Loud pop sound at anytime in left channel Pioneer A-9

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#21
I have one more question
. If speaker A switch is on even though there is no speaker attached to it and the pop still occurs on the speaker s attached to the speaker B set while B is also on . Does this mean speaker A relay is bad and inspite of that the pop sound interferes with speakers relays connected on set B with speakers connected ?

Now I am doing a test with speakers A set off and only speaker B set is ON with speakers connected to speaker B set only . Hope you understood my question and if this is the issue I would be happy . Still testing. Have to wait almost a day to know for sure .
 
#22
A and B is connected to the same circuit ,the amplifier .
if you want determine if the relais are defective,you can desolder all and solder and a jumper under the pcb.
but I have never seen any relay create pop in the hp, that does not mean that it is not possible
 
#23
Thanks for the information huggygood and every one here . Good forum . Reason I had asked if relays can create this sort of issue is because I came across it in this forum. Help! - noise problem on vintage Pioneer receiver | Steve Hoffman Music Forums

I am hoping it's the same thing . I am now waiting until system gets in cold state then I will switch it ON and see . I am testing it with speakers set A off and speakers connected to speaker set B and B will be ON
 
#25
Here is how I get the pop . After its cooled down completely . That is when I keep the system off overnight for 8 hours . I wake up in the morning switch it ON . Immediately after the relay kicks in ok about after 1 min you can start to hear some very low scratching sound in left channel (speaker set A ) and then pop, a loud one . And followed by another pop after maybe 10 secs and that's it . Then maybe it would pop after 1 hour random or maybe it won't . Then after some more time it may pop . I noticed it need to be completely cool to test as in it should be left OFF for several hours to turn on and test again . In my case I try to fast forward the process . I cool it down naturally in the off mode just leaving it ther off . Then I put it under the air-conditioner about 10 feet away direct drift for coolness . I do it for about 30 mins then I switch off the AC and wait another 45 mins and turn ON the system . This is how I get frequent pop sounds . In the complete cooled down way .

So now I switched the speaker s to set B and waiting until the unit is cooled completely .
 
#26
Speakers are not a complex matter here. If an output has been disconnected from the speakers, it also doesn't matter what the relay does then, because it won't be making or breaking connection to any circuit that could generate noise. See output schematic below.

I have query regard to your videos though; are the pops you refer to the same type of noise as you show on the graphic display where you operate the switch?
 

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#28
No the pops are not the same . In the sense the random pop which occurs on its own without touching the system is very very loud in output and frightening.the left VU meter goes all the way up . The video where I am manually turning the bass control for similar pop sound is lower much lower in sound output .so i am convinced that the bass control knob is not the issue.

Now I am testing the system . I just wish I had some alone time . With the family at home it becomes difficult for me to stay in the same room for extended period s of hours as I test and spend lots of time for such issue
 
#29
Yes I too was also looking at that part of the schematic an hour ago . I was trying to understand if those two relays are the ones that go off when ever there is a problem in the amplifier generally .( The red light protection ) I am under the impression there is one relay for protection circuitry and two more relays for speaker relay (set A and B . Or am I wrong ?
 
#30
Also I am concerned about the DC off set . I really wish I could check the DC off set as I feels it is important but unfortunately my meter is not working and I don't have a spare. I am more comfortable with the analogue meter s . I can feel a low current in auxiliary wire when it's connected to the system ( I know there is current as I can feel it with my fingers) . And one of the speakers wires at the end too there is some current flow even with the system OFF. Is this related to DC offset . I know the tech set that up the last time I gave it for repairs back in 2014
 
#33
Yes, those larger power relays are needed to handle the output and fault currents. There are only 2 because the idea behind older protection schemes is simply to disconnect all speakers first to prevent damaging DC at high fault currents from reaching them. Just cutting power to the speaker relays does exactly that, so long as they are rated high enough to open reliably when needed.

Look at the block diagram - There are only the 2 power relays but the schematic shows a lot more small ones associated with the volume control, headphones, subsonic filter, phono preamp, and more. These are not for protection but signal control switching. It must sound like a whole chorus of clicks when you power the amplifier or make adjustments though.

The only remaining protection is fuses in the amplifier power supply and they may or may not be fast enough to protect much, other than the power transformer.
 
#36
thanks @huggygood . Hope you have the full version . its about 4.09mb file size . At least thats what I have.

Yes @Ian Finch, thanks for confirming about the speaker relays. That makes sense . Correct. there are somany other relays . Subsonic relay, linestraight relay, MM & MC relays for phono . Since the system has been open for a week now I also found locations of all those relays. They are various places. Fun to know.

HA ! yes somany clicks of relays when you ON the system. but mostly many click together . For now the Speaker SET A is switched OFF and only playing music through the speaker SET B outputs with speakers connected.
I have the A-9 MODEL
 
#39
yes that is true There are lots of those 2291's too . I have seen them on the equalizer board and also on the power amplifier board. But even though I do not have a freeze spray to pinpoint/verify if those transistors could be faulty, I am using my airconditioner to cool the entire system for hours and then run it up to see if really that is the case (thermal heating issue on something). And I know we wouldn't know which one it is when it starts popping . Thats why the freeze spray is more useful .

BUT now I am beating around Speaker relay A set. If it tests positive I will be happy that was the culprit else I will have to buy a freeze spray and check one by one all 5 legged and 3 legged transitors..

Hope it is the speaker relay A set
 
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