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cap test

 
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cap test

Post by rob t » Tue Aug 02, 2011 1:38 pm

Image
strange one this capacitor checkes out fine but after 5 mins causes hum in the amp it came from.repacment cured the fault
is there any othe test that is more reliable?
robt

 
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Post by crustytv » Tue Aug 02, 2011 1:48 pm

Hi Rob,

As Trev states under load conditions it's failing. If your up for it send it to me I would be interested to pop it on the Bridge set up and see what gives.

Chris
Last edited by crustytv on Tue Aug 02, 2011 2:18 pm, edited 1 time in total.

 
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Post by rob t » Tue Aug 02, 2011 3:03 pm

if i find time i will send it to you chris.
i allso checked it on my taylor rc bridge
it confused me because elna caps are nornaly good, at£14 each they are to expensive to keep in stock
many thanks for replies
rob t

 
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Post by crustytv » Tue Aug 02, 2011 3:08 pm

Hi Rob,

Did the Taylor show any signs of leakage when rated voltage was applied?

I did a bit of digging a round as quite a few people have found ESR meters have difficulty sometimes detecting bad caps.

I also found this which might give you another test option

An old time radio engineer taught me a way to test electrolytic capacitors that is pretty much infallible once you get accustomed to it. He takes the square wave "cal" output of his scope into one of its vertical inputs with a coax jumper and a BNC "T" adapter. A "straight" (1:1) probe is connected to the third leg of the "T." With the probe open-circuited, the scope is adjusted to give a comfortable display of the cal signal. He then connects the probe and ground lead to the capacitor.

What you see on the screen is, a good cap will drag the square wave down to almost nothing. An open cap will leave the square wave practically unchanged. Caps with high leakage or ESR will reduce and distort the square wave, but not cancel it completely. If in doubt, a brand-new cap of the same size can be measured on the bench to see if there's any difference.

My modification on it is to use a separate pulse generator with a 47-Ohm resistor in series with its output. This allows me to "see" what the caps are actually doing at different frequencies.

Chris

 
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Location: gloucestershire

Post by rob t » Tue Aug 02, 2011 4:25 pm

no leakage shown on the bridge
using the scope would be a good idea.
i wont go into the hours spent on this amp because i was shure the smoothers were ok
rob t

 
Posts: 1450
Joined: Wed Jul 27, 2011 10:14 am
Location: gloucestershire

Post by rob t » Tue Aug 02, 2011 11:36 pm

thats an interesting i dea ihave a 2 watt vale amp i built so run from my funtion gen would be worth experimenting with. i dont think a solid state amp woul like 10000mf across its output,or i could put it in series with an 8 ohm 10 watt resistor.iwill have a go in the next few days
rob t


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