Sencore LC53 leakage test acting up?

Shakedown

Shakedown

Active Member
I am attempting to test these caps under an HH Scott amp for leakage. I have the Sencore set to "All Other Capacitors".

So far I have used the leakage test on two caps, for one it gives no reading on any voltage selected and just stays on zero. Dropping down the the light to uA, made sure one end was soldered off the board.

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The next cap I decided to test for leakage was I assumed rated for 25v DC, however the Sencore meteter continuously blinks past applied 3v. When 3v is selected, only then does it give me some sort of reading that begins to drop.

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Only problem is, it's not supposed to be a 3v cap and won't allow me to test any further. Is this of any indication that the Sencore is broken, or just bad caps?
 
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Alright, changed my fuse but no dice.

Does anyone know if the leakage test is supposed to be testing for voltage or capacitance?
 
A leakage test applies the rated voltage dc to one end of the cap and uses an ammeter to ground to measure the leakage current. Leakage current across a load shows as voltage. Anything besides 0 is a bad csp.
 
trainbuftony said:
A leakage test applies the rated voltage dc to one end of the cap and uses an ammeter to ground to measure the leakage current. Leakage current across a load shows as voltage. Anything besides 0 is a bad csp.
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Would you happen to know what blinking past three volts indicates, the machine itself won't allow me to set a voltage beyond that without flashing zeros.
 
I presume you don't have a manual for this thing or a schematic? Maybe the manual would explain that error code.

You could open it up and look for obviously burnt components but that's a crapshoot.
 
NAD80 said:
Hello Shakedown. Found the manual if you need it. http://bama.edebris.com/manuals/sencore/lc53/ . Those caps look old enough to be bad. Check out this web page on replacing caps. https://antiqueradio.org/recap.htm . Have one at work. Doesn't get used often.
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Thanks, definitely a few original caps in there.

Here is a the full picture, it looks like someone went in and did a full restoration at one point in it's life.

Only one bumble bee cap left, if this was done say fifteen years ago I would hate to tear up the job as these 121c's are a bit more on the difficult side.

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I found this...

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That cap I measured was .022UF 400v which would be 20000pF, not below 1000 pF.

Only sure way to test this, would be to grab a brand new 200v or so capacitor. It does give off a correct value, just won't allow me to apply any voltage past three volts on the leakage test.

The manual only indicates a blown fuse could be the culprit, so I went ahead and swapped out a fresh one but problem remains.

I will probably sell it for parts and try my hand at a fully tested unit, I opened up the Sencore and it sure is an intricate piece of machinery.
 
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When I test large electrolytic with mine, if the leakage value exceeds 9999microamps it will flash 888.
 
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I should have the setting at "all other capacitors", that's what I believe I am doing correctly.

This should be alright for testing .022uf caps correct?
 
Don't know that tester, but all micas and films should show no leakage. Many old electrolytics will have moderate to high leakage- those are the ones where the test info is useful. Most new electrolytics will show some value that then falls slowly to under 10 uA. Decent small values will fall to under 2 uA.
 
I don't know that machine, but given that the second cap is a polar electrolytic, it likely exceed the range of the testers ability. It is trying to tell you that cap is a dead short (A giant leak). This is a guess based on my experience using a cap tester which I built myself. Testing old electrolytic caps it often times maxes out the ammeter, slamming the needle to maximum. Blinking LED lights are the "modern" way of saying "hey don't do that"! Hopefully someone chimes in with some experience on that machine. Bias caps like the 25, 25 should be replaced based on their age and composition, and it wouldnt surprise me if the tester was trying to show them as leaky.
 
Just for informational purposes, clip a resistor in the leads of the cap tester and test it. This should show loads of leakage current (simulating a completely shorted capacitor) because resistors don't block DC. If the cap tester does the same thing (blinking display) then you know that the blinking display means a completely shorted cap. Put that cap in the waste basket do not pass go and pay Mouser $7.99 for shipping...
 
trainbuftony said:
I don't know that machine, but given that the second cap is a polar electrolytic, it likely exceed the range of the testers ability. It is trying to tell you that cap is a dead short (A giant leak). This is a guess based on my experience using a cap tester which I built myself. Testing old electrolytic caps it often times maxes out the ammeter, slamming the needle to maximum. Blinking LED lights are the "modern" way of saying "hey don't do that"! Hopefully someone chimes in with some experience on that machine. Bias caps like the 25, 25 should be replaced based on their age and composition, and it wouldnt surprise me if the tester was trying to show them as leaky.
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Interesting to note, what would be the capacitance rating on that second yellow cap which is not printed on the label. All I can see is it's voltage at 25DC, I'll be needing to replace it.

I have a fresh 100v capacitor arriving in the mail on Monday for testing, too bad I don't have Radio Shack around here any longer. I am tempted to take this Sencore off eBay, if it truly may not be broken.
 
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It looks like a 25uf 25 volt bias cap, but I could be wrong. Where was it located in the circuit? Was it between ground and the cathode of one of the tubes? I looked at several Scott preamp schematics online and several of them are using a 25 microfarad electrolytic on the cathode of one, or more of their tubes. I would say it is safe to assume it is a 25uF 25v electrolytic. One of the parts that the HH Scott company must've bought in bulk...

Also: Sweet turntable. My good friend Brought me a heavily nicotine stained 208 he found in the trash and it is now my main go to table. He found it next to a HH Scott model 208 power amp which is also loving it's new lease on life playing music in my system. Literally on the curb, on trash day.
 
Shakedown do you have a new cap to check?. The sencore will flash when the leakage is higher than the range selected. Given the fact that you cannot go higher in voltage than 3vdc, I would say the cap is shorted. A good cap will be able to handle it's working voltage. I think the sencore is working like it should. Do you have a meter? You could put the meter across the cap in resistance mode to see if it is shorted. A cap as it charges up will go up in resistance till it reads in the meg-ohm range or open. Also you could connect the sencore to the meter in the vdc range to measure the voltage applied, without the cap in the leads. One way to see if it applies more than 3vdc. Set the meter in the 100 vdc range. I'd have to check the one I have at work to see what it does under the same conditions. The film cap should show no leakage if good. The paper type could go shorted if the leakage is super high.
 
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