Left speakers dont work unless hit

Discussion in 'General Electronics Chat' started by JJS1234, May 26, 2011.

  1. JJS1234

    Thread Starter Member

    May 26, 2011
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    Hello everyone, my title is a little vague. Im not sure how to describe the problem really.

    I have an older Sony Stereo/Receiver that was built in the 1990s (early) and lately (or rather for awhile now; I haven't used it that much) the left speaker doesn't transmit sound (the right side does however and is fine) unless I:

    -Hit the top of the receiver with my hand,

    -Turn up the volume to 3/4 max and then their is a popping noise and then it works.

    The other thing is the left speaker may stop working after awile of trouble free operation.

    I was talking to tech about it and he mentioned something but I cant remember what it was, so I am asking here.

    I kinda wonder if its one of the Power Relays (if thats what they are- I hear a TICK right after I turn the power on and off- its shaped like a blue or black box).

    Anyway I just need an idea on what it might be since parts are really cheap and I dont mind soldering either. :D

    PS: Model is: SONY STR AV1070x.

    Thanks for any help!


    By the way, if this is in the wrong forum you can move it- I just thought since the topic is radio and comm. that it would be alright.
     
    Last edited: May 27, 2011
  2. KJ6EAD

    Senior Member

    Apr 30, 2011
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    You're on the right track. I had a Sony of that era and it had bad load relays (output to speakers). Reflow the solder on the relays with some flux. If it's still bad, replace the relay. You may have to find a compatible but different relay.
     
  3. JJS1234

    Thread Starter Member

    May 26, 2011
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    Yeah I just wrote down the part numbers for them.

    I have a couple questions for you and the relay pros:p out there:


    -Can one relay control 2 different channels for speakers? (its a 2 channel stereo) or would their have to be 2 relays and one is bad? The one I suspect is in the motherboard. Its a 24v DC/7A/250v AC Relay.

    -If I cant find the exact relay (the one i have is a Six prong) can I use a 4 prong and somehow jerry-rig it--- OR--- would it matter if say I found one but it was 10A instead of 7A?

    And of course if I do find one does it matter which way it plugs in?



    I believe I have 6 relays: 1 is for powering on the system, their are 2 in the motherboard (the one I listed is like 3x bigger) I know one is for an Auxiliary system (because you can hear it when I press one of the aux buttons on the front panel), and 3 smaller ones are on a small external card that does have connections to the back speakers (ALTHOUGH I believe it is just the front- I will test this theory) and may have connections to the front.

    However now that I read what I wrote I believe it could be one of the rear 3.

    I will have to see what Fry's has in stock tomorrow (if they have all) and buy them all.
     
  4. KJ6EAD

    Senior Member

    Apr 30, 2011
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    What? I only care about the part that doesn't work. Could we identify and talk about that?

    Turn the unit on with the cover off. If it's got the dead left channel, push down lightly on each suspect relay with an insulated tool (a small stick will do). If you press on the bad relay and the left channel suddenly works, you've found a badly soldered relay. If that doesn't get it, try tapping on them one at a time. This simulates your banging on the case but makes the mechanical shock relay specific.
     
    Last edited: May 27, 2011
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  5. JJS1234

    Thread Starter Member

    May 26, 2011
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    Im not sure which one out of the 6 works or not, let alone how to tell.

    Ive taken a close look at all of them and I can reasonably say the the solder is on there well, its connected.
     
  6. JJS1234

    Thread Starter Member

    May 26, 2011
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    Started doing what you said. It seems to be around that relay- just pushing lightly (like literally a leaf could do it) their are 2 fairly large capacitors right next to it- and it does the same when I push lightly on them. I think when the board is bent slightly it does it. I will re-solider all connections in that area.

    Thank god for the De-soldering wire I got with the solider kit.

    Will let you know.:)
     
  7. KJ6EAD

    Senior Member

    Apr 30, 2011
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    It's amazing how many circuit faults can be found by careful visual inspection and poking with a stick. :D
     
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  8. JJS1234

    Thread Starter Member

    May 26, 2011
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    Yeah you were right. I just figured it the soldiering was done by a machine so thus its perfect. May be the case but then again- nothing is more powerful than entropy.

    Probably just either that or moving it disturbed it.



    I had a resistor and a transistor replaced, the silicon where they were was a dark brown/black. Had to do a bypass.

    The transistor is pretty small but is extremely hot (Would think upwards of 160+). Any recommendations how to lower the temp?

    I was actually thinking of adding a 12v (120mm or larger) fan and a mini heat sink. Connecting it directly to the transformer. Do you think that would be fine?
     
  9. KJ6EAD

    Senior Member

    Apr 30, 2011
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    The transistor may be the driver for one of the relay coils. It's impossible to say what else is wrong from this distance. One frequent failure mode for devices of that age is power supply filter capacitor leakage due to dried out electrolyte.

    Is it your understanding that the intermittent was caused by the heat damaged PCB, and is that problem solved now?

