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A while ago I posted a thread on diagnosing a channel imbalance problem I was having on a vintage Harmon Kardon 330 receiver. One respondent suggested the following as a way of diagnosing/fixing the problem since I did not want to send the unit out to a tech:
“I agree that the most likely culprit is a bad capacitor, but another possibility is a resistor whose value has wandered (gotta love carbon comp resistors).
To the original poster: The parts cost of fixing this amp will be minimal, a few dollars at most. If you can solder, but aren't strong on diagnosis, you could replace the capacitors and resistors in and around the tone control circuitry.
Even if you don't have a schematic, but do have a meter, you could compare the components in the two channels and replace anything that is significantly (20% or so) different in the bad channel.”
I am very green in the DIY area and am taking this project on as a learning experience. My question is how do I use a multimeter to perform the above testing? Which setting do use on the multimeter? FYI, I am using a cheap Sperry multimeter from Home Depot which I had bought for another project.
I assume I am taking the reading when the unit is not plugged in for power. Is this correct?
When measuring a capacitor/resistor, where do I touch the red and black leads of the multimeter?
In determining if a capacitor/resistor is bad, the value I measure is compared to what? The value written on the capacitor/resistor?
Any other tips or suggestions?
Thanks for any assistance you can provide.
Patrick
Follow Ups:
The probability of it being a resistor is low, it is more likely to be a cap.An inexpensive handheld, even if it has capacitance, is of little use.
I would take a 100uF 100V non-polar cap and hook the meter test probes to it.
Parallel each cap with the test cap, shorting out the cap before moving on to the next.
If you like the receiver, you would be advised to order all new caps from a place like Digi-Key (they are not expensive).
Is it a 330, 330B, or 330C ?
Edits: 10/21/09
djk,
Thanks for the response. The receiver is just a HK330, not the B or C versions.
HK schematics (330A is in the 330B file).http://manuals.harman.com/HK/service%20Manual/HK330B%20sm.pdf
http://manuals.harman.com/HK/service%20Manual/HK430%20sm.pdf
http://manuals.harman.com/HK/service%20Manual/HK630%20sm.pdf
http://manuals.harman.com/HK/service%20Manual/HK730%20sm.pdf
http://manuals.harman.com/HK/service%20Manual/HK930%20sm.pdf
Edits: 10/21/09
Hi DJK,
I try using 'http://manuals.harman.com/jbl/' but not be able to get the site. I also try using 'http://manuals.harman.com' with no luck. I was able to download JBL before. How did you do it? Thanks
"How did you do it? "Guessing, mostly. Contact HK for ones you can't figure out.
Another handy one:
http://www.jblpro.com/search_23.htm
Edits: 10/22/09 10/22/09
Maybe bother to Read the Instructions that came with the meter? Inexpensive multimeters will likely not have Capacitance measurement capability, but should have Resistance settings (several ranges, select the range that suits the part being measured). To check resistors, power to the device being measured must be OFF, place either probe (makes no differance with this particular measurement) on one side of the resistor & the other probe on the other side, view the meter display. Compare result to value & tolerance as marked on resistor (often via color bands which require Standard decipher). Be certain other circut pathways are not in parallel with the part being measured or false readings will result.
Edits: 10/20/09
"Inexpensive multimeters will likely not have Capacitance measurement capability, but should have Resistance settings (several ranges, select the range that suits the part being measured)."
Your looking for the OHM setting on your meter looks like an upside down horseshoe, actually the Greek letter Omega.
"To check resistors, power to the device being measured must be OFF, place either probe (makes no differance with this particular measurement) on one side of the resistor & the other probe on the other side, view the meter display. Compare result to value & tolerance as marked on resistor (often via color bands which require decipher). Be certain other circut pathways are not in parallel with the part being measured or false readings will result. ."
If you need to check a resistor or cap in line you will probably have to lift one end. This will insure your not reading through the rest of the circuit. You will only be able to tell if a cap is shorted or open though. Normally a good cap will read a very high resistance. You'll read low if resistance if it is shorted and infinite if it is open
Since most Ohms readings are taken via passing the meters's internal Battery current thru the resistor under test, attempting similar evaluation on a capacitor will charge the capacitor = a false reading if you're not very experienced at doing so.
Wow,I am new to this. I had pretty much the same question,thanks for the info.
while a capacitance meter can show correct capacitance, the cap may still be bad. An ESR (Equivalent Series Resistance) meter may be required to assess the cap's state.Also as others mentioned, you would need to unsolder one end of each resistor before taking the readings, otherwise you are measuring the resistor's value in parallel with the resistance of the circuit it's connected to.
and keep in mind that large capacitors can store charge for while after the unit is powered off. It is good practice to keep one hand in your pocket with doing such testing (especially for tube stuff!) so that you don't become part of the circuit!
Edits: 10/25/09
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