On Sat, 09 Apr 2005 03:38:08 GMT, "James Sweet"
put finger to keyboard and composed:


"z" wrote in message
om...
My SO accidentally used reverse polarity for the 6v dc power supply input
to the SuperScope PSD 230 portable CD player she just got secondhand.
She had not tried it before. Now it does not play with the power supply
only (tip positive, which I think is correct according to the diagram
on the outside of the box). However, it seems to play fine with
batteries.

Does reversing the polarity of a 6v dc power supply to an electronic
device
ordinarily fry the innards? Or is there usually some kind of protective
circuit that prevents this mistake from having serious consequences?

TIA...



If it still works on batteries then you got very lucky and there's probably
a protection diode, look for a burned trace or micro fuse near the input
jack. Usually reverse polarity will fry the device instantly, not sure why
they don't all have a diode.

A friend in the industry calls this a "dickhead diode". On quite a few
occasions I've added such diodes to protect myself from bounced jobs.
For some low power devices with a high enough supply margin you can
safely add a diode in series with the supply.


- Franc Zabkar
--
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