Entertainment Center: TVs, Stereos, VCRs and DVDs - Persistent Pioneer SDP6085K Convergence Problem
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Rick_Here
08-27-04, 11:50 PM
Anyone familiar with Pioneer big screens and up for a challenge?! I have been tinkering with a problem for several weeks and don't seem to be able to find the source. Symptoms are that the Green portion of the picture at both the top and bottom of the screen is bowed in significantly toward the center. Red and Blue are fine. Dusting off my old scope for the first time in five years or so, I found the Green amp in the STK4277 was clipping on the negative side, so I replaced it and now it amplifies like it should... except that this didn't solve the problem.
Comparing Red, Blue and Green outputs from the 4277, the Red and Blue are basically identical and both look good. The Green output has an additional modulation content at about 2.3 MHz that shouldn't be there! Checking the input, that same signal content is there also, so I also tried replacing the prior stage opamp for the "GV Out" amplifier (an M5228P). No change.
The PIN adjustments for both Wide and Normal screen modes do function properly going into the M5228P and you can see the change in the output of the 4277, but this additional modulation apparently keeps this from having any effect on the picture. I'm pretty sure this high frequency signal is the problem, but I have no clue where it's coming from.
One other note: the problem disappeared for about 30 minutes during one of my troubleshooting sessions, leading me to think maybe it was temperature related. But that happened only that one time out of maybe 20 times I've powered the set up.
I have photos of the set picture and scope photos of the 4277 outputs that I can e-mail if anyone would like to see what I'm talking about. Sure would like to get this thing working again if anyone has any ideas. Thanks!
Comparing Red, Blue and Green outputs from the 4277, the Red and Blue are basically identical and both look good. The Green output has an additional modulation content at about 2.3 MHz that shouldn't be there! Checking the input, that same signal content is there also, so I also tried replacing the prior stage opamp for the "GV Out" amplifier (an M5228P). No change.
The PIN adjustments for both Wide and Normal screen modes do function properly going into the M5228P and you can see the change in the output of the 4277, but this additional modulation apparently keeps this from having any effect on the picture. I'm pretty sure this high frequency signal is the problem, but I have no clue where it's coming from.
One other note: the problem disappeared for about 30 minutes during one of my troubleshooting sessions, leading me to think maybe it was temperature related. But that happened only that one time out of maybe 20 times I've powered the set up.
I have photos of the set picture and scope photos of the 4277 outputs that I can e-mail if anyone would like to see what I'm talking about. Sure would like to get this thing working again if anyone has any ideas. Thanks!
zigzag
08-28-04, 12:27 PM
Replace all 220 mfd capacitors on the convergence board.
:)
:)