Transistor help

From: Dwight Elvey <elvey_at_hal.com>
Date: Thu Mar 18 16:13:24 1999

allisonp_at_world.std.com wrote:
> On Thu, 18 Mar 1999, Dwight Elvey wrote:
>
> > Hi All
> > I have been looking for the specs of a transistor
> > that burned out on my Cromemco board. It seems to
> > be obsolete. I tried the NTE suggested replacement
> > but that didn't seem to have enough gain to work
> > correctly. None of the books I have show it.
> > It is a MPS6560.
> >
> > I'm looking for max current, Vcbo and hfe.
> > Thanks
> > Dwight
>
> Which cromemco board??? Likely if the transistor doesn't ahve enough
> gain there is another circuit fault as the 6560 is pretty loose spec
> device.
>
> Allison
>

Hi Allison
 It is for a 8K Byte Saver. It is used for the flyback
driver for the high voltage supply. All of the other
transistors on the board are normal general purpose
types. The replacement transistor
that NTE had didn't seem to have enough gain. In order
for a flyback switcher to work, the edges have to be sharp.
I currently have a 2N4401 in there but it may have too much gain
or not be able to handle the higher reverse voltage on the
base lead caused by the feed back. The first one I tried
only lasted a few minutes. The next one I tried, I used a
larger base resistor and it seems to be holding but I'd
like to know what the intended gain and voltage range is.
The 2N4401 is not getting hot and I'm able to program parts
OK now, I'd just like to fix it correctly.
 One of the others said Mouser Electronics (800-346-6873)
carries them ( Thanks Arfon ).
 The transistor was blown trying to program a bad PROM. There
doesn't seem to be any other damage. The transformer seem
OK.
Dwight
Received on Thu Mar 18 1999 - 16:13:24 GMT