You are here

Log in or register to post comments
CoolBeans
CoolBeans's picture
Offline
Last seen: Never ago
Joined: Oct 26 2007 - 10:49am
should I be worried?

I have just replaced some burnt resistors in my old kenwood amp and the new resistors get hot too. is this normal because the old ones that were installed in the factory were soldered away from the pcb.

thanks.

Jeff Wong
Jeff Wong's picture
Offline
Last seen: 3 years 9 months ago
Joined: Sep 6 2005 - 3:28am
Re: should I be worried?

It's possible the original (and replacement) resistors were inadequately rated in terms of wattage, and are overheating; you may eventually end up with burnt out resistors again. You could try putting in a higher rated resistor--you might have 1/4 watt or 1/2 watt resistors and the design might really require 1 watt resistors to comfortably handle the excess heat. My only concern would be if the sound became subtly altered with this/any substitution.

Jan Vigne
Jan Vigne's picture
Offline
Last seen: Never ago
Joined: Mar 18 2006 - 12:57pm
Re: should I be worried?

There is very likely a reason the old resistors were burnt. Look for problems upstream of the resistors particularly in the power supply. Components age and drift from their original spec which causes the circuit to change. Resistors as a rule are fairly reliable and they typically fail when another component taxes their specifications.

CECE
CECE's picture
Offline
Last seen: Never ago
Joined: Sep 17 2005 - 8:16am
Re: should I be worried?

MEASURE the current with a meter, then ya find out what size wattage resistor is needed. The wattage rating of a resistor is not going to any effect on the sound, how can it? The resistance value being the same. Wattage ratings has to only do with teh power it can disapate safely. Depending on what TYPE resistor it is, also many are made to run warm or hot.

absolutepitch
absolutepitch's picture
Offline
Last seen: 1 year 1 month ago
Joined: Jul 9 2006 - 8:58pm
Re: should I be worried?

All good suggestions, except that I would check it out as Jan suggested. Something is causing the resistor to overheat, and you have to solve that problem first. Putting higher wattage resistor is like putting higher amp fuses in your house if the fuse keeps blowing. Don't do that before knowing the rest of the circuit is operating normally.

I have an oscilloscope in which the high-voltage transformer started smoking. The problem was trace to a shorted capacitor. Replacing the capacitor blocked the DC from shorting to ground and the transformer no longer smoked.

Jeff Wong
Jeff Wong's picture
Offline
Last seen: 3 years 9 months ago
Joined: Sep 6 2005 - 3:28am
Re: should I be worried?

It makes much better sense to find the cause rather than treat the symptom; my suggestion (perhaps) wrongly assumed the circuit was performing as designed.

CoolBeans
CoolBeans's picture
Offline
Last seen: Never ago
Joined: Oct 26 2007 - 10:49am
Re: should I be worried?

thanks for all the helpful advice. when I was replacing the resisters I was thinking of replacing the caps too. did anybody ever find that as a problem to overheating resisters? I would have measured them but my cheep meter does not measure capacitance. its funny that when I sprayed refrigerant on all the resisters in this amp the only bad ones were on the power board.

Jan Vigne
Jan Vigne's picture
Offline
Last seen: Never ago
Joined: Mar 18 2006 - 12:57pm
Re: should I be worried?


Quote:
when I was replacing the resisters I was thinking of replacing the caps too. did anybody ever find that as a problem to overheating resisters?

Components age and drift from their original spec which causes the circuit to change. Caps are typically the first component to be replaced in a restoration or repair project. This would be particularly true of power supply caps which block DC voltages where they are not desired and feed the correct voltage (when the cap is operating properly) to the rest of the amplifier's circuitry. If the Marantz receiver you picture is your restoration project, you might have more problems than power supply caps.

cyclebrain
cyclebrain's picture
Offline
Last seen: 2 months 1 day ago
Joined: Jun 16 2006 - 11:40pm
Re: should I be worried?

You refer to the resistors as "burnt". Does this mean that they have failed or their value has changed, or that their appearance has become brown? The resistors were probably mounted away from the board to provide more airflow.

cyclebrain
cyclebrain's picture
Offline
Last seen: 2 months 1 day ago
Joined: Jun 16 2006 - 11:40pm
Re: should I be worried?


Quote:
This would be particularly true of power supply caps which block DC voltages where they are not desired and feed the correct voltage (when the cap is operating properly) to the rest of the amplifier's circuitry.


Sorry Jan but the power supply caps are not used to block the D.C. voltage in this case (a series cap), but instead to smooth out the 120Hz rectified line power by storing energy (a parallel cap). They are also used to shunt unwanted noise to ground.

Jan Vigne
Jan Vigne's picture
Offline
Last seen: Never ago
Joined: Mar 18 2006 - 12:57pm
Re: should I be worried?

Yes, I know. That's why there's an "and" in there.

  • X
    Enter your Stereophile.com username.
    Enter the password that accompanies your username.
    Loading