help troubleshooting amplifier/receiver please

[JMB]

I inherited an old JVC receiver ("Super A amp"). When I turn it on there is a loud crackling sound that comes through the speakers and continues. The music signal (say from a CD or the tuner) still comes through but it seems to be with decreased volume. Any suggestions on what I should start to look for? This troubleshooting attempt will be a new experience for me but I can recognize components and have and LCR and a DMM.
Thanks in advance.

 

[anatech]

Hi JMB,
Now, if you had a 'scope ...

Does this unit have pre out / main in jacks? If so, use a preamp and feed a signal into the main in (or amp in ) jacks and have a listen. You can feed the pre out into another receiver's input and turn the volume up on the suspect unit to test. Now you've split the unit in half for troubleshooting.
Try pushing the switches in & out slowly while listening for static. Tap the speaker relay while listening. These tests will probably show some contacts that need cleaning. Do not use tuner cleaner!
The above tests catch at least 80% of faults. You really could use an oscilloscope and sine wave generator to dig out the tougher faults.
-Chris

 

[gmphadte]

audio tracer, a crystal receiver...

for analog audio circuits only...
You have to listen to the audio in the circuit and find the faulty stage.

The simplest and the cheapest way is a crystal receiver. When the hearing is good and the surrounding is quiet, u can even hear audio signals directly on the tape head. Since it is a high impedance earphone, u don't have to worry about loading effects.

Start at the input and proceed towards the output.
Find the distorting stage and then find the culprit(defective component).

Remember-SAFETY FIRST

Gajanan Phadte

 

[anatech]

I wouldn't call a "2K high impedance" earphone truely high impedance for signal chasing. You can use a small amplifier coupled with a small capacitor, but this will only show you distorted / not badly distorted. An oscilloscope will tell you much more without loading the circuit. See if you can hook up with someone with access to a 'scope if switch or relay contacts are not to blame.
Chris

 

[Netlist]

Yet nobody asked for the type number.

/Hugo

 

[anatech]

Hi Hugo,
Well, we are hoping to hear from JMB again. A model number may help if someone has experience with that exact model. So far, suggestions are general, as requested.
-Chris

 

[JMB]

Thank you so much for responding. I just had a baby so I have been a little tied up. The model is JVC RX-44. There is no pre-amp out. I haven't yet had the chance to open it up to begin the troubleshooting process but I hope to get to that during the next couple of weeks. Just tough to find time right now. I welcome any additional suggestions for when I do get to it.

Thanks again,

Jay