Re: Apple II Minus Question

[Rubywand <rubywand@swbell.net>]

Bryan Parkoff writes ...
> 
>     I would like to know Apple II Minus history that it is the earliest
> model that it starts with Old Monitor Routines rather than AutoStart
> Routines.  Do white horizontal block like GR (low resolution) appears in the
> screen?  Or...Do white horizontal block like TEXT ("@@@@" and "??????")
> appears in the screen?
>     If it is GR, must you always press RESET before it returns to "*"
> prompt?
>     First, you turn on Apple II Minus.
>     Second, odd lines (1, 3, 5, 7, 9, etc) appears "@@@@@@@@" and even lines
> (2, 4, 6, 8, 10, etc) appears "????????".  They are all inverse.
>     Third, "*" prompt appears in 24th line.
> 
>     Sometimes, "???>@.?1??<??" show.  Do you suspect that it may be bad RAM?
> Or it may be static leakage?
> 
>     Are all "00 00 00 00 00 00 00 00" store in odd pages between $0000 and
> $BFFF and "FF FF FF FF FF FF FF FF" store in even pages between $0000 and
> $BFFF?  If each page do show like "01 01 01 01", "7F 7F 7F 7F", "E1 E1 E1
> E1", "FE FE FE FE", or etc.  I claim that all static RAM chips are bad.  It
> is why I have Apple II Minus and Apple II Plus motherboards that are
> defective in my hand except extra Apple II Plus is working OK.
> 
>     I bought all 7xxxx chips and RAM chips from electronic store.  I removed
> all old chips out of all sockets.  I threw them in the trash.  I put new
> 7xxxx chips and RAM chips in all sockets.  I did test, but the result is
> still the SAME.  Such as GR and HGR are not working (never turn on, but stay
> in TEXT only).
>     It may be motherboard that is bad.  Probably some resistors, capicators,
> and other electronic parts are bad however all chips are working fine on
> another Apple II+ motherboard.  I do have Apple II+ repair manual.  It does
> provide me a lot of information, but it does not specify where defective
> occurs.  It suggests to use electronic diagnostic tools to measure voltage,
> resistors, currents, etc on the motherboard.
>     Please suggest which electronic diagnostic tools that is very worth for
> me to buy before I can be able to isoslate defective parts.  If I have found
> defective, I would be ABLE to repair.  Please advise.
> 
 ....

     The best diagnostic tool is usually the computer itself-- you try
different things and notice what it does.

     Maybe some RAM interface IC is loose or defective. Try pulling and
cleaning the pins of the 74LS174's at B5 and B8 (near the front of the
motherboard). Do the same for the 74LS257's at B6 and B7.

     If that doesn't fix things, try pulling and resocketting every IC. It's
pretty common for old computers to develop problems due to loose IC's or IC's
which have developed corrosion on pins. (Out II+ did that about a month ago.
Pulled and cleaned the IC's and the II+ has been working fine since.)



Rubywand