Electronics > Beginners
repairing crt tv, start with recapping
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Ysjoelfir:
The big one looks actually ok, the small one - not so. There is some corosion on the pins, so I would definitely exchange that one. The bigger one.... it depends. If you can afford it and find a suitable replacement, replace it.
Depending on the city you live in I could look in my cap stock pile if there is a fitting replacement waiting.
Benta:
The big one's OK, the small one is leaking, which can be seen on the PCB.
2takt:
the big one also had a round(leaking) mark on the pcb.

i life in germany.

i couldnt find any detailed information(again) about this two caps. the thing i found was:
https://www.datasheets360.com/part/detail/tvx1h221m/381254941137251487/

how do i find out what caps i need for replacement. so i already know they are low esr, what else is important besides the uF and V rating


i did notice when the tv is turned on there is a really small flicker on screen(noticeable on letters) but is gone after 10minutes. is this a normal behavior when cold?

the image is a little bit curved on the sides, has this something to do with my repairing? i have the service manual so i can programm the picture to be square again. but have to check the "system voltage" first. it should be 148V, can you tell me where i have to measure?
SparkyFX:

--- Quote from: 2takt on September 12, 2019, 07:44:18 pm ---i life in germany.
--- End quote ---
We too... check the country flags. Which city/area?


--- Quote ---one last question i also ordered this cheap oscilloscop dso 138. the service manual says:
the chassis is isolated from line voltage. the isolation point is in the line section.
can i measure the chassis without a isolating transformer?
--- End quote ---
The BNC ground is usually connected to protective earth, therefore it is not isolated in the sense of running the device-under-test with an isolation transformer. In most cases, all BNC sockets on the front panel share the same ground, so whatever you touch with the probe ground is live on those BNC sockets -> horribly unsafe to work with, without further provisions.


--- Quote ---how do i find out what caps i need for replacement. so i already know they are low esr, what else is important besides the uF and V rating
--- End quote ---
Capacity, voltage rating, temperature rating, the footprint of the part, obviously. ESR is usually somewhat defined by type of capacitor.


--- Quote ---the image is a little bit curved on the sides, has this something to do with my repairing? i have the service manual so i can programm the picture to be square again.
--- End quote ---
Even if the pillow setting can be done in software, first sort out the line transformer issue. These deflection grids are probably not working as intended when hit by the beam (lines that are not on the screen probably end in them).

Replacing the leaked capacitors is probably a move in the right direction.
Gyro:

--- Quote from: 2takt on September 12, 2019, 07:44:18 pm ---the big one also had a round(leaking) mark on the pcb.

--- End quote ---

Leakage marks... or just residue from board cleaning / normal environmental contamination? Hard to say but I think it is the latter - I can't see any sign of leakage around the terminal pins or bottom rubber, just marking on the end of the plastic sleeve.

It's worth at least thinking about replacing some caps after you've gone to the trouble of removing them but consider cost also. The caps around when that TV was built wouldn't have been the same as the ultra-low ESR ones used in compact, high switching frequency, SMPSs these days.

The factors determining capacitor replacements are capacitance value, voltage, ripple current (which effectively covers ESR too in these caps), temperature spec, and physical size / pin spacing. Remember that this is consumer equipment, the originals wouldn't have been exotic. With modern caps, you sometimes need to select a higher voltage part - simply to make the physical size big enough.

It's easy to 'see' picture defects in CRT TVs these days when you're used to modern digital LCD TVs. A bit of flicker on an interlaced screen is normal, as is a bit of curvature (which can probably be adjusted out if it really bothers you), I'd keep adjustments to a minimum.

The service manual ought to be specific on the voltage measurement points, often also marked on the PCB (with care!).
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