On Tue, 20 Oct 2009 13:01:22 -0700, wrote:

On Fri, 25 Sep 2009 06:59:58 +1000, Franc Zabkar
wrote:

On Thu, 24 Sep 2009 11:32:39 -0700, put finger
to keyboard and composed:

The transistors are in a package equivalent to a Sanyo PCP
http://datasheet.digchip.com/413/413...-0-2SD2099.pdf The
transistors have identification that looks somethng like this:

DK
o_
QH

Sanyo PCP1201:
http://www.semiconductor-sanyo.com/ds_e/ENA1164.pdf
http://pdf.dzsc.net.cn/20090227/200902171141512888.pdf
http://www.semiconductor-sanyo.com/s...6&prod=PCP1201

- Franc Zabkar
Frank,

Well, another problem has raised it's ugly head, and I've finally
firmly established the source of these transistors. The Sanyo part
you tentatively identified was unavailable from my US sources. After
some research, I decided a dxt3150-13 would be an acc3eptable
substitute, so I ordered some. Since the original caps in the monitor
were Elite brand (a known 'bad' manufacturer), I ordered replacements
for them from the same distributor. Before placing the order, I
established the monitor would behave in the expected way with the
shorted transistors removed. I also tested the transformer to ensure
it was not defective.

With the shorted transistors installed, the screen would flash dimly
for a few seconds, then go blank. After they were removed, the screen
would come on for a few seconds, then blank. (This is the normal
result of the protection circuits shutting down the inverter because
of insuffficient output). When the replacements arrived, I soldered
in the new transistors and tested it. It worked perfectly for a few
minutes, so I shut it down and began to replace the questionable caps.

After recapping, the intermittent dim flashes returned!!! However,
neither the original nor the replacement transistors are shorted. It
is a puzzlement; I'll be using a scope to see if I can figure out the
problem.

In the meantime, I had received a Viewsonic VX910 monitor. The owner
indicated it was having difficulty turning on, but would eventually
start. Rather than try to verify this, I simply opened up the
monitor, and found three obviously bad caps. These were Capxon, also
notorious for premature failures. And while I was at it, I replaced a
fourth Capxon capacitor, in the inverter circuit. When I turned it
on, it gave the smae symptoms as the Sceptre monitor. And the
transistors were not shorted.

Researching the Viewsonic, I found it was sold in Germany as a
Belinea, and a complete service manual (including schematic and parts
list) was available for download. What's more, both the Sceptre and
Viewsonic used the same design for the inverter!! Browsing the parts
list, it turns out the transistor in question is a Rohm 2SC4672. DK
is the part identifier, Q indicates the gain range, and K appears to
be some sort of production or date code.

PlainBill
There is a tenedency to say that because two events (no display on two
monitors) occured after a pair of similar events (replacing the caps
on the power supply / inverter boards for the monitors), there must be
a common cause. Well, there was, but it was biological in nature, not
electronic. The scientific term would be 'incompetent technician'.

On the Sceptre monitor, reseating the connections for the CCFLs solved
the problem. It is currently undergoing a 'burn in' phase prior to
being reassembled.

On the Viewsonic monitor, testing the transistors showed that a pair
of them are shorted. And since there were none of the characteristic
probe marks on them, the logical conclusoin is that I INTENDED to test
them, but neglected to.

PlainBill