Im going OPEN-UP a Pioneer VSX-35TX I dont want to BLOW-UP

Discussion in 'The Projects Forum' started by bigcape, Sep 25, 2009.

  1. bigcape

    Thread Starter Member

    Sep 18, 2009
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    Well here goes a real attempt fix something.

    If you don't know, I am getting my feet wet so.... I need simple translated responses please.


    The volume control quit controlling, so my guess is I have to remove and test that POT, right? Right.

    (When I turn the VOLUME control it has very erratic beavior ie: super loud to real soft with no smoothness.)

    I have been reading how caps need to be bled off first,

    My questions are:

    1. Which one? There are MANY!

    2. How? hook up a LED until to all of them til the LED goes dark?

    3. If PCB's run on 5-12V circuits then how the heck to you get electricuted in the first place from a capacitor? Its kinda like a battery storing DC current right?

    Thanks all!

    Ps I just downloade the service schematic HOLY COW!!!!!! WAYYYYYYYYYYYYYY over my head!
     
    Last edited: Oct 14, 2009
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    For an audio amplifier, just leave it unplugged for about an hour with the power switch on. The caps should actually be drained within a couple of minutes, but leave extra time for safety.

    Use a multimeter to measure across capacitors, set to the highest voltage setting.
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    The main risk of electrocution comes from contact with any exposed live mains lead wires inside the box. That's why you would remove the unit's power plug from the wall outlet before taking the covers off.

    As far as problems with capacitors with painful / dangerous voltage levels on them - these would generally be on any switch-mode power supply module which converts the mains level AC voltages to the low voltage DC levels for the circuit boards. These are often marked as being a potential risk to the unwary person who looks inside with the mains turned on or just recently turned off. Also if a capacitor has a marking consistent with high voltage duty - say 250V for instance - one would expect these to be the risky ones. Normally these capacitors discharge a short time after the mains supply to the unit is switched off and disconnected from the outlet. They would hopefully have bleed resistors (or a discharge path) connected across them to ensure they are discharged after a suitable time - say 1-5 minutes at most. Still there is always the chance there is a poorly designed supply which has capacitors which aren't intentionally (or naturally) discharged for safety. The only way to safely assess the situation is to use a multi-meter to check for residual voltage.

    Regarding capacitors on a the low voltage DC side - these would normally discharge shortly after the mains is disconnected. And you are correct - these would not normally be charged to dangerous levels. Again one might encounter a high voltage component even on a predominantly low voltage supplied circuit board. Your "friend" here would be a full circuit diagram for the unit.

    Just to re-iterate an obvious point - disconnect the unit from the mains outlet before you take the covers off. Then wait a few minutes .... and keep one hand behind your back
     
  4. bigcape

    Thread Starter Member

    Sep 18, 2009
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    Since ones heart is on the left side of the body. I choose my left hand!


    Yes of course- unplugged from mains.

    I did as you said left the unit power swich on, but as soon as I unplug from mains power I hear a "CLICK". That would be a relay?

    the repair manual is 117 pages of schematics 9MB file... WOW!

    How did they get anything to work!
     
  5. bigcape

    Thread Starter Member

    Sep 18, 2009
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    Wish this beginner luck! Im going in "nurse, phillips screw-driver please"

    If im lucky I will get to use my new Hakko FX951 for something other than the practicing I have been doing with it on blown transistors!

    (I blew 'em up-- they POP like popcorn! They don't taste as good either)
     
    Last edited: Sep 25, 2009
  6. bigcape

    Thread Starter Member

    Sep 18, 2009
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    Im going to meter all kinds of stuff! Im also going to see if I can figure out some of the 117 page schematic I downloaded. (self teaching experience)

    My FIRST project: http://forum.allaboutcircuits.com/showthread.php?t=27943 did not go so well.


    This will be my 2nd project attempt


    I mentioned a headache in one of my other posts and asprin was reccomended------ so i am going to take one now in advance
     
    Last edited: Sep 26, 2009
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
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    I am in the field of professional repairing, & I would love to guide you
    I do have years of hands on experience when it comes to power amps, I even build them from junks.
    I can definitely help you to get it fixed, but I am truly sorry to say that I won't be available for a week or so. I am preparing to move to another house and to get my ADSL to the new home will take a week or so and I cannot get online.

    This is why I am away for some time since I am involved in renovating the house.

    If I give you an advice to get you starting, you will be expecting me to be here, and I will too. But due to the above mentioned reasons you might not see me, and I don't want anybody to think that I abandoned them when they needed me.

    I might be here for 2 or 3 days, so i will be monitoring this thread.
    If you get stuck, let me know.
    you won't regret it, this I promise'

    Rifaa
     
  8. bigcape

    Thread Starter Member

    Sep 18, 2009
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    Very kind thank you

    No expectations here! Any is appreciated. Congrats on the house!

    I am stuck: check this out for me please please please http://forum.allaboutcircuits.com/sh...ad.php?t=27943

    Rifaa
    [/QUOTE]
     
  9. bigcape

    Thread Starter Member

    Sep 18, 2009
    158
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    UPDATE:

    Help trouble-shoot anyone? The yellow boxes are my questions and notes

    [​IMG]

    IMPORTANT: They call it a "relay" (part #S7101) not a variable resistor! It looks like a pot, has 3 legs, and turns smoothe (no clicks) and when you turn it is has NO BEGINNING and NO END!

    I own 3 other Pioneers and they operate the same.

    By the way, the symptom is when I went to adjust the volume the actual sound would not respond linear.


    [​IMG]
    .
    [​IMG]
    .

    .

    .
     
    Last edited: Oct 15, 2009
  10. flat5

    Active Member

    Nov 13, 2008
    403
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    I can't read the text on your pics. Too small.
    From the trouble you described in the first post, I'd start by cleaning the volume control. There are spray cans for this.
    Also check that the solder connections to the control are good. The "pot" itself does not look impressive and you may want to replace it.
     
