YD wrote:
Late at night, by candle light, Eeyore
penned this immortal opus:



"John E." wrote:


Ah, another ITT diode on the board starts with "ZY" (where "Z" could be
mistaken for a "4" on the charred carcass). So I looked up ZY47 and get a
4.7v power zener diode, 2W.

http://www.allcomponents.ru/diotec/zy47.htm

Also, according to a National data sheet I found, a 1N4147 (a.k.a. 1N914A) is
glass, and way too lightweight physically compared to my charred sample.
Wrong turn, I think.

So it looks like ZY47?

BZY47-C47?

2 watt zener 47V ? The number after the C is the voltage. 4.7 volts would be
BZY47-C4V7 btw.

Graham


Spot-on I think. It'll normally have 42 V across it, not enough to
conduct. When de-energizing there'll be a spike wich it clamps at 47
V. Dunno why the 1 uF cap.

- YD.

So, if all the conduction it should get is from the odd spike, how come
it got the San Quentin hairdo? It takes rather more than static to fry
chips.

My thoughts would be that the supply rails are screwed. If the unit has
a positive and negative rail, it may be that the ground return to the
psu has problems and thus more than the 42v is appearing across the
zener, as the ground point has shifted towards the negative rail.


--
Sue