[TechAssist] Re: Second Postin: Pioneer VSX 425 Dolby surround w/video.
- From: "Rob Svilpa" <robesv@xxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Tue, 6 May 2003 13:03:17 -0700
I had a problem with a cracked circuit board at the power amp output
circuitry after shipping my Yamaha A/V surround unit from back east.
Checked all the components but didn't find anything blown. The internal
circuit breaker would trip though as soon as I kicked on the surround
feature which powered up the center channel amp. Turned out that a
cracked board on the center channel output was causing overload on the
power amp - causing extreme distortion and massive phase cancellation on
the output for the 5-10 seconds it took for the breaker to trip.
I had to epoxy that section of the board and jumper the tracings by hand
to get the thing working again. It was dropped in its shipping box and
the output posts had been pushed in slightly causing the board to crack
inside the case. I was relieved that it was a simple circuit to fix
since if it was more than 1 layer of tracings I would have been S.O.L.
I don't know if that helps, but if there is some phase cancellation
between the rear or center channel and the mains that would cause the
distortion to appear only when the surround circuitry is enabled...
Rob Svilpa
SDET
Microsoft Corporation
Redmond, WA
-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of Tiberius Kraemer
Sent: Tuesday, May 06, 2003 12:38 PM
To: techassist@xxxxxxxxxxxxx
Pioneer VSX 425 Dolby surround w/video.
This one has me stumped.
Right Front channel was blown, had no problem repairing it.
Tested the unit overnight, at 80% capacity into an 8 ohm load, it is
solid
as a rock.
This morning I switched over to surround sound. The distortion is
unbearable.
Clips like crazy at about 30 percent of capacity. Ok, I figured there
must
be something wrong with the decoder circuitry. Used old Green-eyes
(Oscilloscope) to check the input to the main amps. Signals are clean.
Jumpered, using coupling capacitors at the output of the pre-amp, to
the
bench amplifier. There is no distortion either in normal stereo or
Surround
mode audible or visible on the scope at any volume setting.
Must be the Power supply! Wrong! Holds as steady as a rock.
Not having the manual for this unit, I can not figure out why the unit's
main amps distort (clip) only in surround mode.
Your input would be most welcome.
Ty
Tiberius Kraemer
Blue Star Electronics
3312 Silverton Rd. NE
Salem, Oregon, 97303-2753
Phone: 503 391 1491
ty1K@xxxxxxxxx
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