Caps that appear fine still

[lnx64]

So I have an old television from around the early 80's. It's an old Samsung with Samwah and Samsung branded caps. The caps appear to be running completely fine still, even after many years of service. The picture is strong, bright, and vibrant. Only oddity is the speaker has a slight buzz to the vertical refresh rate (60Hz on NTSC sources and 50Hz on PAL sources). This to me inclines one of the caps may be going out of tolerance, but everything looks great inside, no buldges, nothing leaking, and when i run an ESR test on each cap, they actually pass.

If they still pass an ESR test and the picture still looks good, case of don't fix if it ain't broke, or replace anyway? Thing is the buzz on the speaker may have just been a design fluke since the audio isolation transformer on it is directly under the CRT's yoke.

Anyway, literally the only repair this TV ever needed was a new flyback transformer which I installed myself (since it was far cheaper for me to do it and I know how to handle them without getting hurt).

[mockingbird]

Re: Caps that appear fine still

How do you know you're getting reliable ESR measurements when testing the caps in circuit?

[lnx64]

Re: Caps that appear fine still

How do you know you're getting reliable ESR measurements when testing the caps in circuit?

I never measure in circuit, too many variables can affect the outcome. I removed them from circuit.

This was tested though about a year and a half ago when I got the TV.

[ben7]

Re: Caps that appear fine still

I still am betting that the cap(s) might be the problem.

Besides, what esr ratings/charts are you using? Usually these are just generalized values, so a low esr cap which reads a bit higher in esr (like that of a non low-esr cap of the same capacitance/voltage) would be 'fine' - according to the chart, that is!

[mockingbird]

Re: Caps that appear fine still

ben7 makes a good point. How do you qualify "passes an ESR test"... There are probably no series markings on these ancient caps. I've watched some arcade refurb videos, and TV re-caps are almost always done on cabinets from the 80s. If you do re-cap, don't buy a "kit" put together by someone for your specific model. These kits often contain substandard parts. Check if the caps have a series printed on them, and replace the large primary caps as well.

[c_hegge]

Re: Caps that appear fine still

I'd recap it anyway. Why, you ask? Because the original caps have no vent stamps and would be much more fun to throw in a fire

[lexwalker]

Re: Caps that appear fine still

So I have an old television from around the early 80's. It's an old Samsung with Samwah and Samsung branded caps. The caps appear to be running completely fine still, even after many years of service. The picture is strong, bright, and vibrant. Only oddity is the speaker has a slight buzz to the vertical refresh rate (60Hz on NTSC sources and 50Hz on PAL sources). This to me inclines one of the caps may be going out of tolerance, but everything looks great inside, no buldges, nothing leaking, and when i run an ESR test on each cap, they actually pass.

Its possible that the buzz problem comes from the video signal detect circuit. On some TVs, the audio will only be enabled when there is a video signal detected at the input. (e.g. possibly resistor-capacitor charging/discharging method similar to switch debouncing). Also could be shielding issues. Other than that check the decoupling capacitor at the audio amplifier side.

[lnx64]

Re: Caps that appear fine still

This one doesn't auto mute, it's a rather crude and simple TV.. It has VHF and UHF knobs on it..

But, the dc coupling capacitor, this would be interesting to look into.



That's the schematic to the chassis on this TV.. The last pages are for the digital tuning some models of the TV had, but mine doesn't have that so only the main board's schematics are true.