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

[Rubywand <rubywand@swbell.net>]

TWS writes ...

 ....
> 
> Thank you for the suggestions.  I see **NO** toasted components on the board.
> 
> PHYSICAL "defects" of the card:
> 
> 1) It appears that capacitors got MOVED/ removed.  I don't see why this would
> cause a short.  8 Caps on the board are PRESENT, but their connections have
> obviously been soldered on.  8 OTHER caps on the board are NOT present.  It is
> obvious that the connections have been soldered on.
> 
> 2) There has been a "jumper" wire soldered on to the board  (the connections
> look like they were soldered on at the same time the Capacitors were.)
> 
> I removed the jumper wire.........NO LUCK.  PS buzzzzes.
> 
> The GROUND/+5V connectors are at the BACK of the slot connector, correct?
> Those pins are nearest the back of the computer?
>

     Right. When the card is plugged in, the two pins closest to the
back of the computer are +5 and Gnd. One side (pin 25) is +5, the other
side (pin 26) is Gnd. 

 
> 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.
>

     It is normal to place a moderate size (10uF or larger) capacitor
near the main power input pins of a card. The + side should go to the +5
pin and the Gnd/- side should go to Gnd.

     If this capacitor has bombed, it could be shorted, which would
short +5 to Gnd.


 
> 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.
> 
> 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
> -

     Yes, these are capacitors-- probably, some sort of "dipped"
tantalum type. They are using one of the popular methods of coding:

106 ---> two significant digits of value (10) with a count of the number
of zeros (6) to express the value in pF-- pico Farads-- (also called uuF
or micro micro Farads).

104= 10 0000 pF or 100,000pF= .1uF (.1 micro Farads)
106= 10 000000 pF or 10,000,000pF= 10uF (10 micro Farads)

+25 ---> with this coding would indicate the rated voltage. Location of
"+" _may_ be used to indicate which lead is "+".

K ---> as a trailing letter or separate 'boxed' letter indicates 10%
value tolerance (J=5%, G=2%, F=1%, D=.5%, B=.25%, A=.1%)


     Many such capacitors will use a different marking: the value will
be shown directly as, say, "10uF" and Voltage rating may be shown as
"35V", etc..


> 
> Questions::::::::::::::::
> 
> Which pins on the board are +5v and Ground?  Nearest the BACK or FRONT of the
> computer?

     Pin25= +5V and Pin26= Gnd--- nearest back of the computer.


> 
> 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??)
> 
> I'd like to check if the board is supposed to have parts C-21==C-24,
> C-17==C-20.   Thats what I'd like the scan for.  Also, I'd like a scan of the
> BACK  (non component side) of the board, near the BACK  (nearest to back of
> computer).
> 
> This is where the jumper is located, and I am curious if the board is SUPPOSED
> to have this jumper.
>

 ....

     It is common to have jumpers near the power input pins as a way to
route +5 or Gnd to traces which may be on the other side of the board. A
jumper from +5V to Gnd would be incorrect-- it would short +5 to Gnd.



-------

TWS wrote:
> 
> I located another "defect" on the card.
> 
> An IC, labeled
> 
> 74ls14n
> Skk8522  AF
> 
> Has had a pin removed!  (I don't know how the heck it happened.  The chip is
> soldered directly to the  board.  Maybe the card was built this way)
> 
> Does anyone know what this chip does?
> 
>              | | | | | | |           <----pins got away from the chip
>              ____________                 in my ASCII drawing
>              |           |
> "dimple --->  }          |
> in the       |___________|
> chip         | | | | | | |
>                ^
>                |
>              this is the BROKEN pin.  Pin #2 from the left.


     The 74LS14 is a hex Schmidt trigger inverter IC-- i.e. six separate
inverters, each having a Schmidt trigger input. The pinout is similar to
the more common 74LS04 hex inverter IC.

     It is difficult to know whether the broken pin indicates damage or
if it was removed on purpose due to some design revision which needed to
remove a signal from the lines going to pin 2-- i.e. this might be
easier than cutting traces going to pin 2. (Pin 1 is an inverter input,
pin 2 is that inverter's output. There are five more inverters -- 3 to
4, 5 to 6, etc..)

     In any case, the missing pin would not cause a short (unless it is
somehow stuck under the socket and across the +5 and Gnd power rail).

     If you eliminate the shorting problem and discover that the card
works okay, fine. If the card messes up, you could try swapping in a
74LS14 with all of its pins. (Swapping in a 74LS04 or 7404 or 74S04 is a
'try'-- for sure, many experimenters will not have a 74LS14 in their
parts bins. If the card, then, seems to work fairly well but, still,
sometimes, messes up, the indication would be that you need the Schmidt
inputs of the 74LS14.) 


     Your description of the board indicates that someone has already
been pulling caps and substituting new caps. If many of the caps spread
around the board are "106" (10uF) value, it appears that rather large
values were substituted for the original caps.

     It is common to spread caps around a circuit to supply by-passing
of noise glitches on the power rails going to IC's-- e.g. there will be
a cap near an IC which connects to +5 and Gnd. A typical value is
something in the range .05uF to about .5uF. A major consideration is
that these caps have short leads and simple construction to minimize
inductance effects which tend to defeat bypassing at high frequencies.
The particular 10uF dipped caps used may be okay for glitch by-passing
on this board-- really, I don't know-- however, regular 10uF/25V
aluminum electrolytic caps would be pretty useless.

     Even so, a few over-sized caps are not going to cause a dead short
unless one or more of them is actually shorted. (Of course, if the
jumper you mention is going between +5 and Gnd, _that_ is sure to be a
short.)

     Before you snip or desolder any caps, it would be a good idea to
see if pulling any socketed IC gets rid of the shorting condition at the
power input pins (25 and 26). Use an Ohm meter for this.  (In general,
it is not a good idea to plug in a card from which you have pulled an IC
in order to check for shorts.)

Note: The reason for suggesting that the Ohm meter leads connect + to
card Gnd and - to Card +5 is that most Ohm meters seem to pass current
through the tested circuit with the - lead being the positive side of
the source (a battery) inside the meter.

     Good luck with the checks and with finding a schematic for the
board.



Rubywand