    I would scrap a piece of consumer electronics before I would add a cooling fan to it.
     
  10. Jotto

    Member

    Apr 1, 2011
    159
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    They make heat sinks for transistors, see if you can get one off a scraped piece of electronics. Pay attention to the area and size of the heat sink, as long as you have a safe distance from other components you will be alright. Some things to get hotter then others, it might be how it was designed to work, but removing some of the heat is good.

    Cold solder joints are a common problem with any electronics when heat or vibration is involved. We had a machine type that would start chattering a solenoid, the frequency it oscillated at would cause a cold solder joint. Power supplies are great for developing cold solder joints.
     
  11. JJS1234

    Thread Starter Member

    May 26, 2011
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    The 2 Large capacitors do have some white gooey looking stuff around them on the base. It almost looks like the consistency of heat transfer liquid you would put between a CPU and heatsink.

    Its on both of the capacitors but only on 1/2 side of them. Is this what you mean by the electrolyte being dried out? The capacitors aren't bulging (but that may be something different).



    I do have a really large heatsink that is already in the stereo. The transistor is about 3" away from it. Do you think I could extend it with some wires and then attach it to the heatsink?
     
  12. KJ6EAD

    Senior Member

    Apr 30, 2011
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    That's probably just some silicone adhesive helping hold them in place.
     
  13. JJS1234

    Thread Starter Member

    May 26, 2011
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    Thanks KJ6EAD and Jotto. Got everything fixed. The only thing I wish I could do is get a 12v computer fan to run, but I dont think I can do that without a transformer right? The voltages observed are 5v-25v-50v-120v-500v. Maybe a 25v (Pretty sure 25v comes out of the HUGE transformer is DC) to 12v?
     
  14. tom66

    Senior Member

    May 9, 2009
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    Those are just cap voltage ratings, the voltage across them may be much lower. The 25V one probably has 12V or 15V across it. 15V will run a computer fan but it will run faster than usual and have a shorter lifespan as it will get warmer.
     
  15. JJS1234

    Thread Starter Member

    May 26, 2011
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    Hmm. Do you think their would be any way to say make my own 120v to 12v power supply that is smaller than one I would see in a computer? I would only need to run say 2 fans with the total Amps at 2 also.

    I was thinking to hook it up to the 120v relay so that when the power is triggered on the stereo- then the fans would come on.

    But I was reading the diagram for the stereo (alot of signs I dont understand) and it maybe that the power from the wall (120v) goes directly to a transformer that ups it to 500v and then goes to a HUGE transformer 6" by 6" and that turns it down to the different voltages. But I have no clue its all speculation.

    Do you have any books that are recommended that I could read to better understand the signs?
     
  16. KJ6EAD

    Senior Member

    Apr 30, 2011
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  17. tom66

    Senior Member

    May 9, 2009
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    Hmm, I wouldn't expect 500V in an amplifier unless it was a really high power amplifier (i.e. for concerts etc.)

    You could bypass the 120V - 12V solution by buying a cheap fan which works on 120V. Here is one about the size of a computer fan - 12cm x 12cm. Remember, 120V is mains voltage. It can kill. Be very careful.

    http://www.rapidonline.com/Electric...x-Fans/120mm-Low-noise-mains-axial-fans/70817

    Note, that one is 230Vac but it should be easy enough to find a 120Vac fan.
     
  18. JJS1234

    Thread Starter Member

    May 26, 2011
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    I didn't even realize but their are plugs on the back of the stereo. The plug says 120v 1A max which isnt very much. The plugs turn on and off when the main power is turned on/off with the stereo.

    I just cut some leads off of a transformer and plugged it in. It says 12v .5a. And my question is how many amps is the transformer drawing in 120v? Could I plug another fan in is what I am trying to say I guess :p.

    I know that amps decrease with voltage increase, just not sure how much.
     
  19. tom66

    Senior Member

    May 9, 2009
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    Assuming a 100% efficient transformer it is 0.05A, because the output voltage is divided by 10. Energy (and, over time, power) must be conserved. 12V * 0.5A = 6W; 120V * 0.05A = 6W. Now in reality, it will draw a tiny bit extra due to losses and such, but they are almost negligible.

    Be careful to remember that a 12V transformer only puts out 12V when it is loaded with its rated load, in other words, 0.5A. I've seen 18V outputs from 12V transformers! The fan is unlikely to be damaged by this but it will run faster. So it could be prudent to insert a resistor of some kind - maybe around 10-20 ohms - in series with the fan - to slow it down. After all you don't want the fan to overpower the audio.

    Also make sure the output is rated at 12VDC not 12VAC!
     
  20. JJS1234

    Thread Starter Member

    May 26, 2011
    41
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    Sweet. I wasn't sure I could connect my 2 tape deck with it. But it looks like I will be able to and possibly a dvd player aswell (the dual tape deck only draws some 40 watts). I was able to get 3 fans in their 2 80mm and 1 30mm ish. One of the fans is loud but it doesn't matter really since the speakers will always be louder.
     
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