Hi all,
I have a PVM-20M4A with an issue with the pincushion where the horizontal section is stretched well beyond the screen and horizontal geometry adjustments make no difference. Vertical adjustments work correctly. I apologise that I don't have a cross hatch pattern to show, I annoyingly forgot to snap a picture, but I do have one of the service menu showing the issue somewhat. https://imgur.com/a/YCZkRms
I believe this is the same issue as detailed in the two following links:
viewtopic.php?f=6&t=69677&fbclid=IwAR3c ... 37pMVocYk8
https://www.reddit.com/r/crtgaming/comm ... ff_screen/
A bit of necessary context, I bought this PVM in a non-working state, without any idea what was broken. It had a blown HOT, as well as two blown ICs on the PSU. I have since replaced all the damaged ICs and have done a recap on the PSU, as well as most of the deflection area (what's recommended in the Savon Pat kit). I need to state that I am very new to electronics repair and this is my first time working on a CRT, but I have some soldering/disordering experience. I'm stoked to even get it to fire up, and I'm determined to fix it. I do not however have the confidence to probe this thing while its running.
Any advice would be greatly appreciated.
Sony PVM-20M4A Pincushion distortion issue
Re: Sony PVM-20M4A Pincushion distortion issue
Hi Team,
So long story short, I managed to fix my issue.
After staring at the A board for hours, I noticed that in my case, the positive leg of C579 had a lifted pad. Initially, I didn't think too much of this because it was still in continuity with the next part over, R1508. However once I checked the schematics, I realized that this meant that the via wasn't connecting on the other side of the board, and it was directly connected to the Vcc of IC509. IC 509 being the pinamp control chip.
I checked for continuity between the positive leg of C579 and pin 8 of the IC (very difficult as this was underneath the capacitor, used a jumper wire attached to my probes) and confirmed no continuity. So I wrapped a resistor leg around the joint and added a bit more solder to make a good joint, confirmed continuity and when I fired it up, it was fixed!
Here are some pics: https://imgur.com/a/9A5G1eU
Now from my understanding, this circuit can fail at a few different points, this just happened to be where mine failed. Its best to start at the diodes and work your way from there. I'd start by looking for any short paths to ground across D506, D502, D512 and C525, as well as C514 and C2510. You can do this by checking the resistance across the components using the heatsink of Q501 like this: from the red circle to the four yellow circles, as well as across A and B https://imgur.com/5wdi0Wq. You can also do this across the legs of C514 and C2510, resistance should be in the kiloohms or higher (mine was about 53kohms). Thank you to @MKL for all their help and guidance with this issue.
Q503 can also be tested with a multimeter in diode mode once removed from the board. With the red probe on the left leg and the black probe on the middle and then the right leg. You should notice around 0.5-0.7v, with the latter combination being slightly higher. All other combinations should show O/L.
I'd recommend one of the cheap component testers from Aliexpress if you're looking to desolder and individually test components. They're worth every penny.
So long story short, I managed to fix my issue.
After staring at the A board for hours, I noticed that in my case, the positive leg of C579 had a lifted pad. Initially, I didn't think too much of this because it was still in continuity with the next part over, R1508. However once I checked the schematics, I realized that this meant that the via wasn't connecting on the other side of the board, and it was directly connected to the Vcc of IC509. IC 509 being the pinamp control chip.
I checked for continuity between the positive leg of C579 and pin 8 of the IC (very difficult as this was underneath the capacitor, used a jumper wire attached to my probes) and confirmed no continuity. So I wrapped a resistor leg around the joint and added a bit more solder to make a good joint, confirmed continuity and when I fired it up, it was fixed!
Here are some pics: https://imgur.com/a/9A5G1eU
Now from my understanding, this circuit can fail at a few different points, this just happened to be where mine failed. Its best to start at the diodes and work your way from there. I'd start by looking for any short paths to ground across D506, D502, D512 and C525, as well as C514 and C2510. You can do this by checking the resistance across the components using the heatsink of Q501 like this: from the red circle to the four yellow circles, as well as across A and B https://imgur.com/5wdi0Wq. You can also do this across the legs of C514 and C2510, resistance should be in the kiloohms or higher (mine was about 53kohms). Thank you to @MKL for all their help and guidance with this issue.
Q503 can also be tested with a multimeter in diode mode once removed from the board. With the red probe on the left leg and the black probe on the middle and then the right leg. You should notice around 0.5-0.7v, with the latter combination being slightly higher. All other combinations should show O/L.
I'd recommend one of the cheap component testers from Aliexpress if you're looking to desolder and individually test components. They're worth every penny.
Re: Sony PVM-20M4A Pincushion distortion issue
Cool, glad you fixed it. Thanks for sharing!