"Chuck" wrote in message
...
On Mon, 24 Jul 2006 17:26:42 -0400, "Michael" noreply@nospam wrote:

Shouldn't the STR3035 in this set maintain the 135V B+ steady?

This 1986, 27 inch TV (chassis SCC552P-A) came in with an open 1.6 A fuse,
defective FTB (1-439-372-11), HOT (2SD1497) and IC601 (STR3035 135V
regulator) amongst other things. I replaced the components as well as
several high ESR electrolytics and a resistor (in the horizontal centering
network). All the joints in the horiz. drive cct, as well as several in
other areas, were cleaned and resoldered. The horiz. deflection winding
rings 8 on my DSE FBT tester. Waveforms in the horiz. drive area and at
the
HOT collector appear to be normal. Although the HOT heat sink gets quite
warm, it stays within the measured temp. range I've seen on other Sonys.
The set works, and especially for a 20 year old, has a very good picture.
So what's the problem? The 135V B+ output of IC601 is not well regulated.
It varies depending on the AC line input.

When powered up at 115V AC in, there's about 157V at the input of the
regulator (pin 1) and about 131V at the output (pin 4). The 157V input
has
about 6V ripple. Pin 2 has a (forward-biased) diode to ground --there's
about 0.6V at pin 2. Pin 3 is connected to a network of several resistor
and two caps. All were checked individually and found to be good. I find
about 133 V at pin 3. The regulator is bypassed (pin 1 to pin 4) by a 120
Ohm 20W resistor -- it's good. The current through the 1.6 A fuse that
feeds the regulator is around 500 ma.

I don't have the schematic for this exact model but I do have several
others; for example, the Sony SCC552U-A chassis that has the same basic
STR3035 regulator layout. All the measurements conform to that indicated
in
the SCC552U-A schematic (SAMS).

I haven't located a data sheet for the STR3035, but based on my experience
with similar regulators, I would expect the 135V output to remain solid.
I
tried a second new IC as well as changed the diode at pin 2, to no avail.

At this stage I guess I'm looking for confirmation of the measurements
around the regulator (based on the proper schematic), and suggestions for
(or experience with) this symptom.

(Please reply to group.)

Michael C.E.T.



As long as the picture doesn't pull in from the sides during bright
scenes, I wouldn't worry about it. As a warranty servicer of this
model for many years, I can say that the regulation circuit wasn't one
of the best. Chuck

Ditto that. These were not the tightest supplies to start with.

Leonard


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