[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: My Apple ][+ is now very, very sad...

Don't know if this is solved, but here is what I would do. My guess is an issue with vertical and horizontl blanking.
First, I would swap a couple of the 4 161s (D11-D14) with each other (see if the sympoms change). These chips control timing of the video signals - I really don't think you'll see an issue there, but it is basically the brains of the video system. These 161's do need a good clock to work, but the clock is an unlikely issue.
Second I would make sure that there is a signal at the inputs of R7 and R8. Kind of hard to tell exactly what is going on without an oscilloscope, but you can lift pins out of the sockets and see if the voltage or behavior changes. I think radio shack has inexpensive logic probes that will tell you if you have a signal, but I'm not sure about the utility of those things.
Third I would look at the vertical and horzontal blanking functions. Chips are C11, B11, C13, C14, A10, and A9. This is from red book rev 0 schematics, but I think all Apple IIs and Apple II plus are pretty similar. This last section is most likely the source of the problem, but you'll be better off making sure the timing section is working before going here. 

Hope this helps,

Regards,
Mike Willegal


John wrote:

That is interesting about those chips, I had always figured that after
10 years or so, all chips started to wear out a bit. Of course, the
one that is causing this problem (whichever one that may be) might of
had its lifetime shortened a bit by something like a card being
inserted while the system is on, or a temporary accidental short. Who
knows.

I myself did make a very silly mistake yesterday whilst swapping
around common 74LSxxx chips. I was removing a 74LS257, one that is
right under the powersupply connector, next to the first slot. Due to
its awkward location, my chip extractor grabbed the whole socket
instead of just the chip, and out it came. Not a huge problem, just a
minor setback requiring a trip to my local electronics store to get a
new 16pin socket as well as a bit of soldering time. Oh well, mistakes
are inevitable, but I am determined to get this thing running once
again!

John

PS- Tristan- I'll get that email to you as soon as I made a few
modifications to it.

On Jul 15, 6:05 am, Tristan Mumford <xtristan.xmumf...@xgmail.xcom>
wrote:


Michael J. Mahon wrote:


John wrote:


<snip>


Originally, it was thought that ICs would have a "bathtub shaped"
failure rate curve, but data indicates that the "end of life"
upswing isn't there--at least for values several times their
predicted lifetimes.


So true. Especially when the ICs are powered by a nice reliable power supply
free of spikes and other anomalies.
Speaking of which I wonder how healthy the -5v rail is on the ailing II+
power supply.

Call me mad if you will, but does anyone else see the pattern of horizontal
offsets and shades on the screen. I don't think enough is being read into
that. I haven't studied the schematics too closely (even though I do need
to, to resurrect an ailing II+ Clone). It could be anything from something
obtuse like one of the MSB bits on a counter shorting to earth to a
marginal supply being overloaded by too many active gates at one time.

I know I'm not being too helpful, but a few more suggestions into the mix
couldn't hurt.

To the OP: If you happen to have the spreadsheet of components etc. still,
could I please get a copy from you? My e-mail is
xtristan_d0t_xmumford_at_xgmail_d0t_xcom with 'x's removed and punctuation
substituted of course :)

Tristan.

--
----->http://members.dodo.com.au/~izabellion1/tristan/index.html<-----
=====       It's not pretty, it's not great, but it is mine.       =====