Electronics > Repair
Pincushion Issue on Sony CRT Monitor
FIXITNOW2003:
Long time since i have seen one off these .only have these notes
CPD1604S that displays its image as trapezoid a shape. Any adjustment I make only lasts until power off and shifts the narrow part from top to bottom check all the SMD caps for leaking or high ESR Also check all the SMD electrolytics for bad ESR, but don't stop there. These caps will sometimes leak fluid that can eat traces and vias underneath the caps, chances are there are several bad ones that need replacing. Esp. check C328 and C334, also IC303 = TEA2031A. Clean the board well of any leaked electrolyte, repair any damaged PC traces, and run wires through any damaged through-hole connectors underneath these caps. Readjust RV309.
CPD-1604S no picture, unit makes humming noise. Horizontal output ok. Try checking/replacing capacitor C911 = 10 uF, in the power supply.
CPD-1604S Pincushioning & Vertical Collapse after being on a while Reflow Main & CRT board.
vol.2:
--- Quote from: FIXITNOW2003 on October 10, 2024, 06:36:48 am ---Long time since i have seen one off these .only have these notes
CPD1604S that displays its image as trapezoid a shape. Any adjustment I make only lasts until power off and shifts the narrow part from top to bottom check all the SMD caps for leaking or high ESR Also check all the SMD electrolytics for bad ESR, but don't stop there. These caps will sometimes leak fluid that can eat traces and vias underneath the caps, chances are there are several bad ones that need replacing. Esp. check C328 and C334, also IC303 = TEA2031A. Clean the board well of any leaked electrolyte, repair any damaged PC traces, and run wires through any damaged through-hole connectors underneath these caps. Readjust RV309.
CPD-1604S no picture, unit makes humming noise. Horizontal output ok. Try checking/replacing capacitor C911 = 10 uF, in the power supply.
CPD-1604S Pincushioning & Vertical Collapse after being on a while Reflow Main & CRT board.
--- End quote ---
Hi, thanks for your comment.
I am working on the DA PCB now for electrolyte washing. I replaced all the electrolytics on that board when I first got it, but I think I missed some surface mount components that had electrolyte trapped underneath them. This board is filled with SMD transistors and such and is taking a long time to repair now.
When I'm done, I'll see if that is the fix, most probably is.
Thanks @suntime, I already tried to replace the TEA2031A and that made no difference. I've gone back to more PCB treatment. It's a long slog.
bostonman:
It's been many years since I worked on CRT monitors, but usually such problems were electrolytics.
Try a hair dryer (or heat gun) and see if the problem gets better.
vol.2:
--- Quote from: bostonman on October 10, 2024, 05:48:46 pm ---It's been many years since I worked on CRT monitors, but usually such problems were electrolytics.
Try a hair dryer (or heat gun) and see if the problem gets better.
--- End quote ---
Unfortunately, I ended up having to remove a large number of surface mount components to clean underneath of them and inspect things for damage. I found a couple of possible causes for the issue including a cracked resistor (that was still reading the correct value, but might have been experiencing issues under load), and a more heavily damaged area of the board that two transistors with corroded legs which kind of crumbled off when I removed them; they were still in circuit and voltages were mostly correct when I pulled them out, but they were clearly corroded on the inside somewhat and therefore could have been creating some weird effects.
The issue with this repair is that it isn't a "smoking gun" kind of situation where I can find a single bad part and match it to the symptom. Because the circuit is "mostly" working, it's just one specific area that is having issues, and the issues are related to current and not voltage. The only bad waveform I can find is Pin 7 on IC303, which suggests that the Sawtooth on Pin 1 is current limited, and indeed there is a slight amplitude issue on the waveform. It's not enough for me to have thought anything of it, but I had someone point out that it's a crucial spot to the effect of the circuit. If there is enough parasitics in the circuit leading up to Pin 1, the current balance will be off and the Pincushion controls will not function and viola.
The assessment was that there is 1) enough residual electrolyte on the surface of the PCB to make it conductive and create effects between the pins of transistors in the Pincushion circuit and/or 2) enough components have a small amount of damage from the electrolyte to create extra resistance in the circuit and current limit Pin 1.
I removed all the components from the effected areas including the areas involved in the Pincushion stuff, washed the board with warm water for a few hours and dried it thoroughly including a second wash with IPA to drive moisture out of nooks and a heat gun.
I've got replacement transistors and a bunch of high accuracy resistors to replace almost everything, so I'll just do that and cross my fingers.
If I do that and the fault is the same, at least I'll know what it isn't. I suppose if the fault is the same, it will probably turn out to be a broken trace I missed somewhere, or a broken via given that it's a double sided board.
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