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Thread: Rokit 6 g2 repaired ?

  1. #1
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    Angry Rokit 6 g2 repaired ?

    One of my g2 Rokit 6 speakers started to buzz loudly. Fixed the buzz but
    it now has intermittent HF tone at power up.

    Background:

    Rokit 6 g2, playing loudly and all of a sudden started to buzz like hell..

    I powered it down, popped out the amp and connected the HF and LF outputs
    to a dummy load and looked for the source of the buzz. I could see that the
    signal coming from the preamp board looked ok. Voltages looked OK as well.
    however there was this large square wave looking signal on the HF speaker
    output. Took a look at the power supply's for the TDA's.

    I found that the +/- 15V supply had a few bad caps. The 47uf caps on the
    zener references measured a high esr and were low capacitance as was the
    main 100uf cap. on the +15V side. C104 which was supposed to be 100uf/25V
    measured 9uf with an esr of 187 ohms ! The 47uf/35V cap on the zener ref for
    +15 measured 30uf w/esr 40 ohms. I replaced both 100uf/25V caps in the 15V
    supply and the 47uf/35V caps on the zener references.

    I replaced the caps and powered the speaker back on and sure enough
    it was dead quiet. No DC on outputs. Ran a signal through it, could see a
    nice clean waveform on the output, both lf and hf seemed fine.

    Packed it back up and played it for about an hour. Worked find, low vol and
    some pretty high volume to give it a good workout.

    Turned it off, came back about an hour later and when I turned it on I got
    a loud HF tone, not a buzz like before. I turned it on/off a few times. Each
    time the HF tone. wft ?

    Back to the bench. Off comes the back, power it up, works fine ..? I figure it
    could be a connection problem between the boards as some have pointed out
    this is a potential source of issues. I clean and re-seat the connection. Put
    the back on and try it again. Plays great, sounds great for several hours.

    Come back at night, power it on. HF tone again. Back to the bench, remove
    the back and the HF tone stops. I figure it has to be a connection. So I try
    best I can to get it to fail by moving the connector with no luck.

    Thinking cold solder I poke around on the board moving components gently
    but no joy.

    Question is... has someone had a similar issue and found what was causing it ?
    I checked out the Mute circuit, it seems ok. It's almost like something is
    oscillating .. It only seems to happen when the unit has been used for a while
    and turned off for a few hours. If I play it for an hour or so and turn it off and
    back on its fine. I hate the intermittent failure type problems...

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  2. #2
    Old Timer olddawg's Avatar
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    You didn't post a schematic but I have repaired a number of these types of biamped monitors. Generally the first cap that is going to fail and cause a huge buzz is the main power supply filter cap which is the biggest cap in the mess, usually a 4700uf, maybe as low as half that. These caps are usually mounted on a double sided board and buried in glue. You can cause a lot of intermitancies if you don't properly work the double sided boards using the cap leads as feedthroughs. I generally double the voltage rating of the caps if they wil fit.

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    Thanks for the reply...

    The schematic is available on this site. The issue with my speaker was in the tweeter supply. There are two power supplies
    in the Roki 6. A +/- 15 runs the HF tweeter amp and preamp. This is where my problem was. I did check the large
    caps in the +/- 20 V supply. They measured fine. Lucky for me there wasn't much black goop anywhere on my board.
    The bad caps that caused the original buzz in my case were all in the +/- 15v supply. The speaker worked, but every
    few power cycles would have this high-freq tone and when I opened it back up it would stop.

    After cleaning and re-seating the connector between the pre-amp and power-amp sections, I'm happy to say I have had no issues
    (so far ) The speaker is dead quiet and works fine after about 10-15 power cycles and usage over the last few days.

    Click image for larger version. 

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    Quote Originally Posted by olddawg View Post
    You didn't post a schematic but I have repaired a number of these types of biamped monitors. Generally the first cap that is going to fail and cause a huge buzz is the main power supply filter cap which is the biggest cap in the mess, usually a 4700uf, maybe as low as half that. These caps are usually mounted on a double sided board and buried in glue. You can cause a lot of intermitancies if you don't properly work the double sided boards using the cap leads as feedthroughs. I generally double the voltage rating of the caps if they wil fit.

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    Fistly remve all of the black glue on the boards. As much as you can. It can become conductive. It usually does.

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    Stray Cap DrGonz78's Avatar
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    Old thread but just saw a video on YouTube about this very issue that diydidi mentions. Horrible black goop that becomes conductive!! ugh!!

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    When the going gets weird... The weird turn pro!

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    Supporting Member Jazz P Bass's Avatar
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    Ahh, the conductive 'Black Goop From Hell'.

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    Supporting Member The Dude's Avatar
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    I love the guy's disgust. "It's horrible stuff...... I don't like it."

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    “Yeah, well, you know, that’s just, like, your opinion, man.”

  8. #8
    Supporting Member Jazz P Bass's Avatar
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    The engineers probably spec'd one thing and the off shore manufacturer had a brother in law that had a similar product but 'oh so much cheapa'.

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  9. #9
    Supporting Member Jazz P Bass's Avatar
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    Dave is great!

    I love the one where he gets a low frame rate camera and can't decide what to do with it.

    "I know! Let's blow some shit up!".
    https://www.youtube.com/watch?v=9jDsNe_bmtE

    I'll bet he caught grief about all of the shrapnel on the deck.

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  10. #10
    Supporting Member The Dude's Avatar
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    Looks like fun..... blowing up caps. I worked at a pro audio store in the early nineties. They also had a couple bays for installing car stereos. We used to hook up the old car speakers to a variac to see what they'd take. Fun, but smelly.

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    “Yeah, well, you know, that’s just, like, your opinion, man.”

  11. #11
    Supporting Member The Dude's Avatar
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    Since we're already , another fun thing to do is put a CD in the microwave with all the lights in the room off. It looks like a little lightning storm. Probably not good for the microwave, but I haven't hurt anything yet.

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    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    3 seconds and pull it out, you can actually make some interesting art that way... And the microwave will make everyone's lunch smell like plastic for ever and ever and ever and ever...

    Justin

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    "... If an older Boogie and classic Marshall had a (clearly illegitimate) child and you baked it in an oven set to clown shit crazy." - Chuck H. -
    "When receiving a shock I emit a strange loud high pitched girlish squeak." - Alex R -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

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