Apple II Computer Info
pin 2 to pin 7
pin 3 to pin 6
You can use an Ohm meter to detect which one is open. (Example: the
correct reading from pin 2 to pin 7 would, probably, be less than an
Ohm.)
The 'catch' in all this is ... Why did the inductor burn out?!
Since the pin2-pin7 inductor connects to +5V on the pin7 side, it
appears that pin2 is, some how, shorted to ground.
Another possible candidate is the pin1-pin8 inductor. Pin8 connects
to +5V through a 470 Ohm resistor. If pin1 should be shorted to ground,
there _might_ be enough current to heat up and burn out the pin1-pin8
coil. However, this does not seem likely.
With the motherboard removed and KB disconnected, check Resistance
from pin1 to pin8, etc.. When you find the open (high R) inductor, check
R from the low-numbered side (1, 2, or 3) to Ground. (The silvery metal
shield near the ADB socket should be = Ground.)
If you discover a low R (like a few Ohms) to ground on the low
number side of the blown inductor, my guess is that it will be at pin2
and that the culprit is a shorted capacitor, BC91 and that your GS is a
ROM-03 (since no capacitor is shown on the ROM-01 schematic). If this is
the case, cut the trace to the capacitor and replace it with a compact
0.01 uF capacitor rated at 15V or better.
Another possible cause of shorting is a bent piece of shielding
near the ADB connector.
If you discover no short on the low-numbered pin of the blown
inductor, plug in your ADB cable without the KB and measure again. If
you, now, find a short, the indication is a messed up cable.
If there is, still, no short plug in the KB. A short now would
indicated a messed up connection at the KB socket.
If there is, still, no short, try the check while wiggling the
cable and plugs on both ends.
If you can find no short, my suggestion is that you remove the
bottom and back shields and throw them away-- they are a shorting
hazard.
After repairing the blown coil with a bit of coiled wire, put
everything together and see if your GS is fixed.
Rubywand
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Apple II Computer Technical Information : Apple II Family Hardware Info
ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 23 of 572
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