Capacitor help please

Thread Starter

daveyhouse

Joined Feb 3, 2007
6
This is what I can read off of it

MED
C471
R3.2-5.2? <cannot make out that symbol
125V

This item connected a coax lead to the tuner on a tv
 

thingmaker3

Joined May 16, 2005
5,084
No clue about "MED" save that the M in three leter capacitor codes often means "metallic."

"C471" = "470 picofarads, plus or minus one quarter picofarad."

"R3" by itslef would mean "made in March of 2003." I don't know it such is the case here.

"125V" means "rated for a maximum of 125volts." Since AC is not specified, assume 125 volts DC (max 88 volts AC).
 

Thread Starter

daveyhouse

Joined Feb 3, 2007
6
thank you for the response thingmaker3.

I went to rat shack picked up a set this morning she said it "should" work
472K
500WVDC MAX
0.0047uF
http://www.radioshack.com/product/index.jsp?productId=2102418&cp

Okay we can see channels now, but they are snowy. So I guess this item will not work.
I see that they also have another @50v would I be better trying one of these? http://www.radioshack.com/product/index.jsp?productId=2062364&cp=2032058.2032230.2032267&allCount=100&fbn=Type%2FCeramic+Disc+Capacitors&f=PAD%2FProduct+Type%2FCeramic+Disc+Capacitors&fbc=1&parentPage=family

Thanks Again,
Dave
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

What led you to suspect/replace that capacitor? Usually, only some disaster with lightning will cause one of them to fail, and by then, the rest of the tuner is toast.

One of the semiconductors is a more likely cause of the failure than a passive component.
 

Thread Starter

daveyhouse

Joined Feb 3, 2007
6
Okay here is the scenario.
This one of my childrens tv sets. They are always moving things around. I guess they over tightened the cable coax and twisted the thing right out of its base. So I took it apart to solder back together. I got the fitting back on securely but capacitor legs were also torn off. No electrical damage, just physical.

Update: I think the reason for the snowy picture is due to a resistor that connects to the coax shielding. When I tested with multi-meter, I did not get any reading. So I guess that means it is totally open.

The colors on this were grey, red, green, silver. = 8.2 Mohms yes? (web calculator) (I love google)
What is the M for? million?

Anyway when I inserted the coax lead wire without connecting the shield I have snowy picture, I then connect the shield and nothing changes. That is what made me follow the shield path.

Thanks again, your forum is awesome.
Dave
 

thingmaker3

Joined May 16, 2005
5,084
This is why I never go to Rat Shack! 470pF=0.00047uF, not 0.0047uF. Any source on the planet other than Rat Shack would have a card hanging handy to make conversions. Arrrgh! :mad:

Sorry. Rant over now... :(
 

mrmeval

Joined Jun 30, 2006
833
Televisions have very critical AC isolation on any metallic protrusion. In some sets the isolation is provided by a switched mode power supply.

In a television that has a "hot chassis" where raw AC is rectified, filtered and sent to a linear regulator (or in some cases a type of smps that does no isolation) the AC and DC usually share grounds. Isolation in those televisions is provided by special capacitors and a metal box that has the RF connector on it which then plugs into the tuner. Anything that compromises this isolation can place line voltage on the coax connector. This can electrocute you or your children though it is most likely to short the AC to ground and blow the bridge rectifier and fuse when you attach the coax and plug it in.

In some sets the box will be a box that has a cable plugged into the tuner with the box mounted on the back of the set. Others the box has no cable and the tuner is close enough to the back for the RF connector to fit through. If the RF connector goes into the back of a large rectangular box you may be ok. ...

That device may be a capristor

This is about all I could find to point out what I'm saying.
http://www.patentstorm.us/patents/5351018-description.html

http://www.epanorama.net/links/repair.html
Don't have the TV hooked to anything except the power when you do this.

AC leakage: Connect a 1.5K ohm, 10 Watt resistor in parallel with a 0.15 uF, 150 V capacitor to act as a load. Attach this combination between the probes of your multimeter. With the equipment powered up, check between a known earth ground and each exposed metal part of the equipment as above. The potential measured for any exposed metal surface must not exceed 0.75 V. This corresponds to a maximum leakage current of 0.5 mA. A true RMS reading multimeter should be used for this test, especially where the equipment uses a switchmode power supply which may result in very non-sinusoidal leakage current.
I had one of these made up for "quick and dirty" testing a long time ago.
 

Thread Starter

daveyhouse

Joined Feb 3, 2007
6
mrmeval, thank you for those links. Very informative.

I guess I am 86'ing this project. I replaced the cap and resistor, found an old local man that had pieces that I needed.

Snowy picture remains. It is only when it is hooked up to local cable company. If I hook an OTA antenna the picture is clear. Go figure

Thanks
Dave
 
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