J
John Miles
Guest
Pioneer has recently released a service bulletin on their Pro-x30HD line
of RPTV sets that purports to address a widespread problem with colored
(R/G/B) streaks that intermittently appear during warmup, typically
during the first hour or so of operation. The impression I'm getting at
www.hometheaterspot.com's Pioneer forum
(http://www.hometheaterspot.com/htsthreads/postlist.php?
Cat=&Board=UBB20) is that virtually all Pro-x30HD sets will eventually
exhibit this symptom. My 12-month-old Pro-630HD has just started acting
up, so I've called Pioneer to get in line for the "fix."
There has recently been some specific discussion of the service bulletin
on the HTS board. Evidently, Pioneer has been attempting to shotgun
this problem to death for some time now, disgruntling a few customers in
the process, but they claim to have solved the problem once and for all
at this point. The bulletin turns out to address a part of the video-
driver subsystem that I don't understand. Basically, I don't see how
their recommended fix works, and I was wondering if someone with RPTV
service experience could clue me in. (I'm more-or-less literate in an
EE sense but don't know much about RPTV internals.)
In these particular sets, the screen grids on each of the three CRTs
appear to be tied together and connected to the focus terminal on the
FBT, with individual spark gaps on each driver board that bleed off any
voltage surges to ground. Except the cold ends of the spark gaps aren't
grounded directly: they're returned to ground via a parallel combination
of a 47-ohm resistor and a standard silicon diode, D5110/D5160/D5210,
with the anode tied to the main chassis ground and the cathode tied to
the cold end of the spark gap.
The service bulletin (CRTX30-INS) calls for an additional diode of the
same type (basically a 1N4004 as far as I can tell) to be placed in
series with the existing D5110/D5160/D5210 diode at each board.
The schematic in my service manual shows the cold end of the spark gap
(which is now supposed to be *two* diode drops above chassis ground) to
be connected to the "CRT STAND", all of the unused ("GND") pins on the
CRT socket, and not much else. (The protective spark gap on the cathode
pin is also tied to the floating ground, for what it's worth.)
Can anyone tell me why they've elevated the CRT ground and spark-gap
returns above chassis ground with this diode/resistor combination? I
don't see anything connected to the elevated ground that might be
affected by adding another diode, which makes me think my service manual
isn't telling me the whole story.
The impression I get is that there's a module called "FOCUS VR1" that
sits between what Pioneer calls the "deflection service assembly" (with
the flyback) and the screen connections on the CRT driver boards. The
schematic for the FOCUS VR1 module does not appear anywhere in the
manual as far as I can see. Maybe there's some circuitry associated
with this assembly that inhibits "streaking" by changing the TV's
operating parameters in response to spark-gap activity, but that needs a
little more voltage to trigger?
Would appreciate any advice.
-- jm
------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------
of RPTV sets that purports to address a widespread problem with colored
(R/G/B) streaks that intermittently appear during warmup, typically
during the first hour or so of operation. The impression I'm getting at
www.hometheaterspot.com's Pioneer forum
(http://www.hometheaterspot.com/htsthreads/postlist.php?
Cat=&Board=UBB20) is that virtually all Pro-x30HD sets will eventually
exhibit this symptom. My 12-month-old Pro-630HD has just started acting
up, so I've called Pioneer to get in line for the "fix."
There has recently been some specific discussion of the service bulletin
on the HTS board. Evidently, Pioneer has been attempting to shotgun
this problem to death for some time now, disgruntling a few customers in
the process, but they claim to have solved the problem once and for all
at this point. The bulletin turns out to address a part of the video-
driver subsystem that I don't understand. Basically, I don't see how
their recommended fix works, and I was wondering if someone with RPTV
service experience could clue me in. (I'm more-or-less literate in an
EE sense but don't know much about RPTV internals.)
In these particular sets, the screen grids on each of the three CRTs
appear to be tied together and connected to the focus terminal on the
FBT, with individual spark gaps on each driver board that bleed off any
voltage surges to ground. Except the cold ends of the spark gaps aren't
grounded directly: they're returned to ground via a parallel combination
of a 47-ohm resistor and a standard silicon diode, D5110/D5160/D5210,
with the anode tied to the main chassis ground and the cathode tied to
the cold end of the spark gap.
The service bulletin (CRTX30-INS) calls for an additional diode of the
same type (basically a 1N4004 as far as I can tell) to be placed in
series with the existing D5110/D5160/D5210 diode at each board.
The schematic in my service manual shows the cold end of the spark gap
(which is now supposed to be *two* diode drops above chassis ground) to
be connected to the "CRT STAND", all of the unused ("GND") pins on the
CRT socket, and not much else. (The protective spark gap on the cathode
pin is also tied to the floating ground, for what it's worth.)
Can anyone tell me why they've elevated the CRT ground and spark-gap
returns above chassis ground with this diode/resistor combination? I
don't see anything connected to the elevated ground that might be
affected by adding another diode, which makes me think my service manual
isn't telling me the whole story.
The impression I get is that there's a module called "FOCUS VR1" that
sits between what Pioneer calls the "deflection service assembly" (with
the flyback) and the screen connections on the CRT driver boards. The
schematic for the FOCUS VR1 module does not appear anywhere in the
manual as far as I can see. Maybe there's some circuitry associated
with this assembly that inhibits "streaking" by changing the TV's
operating parameters in response to spark-gap activity, but that needs a
little more voltage to trigger?
Would appreciate any advice.
-- jm
------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------