Electronics > Beginners

repairing crt tv, start with recapping

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2takt:
here is the big psu cap 330uf 385v rated, so this one is bad

2takt:
that sounds like my old sony always have to give him a little smack on the side xD
i will check the rest of the caps with my meter then i begin the reflowing.

so the isolation in the tvs psu is not enough for oscilloskop use?



and here is the resistors and the white dryed fluid. hoPe you can see it

Gyro:

--- Quote from: 2takt on August 29, 2019, 06:16:56 pm ---here is the big psu cap 330uf 385v rated, so this one is bad

--- End quote ---

Nope, that still looks acceptable for a 330uF non-SMPS high voltage capacitor.

2takt:
ok i found 1 and the display said good if <1000uf the cap was a 1000uf. so this should be good too?

update my esr meter just gave up on me. had serveral zerroing errors. now it show 0L when shorted great :)

Benta:
In all the CRT TVs I've repaired (and they were many), the primary fault mechanism was to 99% solder joint failures. Secondary component failures then followed as collateral damage.

The high voltage horizontal and vertical deflection circuit is the part of your main board that's most prone to failure due to high thermal and mechanical stress. Thermal, because it gets hot, and mechanical because the parts are heavy (compared to a resistor).

A simple reflow of the main board will not help. A manual resolder/reheat will also not help.

You'll need to remove the old PCB solder joints under the high voltage components (solder wick, rework station, whatever you have) and resolder them manually with Eutectic electronics resin solder (60/40 or close). Modern lead-free solder will not work on components this old.

Why? The old solder joints have one or two issues.
First, they're oxidized over the years and a simple reflow will not break the oxide.
Second, There's a production issue called "Tin Depletion". Tin has a higher affinity to copper than lead, so when several thousands of PCBs have been run through the wave soldering machine, the solder is no longer eutectic, but lead-heavy. Quality manufacturers monitor this, but it was an issue 50 years ago.

SAFETY ISSUES:
1: make certain that all large capacitors are discharged (easily done with a multimeter).
2: discharge the CRT. Connect a wire between chassis ground and an insulated screwdriver. Press the point of the screwdriver under the "suction cup" on the CRT.

Let us know how you get along. Cheers.

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