powered speakers amp problem

Discussion in 'Technical Repair' started by dougalere, Sep 1, 2016.

  1. dougalere

    Thread Starter Member

    Mar 4, 2015
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    upload_2016-9-1_11-55-11.png
    upload_2016-9-1_11-57-27.png

    amp problem
    having problems getting my camera to focus, best i can do at the moment.
    re lower pic -plenty of manufacturers black gunge which apparantly can become conductive.
    tried removing it but its solid like fibreglass resin.
    bit of a mess, ill have another go at cleaning it up later.
    going to power it up later and provide some info.
    on the top pic have replaced some obviously damaged componants resulting from damp./condensation.
     
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  2. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    just powered up, working on the HF TDA2052 first, getting a slight pop from the speaker on power up. ,but no audio,(cd player source)
    plenty of voltage on the mute pin ,
    using the same preamp board as before so we know thats ok.
    if i touch the amp chip pins i can hear it in the speaker,
    the chip was getting hot but has no heatsink (removed for access)

    im pretty sure the LF amp will be the same ,. no audio,
    but i need to resolder the LF speaker wires back on first.
     
  3. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    i should add that prior to being powered off and put away for a few weeks, i was getting full audio, albeit taking over 5 minutes to burst into life,after being powered off overnight.

    could be something thats common to both amps.?
     
    Last edited: Sep 1, 2016
  4. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
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    ive checked continuity from HF on the preamp to pin 7 on the audio chip through ch100.-thats ok. so the chip should be getting audio.

    cant test ch100 though.
     
  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    The input circuitry is common, power supplies are common.

    Take a 10 if capacitor. On an audio cable, take the hot side to one lead of the capacitor. Ground the audio ground at the 1 point ground. The other lead of the capacitor becomes your probe to inject a signal at various inputs to see where you have sound and where you don't. You can use the half split method to speed up your search.
     
  6. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    upload_2016-9-1_18-9-13.png
    thi is my meter, purchased from a company called maplin, probably rebadged, looks as thats ready for a clean,
    here in the uk we have a saying the camera adds 10lbs,. i think it shows up a lot of muck, as well ,
    im going to have to give it a clean,

    on my photos in windows picture and fax viewer i have infinite zoom,. would it be better to send board pics
    as an attachment?rather than copy and paste.
    half split method ?

    joe what would i expect to hear ?
    1 point ground.= i havent found that can i use signal ground,
    wait- ive just spotted a mains? ground screw on the backplate,


    re probe- it would be handy to have a spare pair of dmm leads, .i'll see if ive got a couple of big sewing needles.
     
    Last edited: Sep 1, 2016
  7. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    upload_2016-9-1_18-57-43.png
    re probe-it would be handy to have a spare pair of dmm leads
    thats easily solved, the tube from an amp connector is a perfect fit to the dmm plug .
     
  8. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    upload_2016-9-1_19-28-23.png
    thats a bit worrying, just checked on that dil chip on the main output amp board next to the input multiplug...
    dont think its on the schematic.
     
  9. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    well theres 6 dual op amps on the preamp board = 12 op amps,
    there is 14 op amps on the schematic, so partially solved, i say partially because i dont know which 4 op amps on the schematic are on the quad.chip.
    limit?
     
    Last edited: Sep 1, 2016
  10. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Whatever music you have playing from the music source.



    Page 18 of the diagram, just to the left of the VDD supplies is the 1 point ground. This is typically used to prevent ground loop hum and other noise.

    Look at diagram on page 16. The half split method allows you to inject or measure a signal at the mid point. If using signal injection, and you hear the output from the speakers, the problem is before your point. If you were using an oscilloscope, and you saw a good audio signal at the mid point, your problem is after that point. It's like guessing a number from 1 to 100. In old TI programmable calculators it was called a hi/lo game. you choose the mid point and based on the response, you move half way up or down until you solve number. The same is used in troubleshooting, but you need to know the overall system.

