Electrolytic Capacitors With Higher Stamped Value

[Michael/5of9]

A very good day to you all on Electronics Point Forum

I have just finished testing all of my Blue Electrolytic Capacitors on a Philips cassette deck and I have found some with extraordinary high capacitance readings; four 100μf 4v and 10v redial caps gave 158.4μf, 247.4μf, 155.4μf and 164μf; these are much higher readings than the stamped value.

I need advice on this whether to replace them; they most probably were like this when it was built and commissioned, so with this in mind it would be best to leave them fitted?

I do have a 47μf 10v redial that gives/reads 45.4μf; I intend to replace this with a Vishay 136 RVI 47μf 63volt, this is the nearest to match?

 

[duke37]

If the capacitor is leaking, then it will take longer to charge and appear like a larger capacitance.
Measure leakage at rated voltage.

 

[Michael/5of9]

If the capacitor is leaking, then it will take longer to charge and appear like a larger capacitance.
Measure leakage at rated voltage.

With simple test equipment how would I obtain this answer?

 

[Rixen]

The tolerances of some electrolytic capacitors are very loose aswell, they can be off by as much as -20% to +80%
that could maybe explain some of them.

Is there a problem with the casette player ?

 

[Michael/5of9]

The tolerances of some electrolytic capacitors are very loose aswell, they can be off by as much as -20% to +80%
that could maybe explain some of them.

Is there a problem with the casette player ?

The sound quality goes down as if the tape heads were dirty; I was told that the tape heads were long lasting and would't be the issue, it was likely to be the Electrolytic Capacitors (Elco's).

 

[duke37]

With simple test equipment how would I obtain this answer?

With a 4V capacitor as shown, measure the current going into it from two 1.5V cells in series.
Capacitor measurements are done with AC for smaller values but use a charge time for large electrolytics. See how your meter does it.

If the capacitor is leaky, the voltages could be low, generating distortion. Measure voltages across the transistors to check there is some headroom.

 

[Externet]

Before condemning those capacitors, check new ones and others you may have to confirm your meter is not reading higher. As above, they are usually +80% -20%, and do not blindly set your mind onto capacitors. Have you tampered with head azimuth setting ?

 

[Michael/5of9]

With a 4V capacitor as shown, measure the current going into it from two 1.5V cells in series.
Capacitor measurements are done with AC for smaller values but use a charge time for large electrolytics. See how your meter does it.

If the capacitor is leaky, the voltages could be low, generating distortion. Measure voltages across the transistors to check there is some headroom.

Test one; short out any stored electric before starting, I will be using my Fluke 73 meter; will 10 seconds connected be long enough to identify the test result?

Test two; see what voltage the cap then has.

As I haven’t done this before is my interpretation of your tests correct; I expect you will be wanting amps reading and volts reading?

 

[kellys_eye]

I was told that the tape heads were long lasting and would't be the issue, it was likely to be the Electrolytic Capacitors (Elco's).

As long as the tape heads may last, it doesn't follow that they are correctly aligned. A simple azimuth screw adjustment (left then right) will reveal whether or not the heads are 'out' as the higher frequency content will be very clearly heard as an improvement.

The suggestion that the capacitors are a cause is based on the fact that they don't age very well although those blue capacitors (usually made by Philips too as it happens) are pretty resilient.

The only 'proper' test for the capacitors would be for its internal series resistance (ESR) which isn't easy to check without the correct equipment - although such a tester can be had from Chinese sources for around £10.

So a simple screwdriver adjustment may alleviate all this unnecessary 'suffering'.....

 

[caps]

The transistor tester will show you three parameters. This is enough to evaluate the capacitor.

 

[Michael/5of9]

A very good day to you all and thank you for your valuable comments, well appreciated; it has become clearer now

Electrolytic Capacitors (cap) have a life span of around 1000 hrs; with this in mind, the higher readings are most likely acquired because of leakage from the old cap, as duke37 suggests.

With this in mind; it would make sense to replace them all, whilst the job is in hand. Below you can see the new cap and it’s capacitance reading.