50% of them had this issue.
Regards,
Mike Willegal
PS
the 341-0036 character rom part listed on the site you mention is not
a 2513 and is not compatible
with early Apple II motherboards.
Michael J. Mahon
> I think that you are on the right track.
>
> A flakey 2513 was my first guess, but you indicated that it only
> happened
> in inverse mode. This problem should not be dependant upon mode,
> though it
> may be more obvious in certain modes. I had a batch of NOS 2513 chips
> where
> about 50% of them had this issue.
>
> Regards,
> Mike Willegal
>
> PS
> the 341-0036 character rom part listed on the site you mention is not
> a 2513 and is not compatible
> with early Apple II motherboards.
Sounds like it's time for a 2716-to-2513 adapter.
> On Jan 7, 9:13 am, wrodiger <wrodi...@gmail.com> wrote:
>
>>On Jan 4, 3:29 pm, wrodiger <wrodi...@gmail.com> wrote:
>>
>>
>>>On Jan 4, 1:07 pm, dog_...@macgui.com (D Finnigan) wrote:
>>
>>>>wrodiger wrote:
>>
>>>>>Thanks in advance for any help,
>>
>>>>Here is a repair guide which may help:http://macgui.com/kb/article/759
>>
>>>Thanks, I'll take another look through this. I reseated and swapped a
>>>few of the IC's mentioned here to no avail the other day.
>>
>>>Will
>>
>>Update: I reseated all chips involved in the text display generation
>>to no avail. Further analysis showed bad characters in both INVERSE
>>and FLASH mode. I then went through the text display section of Jim
>>Sather's book "Understanding The Apple II" which describes the logic
>>at gate level (great book by the way!). Based on my analysis, I have
>>determined that this is likely a bad Character ROM because the bad
>>bits within the characters on the display are at stationary points
>>within the characters. By my reasoning, and looking at the bit
>>shifting circuitry, this points to the ROM as the source. I ordered a
>>replacement from arcadecomponents.com (a good source of replacement
>>parts). I'll post an update when I receive this replacement and test.
>>
>>Will
>
>
--
wrodiger
> I think that you are on the right track.
>
> A flakey 2513 was my first guess, but you indicated that it only
> happened
> in inverse mode. This problem should not be dependant upon mode,
> though it
> may be more obvious in certain modes. I had a batch of NOS 2513 chips
> where
> about 50% of them had this issue.
>
> Regards,
> Mike Willegal
>
> PS
> the 341-0036 character rom part listed on the site you mention is not
> a 2513 and is not compatible
> with early Apple II motherboards.
>
My motherboard is a revision 7 RFI board, so I am hoping it matches...
if not, I assume I can locate the binary image and burn my own?
Will
mwillegal
EPROM would fail in a very similar way to a 2513.
Regards,
Mike Willegal
Michael J. Mahon
> That part should work in a RFI board, though it is interesting that an
> EPROM would fail in a very similar way to a 2513.
From what I can tell, the failure mode doesn't involve any particular
pattern, just random bit flips. That seems like a plausible failure
mode for both an old mask-programmed ROM and for a floating-gate EPROM.
> Regards,
> Mike Willegal
>
> On Jan 8, 10:50 pm, wrodiger <wrodi...@gmail.com> wrote:
>
>>On Jan 8, 4:20 pm, mwillegal <m...@willegal.net> wrote:
>>
>>
>>
>>
>>
>>
>>>I think that you are on the right track.
>>
>>>A flakey 2513 was my first guess, but you indicated that it only
>>>happened
>>>in inverse mode. This problem should not be dependant upon mode,
>>>though it
>>>may be more obvious in certain modes. I had a batch of NOS 2513 chips
>>>where
>>>about 50% of them had this issue.
>>
>>>Regards,
>>>Mike Willegal
>>
>>>PS
>>>the 341-0036 character rom part listed on the site you mention is not
>>>a 2513 and is not compatible
>>>with early Apple II motherboards.
>>
>>My motherboard is a revision 7 RFI board, so I am hoping it matches...
>>if not, I assume I can locate the binary image and burn my own?
>>
>>Will
-michael
Linards Ticmanis
> mwillegal wrote:
>> That part should work in a RFI board, though it is interesting that an
>> EPROM would fail in a very similar way to a 2513.
>
> From what I can tell, the failure mode doesn't involve any particular
> pattern, just random bit flips. That seems like a plausible failure
> mode for both an old mask-programmed ROM and for a floating-gate EPROM.
... and in the case of an EPROM, it might be cured by simply reburning
it. You don't even need a UV eraser.
--
Linards
wrodiger
Bingo! Works like the day it was shipped!
Damn, the Apple II is a beautiful thing... how many computers out
there can you troubleshoot in an hour with the documentation supplied
with it (reference manual circuit diagrams), pull and replace a
socketed chip, and be back in business?
The keyboard has come back to life too!!!
Long live the Apple II!
Will