  11. bigcape

    Thread Starter Member

    Sep 18, 2009
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    0
    Sorry, I just replaced them in my previous posting.
     
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Hey there, let's see now.
    Before addressing to ur second q? Let's see what we up against.

    First of let me down load the service manual.

    Well obviously you how to take it apart, IC that you taken the Vol Assy.

    I am studying the schema, now tell me what do you have to work, like
    DMM with AC DC and diode check
    Soldering iron and experience.

    I'll get back to you after a I study the volume control method since you said it does not limit in any direction.

    Rifaa


     
    Last edited: Oct 5, 2009
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    This is one fine piece you have here.
    My study revealed that the master volume is not a standard pot.
    This thing is home theater and has around 5 amplifiers, which means a single volume pot states that it is a just a temporary on of switches. It does have any limit to the end, it can be rotated cont. meaning a digital Volume control.

    Take a look at the service diagram, referring to what I have, page is 37, find the box labeled T Volume cont assy (AWX577), in it in the right below Is the master volume S7107. You can Clearly see two switches.

    Taking what you said about volume jump, it could be a dirty copper tracks inside the Volume control.
    This type does not use carbon, but has one round copper tracks and the outer copper has increments, the shaft has the leaf contacts, when rotated the contacts produce pulses depending on the direction of rotation.

    Now since you taken the volume assy, I suggest you carefully take the volume apart, you have to desolder it to get a thorouogh cleaning, Just use a very fine sand paper, don't use anything abrasive and clean the copper tracks carefully and also the leaf contacts.
    Now use a little alcohol to clear the stubborn grease from the shaft to get a smooth rotation ( use a mild grease to lubricate the shaft ).
    Be carful with the leaf contacts, it is delicate. don't amply too much presssure on the leaf contacts. A little to and fro movement will clean them.

    Now put it back on and test the amp. Check the cables for firm connection.

    If this does not help, post back.
    No worries.

    Rifaa

     
  14. bigcape

    Thread Starter Member

    Sep 18, 2009
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    Very kind very kind! thank you
    That was the easy part!
    Everything listed but the experience!
    That is a fact- no limit. It turns like a knob on a Lexus automoblile. Almost has a "fluid filled" feel to it.

    Rifaa
     
  15. bigcape

    Thread Starter Member

    Sep 18, 2009
    158
    0

    Thank you, thought it was worth a try to fix it.

    I thought so too!

    Thats why it has no limit, I guess? It couldn't be an easy one for my first "real" project!


    Have you looked at pages 68,71,76,90,94 and 95 as well? Is there anything there interesting? (I wouldn't be able to tell)?

    Do the pulses come from the black stripes?

    There is a problem: There is the non-conductive lube that is VERY THICK
    If I get it all out of there I do not know what to replace it with!! ??

    I can tell it is supposed to be THICK for reason but I do not think it is supposed to be "LUMPY"

    YOU ARE LOOKING AT A 14X MAGNIFICATION

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    What kind?

    You are soooo right!

    I'm not gonna do anything yet t'ill you've seen the photo's! Oh "Wise One"

    I have my own diagnosis: (I mean GUESS of course)

    1. I tested the gooey stuff:
    a. non conductive
    b. looks like heat stress (viscosity breakdown)
    c. shouldnt be "lumpy" ?

    2. Replace the gooey lumpy stuff:
    a. with new gooey NON-lumpy stuff!
    b. test somehow before reassemble?

    3. Bragging rights if it works

    4. Don't tell anybody if it doesn't so friends don't
    think I've "lost-it"

    Can this component be tested? I mean with what I have to test? I sure hate to have to assemble just to end up taking back apart!
     
    Last edited: Oct 15, 2009
  16. meorbu

    New Member

    Oct 6, 2009
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    0
    you need oscilloscope to test it, do you have it?..
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Oh ! how I wish every one would post like you. Nice indeed.

    Taking a look at those pics, the gooey stuff means the grease is used up, clean the whole thing with spirit or any mild alcohol that does not harm plastic.
    Then you have to find grease which are used to lubricate DVD or VCD mechanisms, I think you can find if you visit ur electronic stores. Just ask for grease used to lubricate the laser pickup shaft. It's a very light grease.

    The shaft rotation should will be very light to the touch.

    Looking back to the pics, i don't see enuf oxidization that could prohibit it from properly working but looking at the outer ring, there is little oxidization.
    (the tracks are reversed, with the ring at the out side and the increments on the inside )
    Clean all the metal parts till they shine like silver, again don't use any thing abbrasive.

    Lift the leaf contacts a little to compensate of the years of use, it has a spring effect so that the leaf touhes the tracks firmly.

    If the leafs are properly aligned assuming yuo did not bend it side ways, you can asemble it, put every thing back as it was in to the amp, and test it.
    From there we will proceed.

    Rifaa


     
    Last edited: Oct 6, 2009
  18. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    If the volume is not OK after this, then the rotary encoder is not the culprit.
    To test it you have put every thing back and power on the amp.

    A digital voltmeter can be used to test if the encoder works.

    I'll tell later if the cleaning fails, how to measure voltages at the appropriate points.

    Rifaa
     
  19. flat5

    Active Member

    Nov 13, 2008
    403
    17
    This particular volume control is just a fancy switch.
    You can test it with an ohm meter.
    You can buy a digital multimeter for $5 or less.
    Sometimes you can find an analog volt/ohm meter for $5 or less.
    Good luck with this project.
     
  20. bigcape

    Thread Starter Member

    Sep 18, 2009
    158
    0
    I havent justified the expense at this point in my hobby carrer!
     
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