    On page 16, where you see the limit tag between UP2A and UP2B is the last point where the signals split into HF and LF. If you hear sound from both speakers there, you move left on the schematic to another point to inject a signal. Work your way till you hear a signal.

    I see your DMM is a M135 ... but your meter leads are covering some other information that could be useful. I'm thinking it's probably a 10 Mohm input impedance, but I wanted to be sure.
     
  11. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Here is PCB1 foil side. I left some comments on the picture.
     
  12. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    joe
    just checking out that quad pending your advice, thank you,
    as it is a fault thats common to both amps the quad circuits could be worth a look..that area looks good though'
    its comment deleted.. the first 3 sections of the preamp -up1a,up1b and up2a are on the output amp board( .the quad chip.)and then returned to the preamp board,
     
    Last edited: Sep 1, 2016
  13. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    upload_2016-9-2_4-0-35.png
    i think this is the board that goes with the schematic, that quad is missing and it shows the limit relay.
    will get the probe working in the morning,
     
  14. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
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    upload_2016-9-2_10-20-51.png
    SO THE SIGNAL PATH IS SOMETHING LIKE THIS?.
    tricky to trace, bt also means very low level audio right next to power componants.
    should of course be another 2 lines lf and hf from the multiplug to the output amp oops

    re drawing-i know i was in a rush.

    re your pic of the copper side- that central area was the worst affected by damp/corrosion
    and is the mute circuit-.hence being suspect in previous thread,but it seems to be ok,
     
    Last edited: Sep 2, 2016
  15. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    In your attempts to clean it, you could have fractured a connection or pushed leads down, shorting to other soldered pads. If your satisfied the areas I questioned are ok ... That's good.

    Half splitting is just one technique. Signal injection is your best option unless you have an oscilloscope. For analog audio work, a 50MHz scope is fine and probably inexpensive.
     
  16. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Looking at that picture of the connector, you should be able to measure audio at the sing out pin, and it comes back at the H and L pins.

    I suspect it would be a low level audio in the hundreds of mV AC.
     
    Last edited: Sep 2, 2016
  17. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    hi joe
    bad news,i tried the probe in numerous places but couldnt get anything,nothing on the multi plug
    i dont think theres a limit circuit on this-
    that must be on later versions..but i did find the that point .
    although i was very careful not to bridge anything, ive lost all power,i suppose thats the problem when there is power and signal componants mixed up together.
    i was probing around dh100 and rh106 i think .
    ,time for a break
     
    Last edited: Sep 2, 2016
  18. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    You aren't the first, nor the last, to accidentally short a power supply. Enjoy your break.
     
  19. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
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    good to know your still there joe..
    if the worst comes to the worst, hes got one good speaker cab, we had more or less written them off anyway.
    he could buy a complete replacement assembly for around 85 gbp-.thats everything apart from the cab and cones.

    i might not be entirely to blame, while i was having a quick cuppa,i heard some loud crackling from the speaker, and the audio chip was red hot . that was just before it lost power',could have had a bit of thermal runaway,

    i dont think it will be to bad to sort out, hope its not those transistors.....
    as always your opinion valued, shame about the different time zones.
    found the main ground at the neg of c100, couldnt miss it really.
    im a bit puzzled as to how the cap probe works
    found the limit line much harder to trace,
    the missing limit circuit is still a mystery.

    all the op amps are numbered on the board apart from the quad chip. so ill do a more detailed layout.
    its a shame part of the preamp is on the main board, i could have knocked a new board up in an hour.
     
    Last edited: Sep 2, 2016
  20. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    looks as though i might Have been a bit hasty,
    definately got power.
    voltage on the hf chip +VS 21 VOLT -VS 21 VOLT a bit high ? relative to power ground.
    no audio at all
    looks like i was right about the chip going into
    meltdown,and of course its the only expensive thing on the board.

    ill connect up the LF chip in the morning,
     
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