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#1
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Tom: The hot cap has two likely possibilities: either the cap is shorted internally (an ohmeter check will show leakage) or you have bad diode(s) so AC is being applied to the cap. An ohmeter will show the diodes as bad. Of course a wiring error could also be involved, but I am assuming you have double checked that. If the cap is running hot you probably don't have the correct voltage for the VFO, and correcting it may solve the other VFO problem. Roger K6XQ |
#2
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#3
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Active8 wrote:
In article , says... Tom: The hot cap has two likely possibilities: either the cap is shorted internally (an ohmeter check will show leakage) or you have bad diode(s) so AC is being applied to the cap. An ohmeter will show the diodes as bad. a backward diode will supply AC to the cap, also No, it won't. It will however supply the wrong polarity of DC, which could indeed cause these symptoms. I would think some other semiconductors might be running rather hot too if that were the case. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
#5
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If you're using a diode bridge like most people do these days, and the
diode bridge output terminals (+ and -) are reversed, the filter capacitor would get hot and the receiver wouldn't work. As others have pointed out, an electrolytic capacitor with reverse voltage applied can catch fire or explode. Be careful when troubleshooting while the capacitor is unhappy. When you do find the problem, it would be a good idea to replace the capacitor. Roy Lewallen, W7EL Active8 wrote: In article , lid says... Active8 wrote: In article , says... Tom: The hot cap has two likely possibilities: either the cap is shorted internally (an ohmeter check will show leakage) or you have bad diode(s) so AC is being applied to the cap. An ohmeter will show the diodes as bad. a backward diode will supply AC to the cap, also No, it won't. oops. right. 1 diode backwards in a full wave (not a bridge) rectifier would short the xfrmr. It will however supply the wrong polarity of DC, which could indeed cause these symptoms. I would think some other semiconductors might be running rather hot too if that were the case. |
#6
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In article , says...
If you're using a diode bridge like most people do these days, and the diode bridge output terminals (+ and -) are reversed, the filter capacitor would get hot and the receiver wouldn't work. As others have pointed out, an electrolytic capacitor with reverse voltage applied can catch fire or explode. Be careful when troubleshooting while the capacitor is unhappy. When you do find the problem, it would be a good idea to replace the capacitor. i've had a couple explode, usually from overvoltage from a shorted series pass reg, i think. nice thing about (some? most?) electrolytics is that X that's scored into the top so it blows straight up. i'm glad my face wasn't over top of it, though. even with safety glasses, it's not something i'd like to experience. mike c Roy Lewallen, W7EL Active8 wrote: In article , lid says... Active8 wrote: In article , says... Tom: The hot cap has two likely possibilities: either the cap is shorted internally (an ohmeter check will show leakage) or you have bad diode(s) so AC is being applied to the cap. An ohmeter will show the diodes as bad. a backward diode will supply AC to the cap, also No, it won't. oops. right. 1 diode backwards in a full wave (not a bridge) rectifier would short the xfrmr. It will however supply the wrong polarity of DC, which could indeed cause these symptoms. I would think some other semiconductors might be running rather hot too if that were the case. |
#7
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In article , says...
If you're using a diode bridge like most people do these days, and the diode bridge output terminals (+ and -) are reversed, the filter capacitor would get hot and the receiver wouldn't work. As others have pointed out, an electrolytic capacitor with reverse voltage applied can catch fire or explode. Be careful when troubleshooting while the capacitor is unhappy. When you do find the problem, it would be a good idea to replace the capacitor. i've had a couple explode, usually from overvoltage from a shorted series pass reg, i think. nice thing about (some? most?) electrolytics is that X that's scored into the top so it blows straight up. i'm glad my face wasn't over top of it, though. even with safety glasses, it's not something i'd like to experience. mike c Roy Lewallen, W7EL Active8 wrote: In article , lid says... Active8 wrote: In article , says... Tom: The hot cap has two likely possibilities: either the cap is shorted internally (an ohmeter check will show leakage) or you have bad diode(s) so AC is being applied to the cap. An ohmeter will show the diodes as bad. a backward diode will supply AC to the cap, also No, it won't. oops. right. 1 diode backwards in a full wave (not a bridge) rectifier would short the xfrmr. It will however supply the wrong polarity of DC, which could indeed cause these symptoms. I would think some other semiconductors might be running rather hot too if that were the case. |
#8
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If you're using a diode bridge like most people do these days, and the
diode bridge output terminals (+ and -) are reversed, the filter capacitor would get hot and the receiver wouldn't work. As others have pointed out, an electrolytic capacitor with reverse voltage applied can catch fire or explode. Be careful when troubleshooting while the capacitor is unhappy. When you do find the problem, it would be a good idea to replace the capacitor. Roy Lewallen, W7EL Active8 wrote: In article , lid says... Active8 wrote: In article , says... Tom: The hot cap has two likely possibilities: either the cap is shorted internally (an ohmeter check will show leakage) or you have bad diode(s) so AC is being applied to the cap. An ohmeter will show the diodes as bad. a backward diode will supply AC to the cap, also No, it won't. oops. right. 1 diode backwards in a full wave (not a bridge) rectifier would short the xfrmr. It will however supply the wrong polarity of DC, which could indeed cause these symptoms. I would think some other semiconductors might be running rather hot too if that were the case. |
#9
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In article , lid
says... Active8 wrote: In article , says... Tom: The hot cap has two likely possibilities: either the cap is shorted internally (an ohmeter check will show leakage) or you have bad diode(s) so AC is being applied to the cap. An ohmeter will show the diodes as bad. a backward diode will supply AC to the cap, also No, it won't. oops. right. 1 diode backwards in a full wave (not a bridge) rectifier would short the xfrmr. It will however supply the wrong polarity of DC, which could indeed cause these symptoms. I would think some other semiconductors might be running rather hot too if that were the case. |
#10
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Active8 wrote:
In article , says... Tom: The hot cap has two likely possibilities: either the cap is shorted internally (an ohmeter check will show leakage) or you have bad diode(s) so AC is being applied to the cap. An ohmeter will show the diodes as bad. a backward diode will supply AC to the cap, also No, it won't. It will however supply the wrong polarity of DC, which could indeed cause these symptoms. I would think some other semiconductors might be running rather hot too if that were the case. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
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