Re: Who can I send my Apple II card to for Repair?

[dempson@actrix.gen.nz (David Empson)]

TWS <adoyson@nccn.net> wrote:

> The GROUND/+5V connectors are at the BACK of the slot connector, correct?

Yes.  Pin 25 is +5V, pin 26 is ground.  The other power supply pins are:

33  -12V
34  -5V
50  +12V

A short on any of these pins might be causing the power supply to shut
down. 

In a later followup you mentioned covering up the +5V and ground pins.
This is not a good idea, because having ground unconnected means that
there is no reference voltage for any of the circuitry on the card, and
all sorts of weird things could be happening.

It is also not a good idea to try to run the card with ground but not
+5V connected, because ICs generally don't like having voltages on their
inputs but no power supply.  The signal lines tend to get heavily
loaded.

In any case, it doesn't necessarily prove a short between +5V and ground
- it might be one of the other supply rails, but there is no connection
because you've left ground detached.

It still seems most likely that it _is_ between +5V and ground, as the
card probably isn't using the other rails.

> Those pins are nearest the back of the computer?

Yes.  Pins 1 to 25 are on the front of the card, 26 to 50 on the back,
thus +5V is the pin closest to the back of the computer on the front of
the card, and ground is the corresponding pin on the other side of the
card.

> IF SO:  theres' something _really strange_ about this card.  The ground is
> connected to a Capacitor.......the other lead of the Capacitor goes to
> +5V.........??????  DEAD short?  That is exactly what is happening (if the
> Ground/+5v pins are located where I think they are)  However, I find this hard
> to believe because there have been no modifications to this area of the board.

This is quite normal.  Every card should have a 10 microfarad capacitor
going between the +5V and ground lines, or something equivalent, and it
should be very close to the slot connector.  It provides a local charge
reservoir for dealing with bursty power usage on the card, and helps to
weed out glitches in the power supply from the motherboard.

A capacitor has no electrical contact between its two pins.  They use
the principle of an electric field between two plates (or something
similar), storing a charge.  The capacitor tends to resist changes in
voltage: a sudden dip in the +5V rail will be smoothed out by the
capacitor discharging a little.

Most cards also have a decoupling capacitor next to most if not all ICs.
These are used in a similar way, for supplying bursty current
requirements of individual chips.

Note that if a capacitor has developed a fault, it might be shorting out
the power supply.

> NOTE:  I am guessing that these are capacitors.  They are orange Ceramic
> looking blobs.  They are labeled on the board as "C-XX"  where XX is a number.

Yep, that sounds like a capacitor to me.

> 106  +25  K           is what the (??capacitors??)  are labeled  (on the
> component).  The K is both UNDERLINED___  and there is also an "overline"
> 
> -
> k            <----------  kinda like that
> -

Possibly a brand marker?  (I've seen it, but never investigated what it
means.)  The key piece of information is "106", which represents "10
times 10 to power of 6", i.e. 10,000,000 picofarads, or 10 microfarads.
The +25 refers to the maximum voltage that can be applied across the
capacitor.

> Can someone send me a HIGH resolution, CLOSEUP scan of the COMPONENT side of
> the FRONT  (nearest to the keyboard) of the Ohio Kache Systems MultiCache
> board?  I think Steven Buggie has one of these cards, could he do it for me?
> There is also one other CSA2 reader that has one of these boards, but I cannot
> remember his name  (??John??)

Sorry - can't help there (I've never even seen this card).

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand