Re: Apple IIpluse motherboard problem

["Roger Johnstone" <rojaws@mac.com>]

In article <u6j2i1dsj1dgb0@corp.supernews.com>, russotto@grace.speakeasy.net
(Matthew Russotto) wrote:

> In article <1d8358aae4041a6c7eba504d546064b0.10725@mygate.mailgate.org>,
> Vince Briel <vbriel@yahoo.com> wrote:
>
>>I can understand the 6502 not running, but I swapped it with a working
>>one and it does the same thing.  The 6502 from the non-working board
>>works great in the known working ][plus.
>
> I'm not saying there's something wrong with the 6502, only that it
> sounds like it isn't running at all.  Shorting the phase lines can
> do that (found out the hard way), as can a lot of other things.  But the
> first thing I'd look for is a problem with the power-on reset
> circuitry.  IIRC, the 6502 just won't run without an initial reset.

If you have a volt meter you can do some simple checks. With the negative
lead on the negative supply (pin 1) of the processor you should be able to
measure +5 volts at the supply pin (8). The reset pin (40) should be at +5V
too, it's pulled low to 0V to reset the CPU.


>>Could the 555 timer chips cause the problem?  Or the crystal? I'd like
>>to get this board running to have a spare onhand.
>
> Can't be the crystal, or you wouldn't have video.

The 555 timers aren't used for anything important, one is used to generate
the keyboard auto repeat, the other is used for flashing text.

--
Roger Johnstone, Invercargill, New Zealand

Apple II - FutureCop:LAPD - iMac Game Wizard
http://homepage.mac.com/rojaws
________________________________________________________________________
"There is no reason for any individual to have a computer in their home"

   Ken Olson, President of DEC, World Future Society Convention, 1977