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Sony PVM-2130QM - Color RED bleeds and is blurry.
arcadeswede:
Hi!
I'm troubleshooting a Sony PVM-2130QM and the RED color has some bleeding or isn't in focus compared to the other colors. See image:
I've recapped the neck board (C) and PSU board (D). I've tried adjusting the RED Cut Off but that didn't change it. I've reflowed all solder joints on the neck board. Everything looks good. I've measured some test points and they're all within specs.
If you look at the BLUE and GREEN colors, they show good focus and colors. I'm thinking there's a bad ceramic cap or maybe a transistor that's the culprit on the RED channel?
Do you guys have any ideas?
Here's the service manual: https://ia801607.us.archive.org/28/items/sony_PVM-2130QM_Service_Manual/PVM-2130QM_Service_Manual.pdf
buttersoft:
Alright, that's a really ---steaming pile of meadow muffin--- photograph of what i think might be the problem. Can you bring up a test grid, or something with a big red-to-not-red transition? Would it look like the photo below?
Either way, with the power off, check resistor R702 on the neckboard and then probably R703, R704 and R706 just in case. You can replace each of those with a with a metal-film 2W resistor of like value if there's any problems. R702 can be checked in place once the nearby C-3 connector is removed. TBH it might meter fine, but that doesn't mean it isn't the problem. The solid-carbon used in that spot is a known issue on similar models, and i'd recommend replacing it regardless. Just remember that the caps on the neckboard of these might hold charge, i think it is.
Let us know how you get on and we'll go from there.
Zebidee:
Part of the problem with those solid carbon resistors is that they degrade over time a bit like electrolytic caps, and can take a long time to fail completely (vs metal film resistors that usually just fail short), making it hard to diagnose the problem.
If checking/changing those neckboard resistors doesn't help, try swapping colour drive transistors around - see if the same problem transfers to another colour.
arcadeswede:
--- Quote from: buttersoft on August 06, 2020, 07:39:58 pm ---Either way, with the power off, check resistor R702 on the neckboard and then probably R703, R704 and R706
--- End quote ---
Alright, here's the values:
702 = 691K (680K)
703 = 96.5K (100K)
704 = 524.7K (470K)
706 = 107.4K (100K)
Resistor 704 seems to be acting up. The other resistors looks like they're within specs. It was even desoldered and measured alone.
--- Quote from: Zebidee on August 07, 2020, 12:41:48 am ---If checking/changing those neckboard resistors doesn't help, try swapping colour drive transistors around - see if the same problem transfers to another colour.
--- End quote ---
Are we talking about Q701, Q704 and Q708?
buttersoft:
Do both the "screen" control RV701 and the sub-brightness control RV706 on the neckboard work normally, out of interest?
No guarantees, but TBH i'd replace R704 with a 2W metal film and see what gives. (If you have to wait ages to get parts, then order all the solid carbon resistor values on the neckboard and just replace them one by one starting with R704). Zeb and I have both seen this problem or a very similar one on the PVM-2730, and it seems to be caused by those 470K solid carbons...
Or really by the fact the grid voltages are too low, and pushing the bias voltage up into the cutoff zone of the red drive, i think. Which is not a transistor problem as such. Technically the drive transistors are Q702, Q705 and Q709. But this set has four transistors for each colour on the neckboard. You can try swapping them one by one if you need to. I'd look at other options first.