Difficulty Identifying a Component from Circuit Board

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prcguy

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You will find a compatible part on Ebay, I just bought some similar caps there.
prcguy

That was my thought, too.

Try finding someone that still fixes these things, and ask them if they would sell you the part. There should be an identifier on that board, for that part. It should be Cxxx, where the xxx is a number. (That can be looked up in the parts listing of the service manual, and should give the values for that part.)

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RFI-EMI-GUY

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I would like to pretend I know what that means, but I honestly do not.

Some folks who work on vintage gear have an isolation transformer on the bench to plug vintage stuff into so they won't get shocked on their butt. Also popular is a variable transformer a variac, used to bring the voltage up slowly on stuff unused for decades. Both these items can cause a lot of voltage surge when testing equipment with relays and motors.
 
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I am fairly new to this. I only learned how to use a soldering iron in the last 6 months lol. I want to be sure I put the right part back in so I don't destroy anything, but I don't have enough faith in myself to do it without confirmation from someone else that it is the correct part.
 
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Thanks for the help everyone. I ordered 10 400v, 0.1uF capacitors on Amazon. They seem to be the same part that came out, and also a 10 pack was only $5 lol. I am on a tight budget like everyone else. I will let everyone know how it works out when I get a new one installed.
 

jonwienke

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Capacitor ratings generally refer to peak allowable voltage.
 
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It says for use in pulse circuits, the ones in the link above said they were used in pulse circuits. So I just assumed that is what I need.
 

pro92b

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Capacitor ratings generally refer to peak allowable voltage.

No, it's not that simple. A 400VDC rated capacitor connected across a 240 VAC line will fail in a few weeks due to AC corona vaporizing the metallization. Even a 600VDC rated capacitor will fail similarly if connected to 240 VAC.

The attached file discusses this issue for those interested.
 

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jonwienke

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Peak voltage is √2 * RMS voltage. So for 240 VAC, the peak voltage is just under 340V. You don't want the peak voltage to continuously approach the maximum rated voltage, just like you don't want to run any component near any other absolute maximum rating, whether current, ambient temperature, etc.
You also want a fudge factor for surges on power circuits. But if the original capacitors were rated for 400V, then replacing them with a part rated at 400V should be fine, as long as all other parameters match.
 

pro92b

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You miss the point. It is not clear if the original capacitor is AC or DC rated. For that matter most of the posts in this thread are speculative without a schematic or service manual to define what the capacitor rating is and what it does in the circuit. The service manual for this equipment is available but at a price. I was not able to find one to download for free.
 

prcguy

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Who says the capacitor is used across the AC line? It might be used at 24V or 12V or ??
prcguy



No, it's not that simple. A 400VDC rated capacitor connected across a 240 VAC line will fail in a few weeks due to AC corona vaporizing the metallization. Even a 600VDC rated capacitor will fail similarly if connected to 240 VAC.

The attached file discusses this issue for those interested.
 

pro92b

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Who says the capacitor is used across the AC line? It might be used at 24V or 12V or ??
prcguy
Maybe. But with a 400V rating and enough circuit energy to make it smoke, it's probably more than 24V. Without more info it's all guessing as I said before.

Film capacitors are not polarized whether DC rated or AC rated. Sometimes the outer foil is marked with a line. It can be an advantage to connect the outer foil to the potential closest to ground in some circuits. Some examples are below: the top two have no polarity mark, the TRW outer foil is connected to the left lead, the green cap has no polarity mark and the bottom cap is AC rated and safety approved.
 

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Wow. I had no idea simply asking for help would produce both an argument and criticism of my photographic ability. From this point forward I will be sure to figure things out on my own.
 

AK9R

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Asking a technical question in a public forum is a two-way street.

The OP has to provide enough information for the respondents to provide reasonable answers.

The respondents need to understand that the OP may not have the knowledge, experience, or skills that the respondents have.

If you can't provide a helpful answer, and I've already deleted two posts that contributed little to the thread, then just move on. Those who are trying to help, please be patient.
 
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Based on my own research as well as the help of some here, I replaced the part in question, and 6 identical others on that board, and all seem well. I have it playing a 1966 vintage Floyd Cramer tape right now. No smoke, running like a top. Hopefully it stays that way.
 

prcguy

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It could be the original part was operating safely within its ratings, but the capacitor was 47 years old. Things fail. Congrats to the OP for bringing it back to life.

Maybe. But with a 400V rating and enough circuit energy to make it smoke, it's probably more than 24V. Without more info it's all guessing as I said before.

Film capacitors are not polarized whether DC rated or AC rated. Sometimes the outer foil is marked with a line. It can be an advantage to connect the outer foil to the potential closest to ground in some circuits. Some examples are below: the top two have no polarity mark, the TRW outer foil is connected to the left lead, the green cap has no polarity mark and the bottom cap is AC rated and safety approved.
 
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