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Thread: Subwoofer problem Mackie swa 1801

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    Subwoofer problem Mackie swa 1801

    Hello everyone, I have a problem with the active subwoofer Mackie swa1801. The problem is this: I turned on the sub that for many months, and I turned on not raising the volume from my phone lights up the led thermal. Viewing manual means that the temperature exceeds 60 degrees, and should also go mute but feels the same but I had just turned on. I disassembled the amplifier and I noticed first by the smell of something hot and then I had confirmed with my finger that I burned by touching the resistance r65.Prima I became aware of the resistance I raised the pot that's on panel and (do not know why I did it), the red led is lit thermal altogether and burned the transistor q12 . the transformer is not original because I took the sub used and that the former owner had changed with a more powerful (if you do not know what he meant with more tension hope not or higher amperage) because it was burned. Before I realized the problem I noticed a sound distortion. What could it be?
    Sorry if the text is not particularly spelled it right because I'm Italian and I do not know much English.

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    Supporting Member Jazz P Bass's Avatar
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    It sounds to me like U3 is faulty.

    Agilent (Hewlett-Packard) - datasheet pdf

    And possibly also Q14.

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    Thank when I changed them and tried do you know

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    The components that take new must be the same brand of those mounted or can be of different brand?

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    Supporting Member Jazz P Bass's Avatar
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    As long as the datsheet particulars for the original component are met, 'brand' does not matter.

    To be sure, Iwould replace both U1 & U3 & the power mosfets Q6 & Q14.
    Also. seeing that Q12 took a hit, it may be wise to aqlso replace Q9.

    Mackie_SWA1801_Amp_sch.zip

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    I'll let you know.

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    I noticed that the mosfet q6 & q14 are mounted IRF540N, but the schema is written IRF540. it is better to take the mosfet that holds more amps or the original as in the diagram?

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    Looking at the datasheet I've seen that the MOSFET mounted on the board that is IRF540N has Rds (on) of 44mΩ rather than schema is Rds (on) of 0.077Ω. Which mosfet use ??

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    Supporting Member Jazz P Bass's Avatar
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    I would go with the IRF540N.

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    OK thanks
    I also noticed that the c2 & c capacitors 34 are mounted on schda 100v instead in the scheme are to 63v. I keep those to 100v?

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    Does anyone know the output voltages of the original transformer? And the amperage

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    Removing the card has torn the insulation. I put the insulating mica or silicone?

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    I changed U3, U1, Q6, Q9 and Q14. amplifier wake there is always the R65 resistance that heats more than r1. I noticed a distortion when I turned up the volume before you turn on the LED thermal. I forgot to tell you, that when I disassembled the amplifier from the rest of the subwoofer, I noticed that a transistor (Q5) of the final did not touch the heat sink. It could be the one causing the problem?

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    I solved the problem of transistor q12 that continued to burn. When I turned on the amp I measured the voltage from f1 and f4 fuses which is 35v but drops to 34V when I put the music. I still have the problem of the thermal LED that lights up when I exceed a certain volume of sole and r65 resistance warms much more than r1. What can be, I checked all the transistors and diodes on the board and they are all good. It could be u3?

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    Tell us what the issue was with Q12, maybe it will serve as a clue.
    Certified Dotard

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    Which was one of two copper tracks that start at q12 and arrive at pins 1 and 2 of u3 had been damaged insulation and was short on the heat sink.

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    Some idea?

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    Have you checked the zeners D3, D30, D2, D38 ?
    Does R1 get hot? It should. If not, maybe the problem is related to R1 and R65 is hot like it should be?
    There is lots of info. in this thread:
    Mackie SWA 1801 Service Notes
    Certified Dotard

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    Thanks'll take a look and let you know

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    The diodes are good and d38 I had already changed because I noticed that next to the resistance r65 was a little blackened, perhaps for warmth.

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    R1 is warm but not as r65
    I tested the diode d30 and gives me 0.419v with the red lead to the anode and the black on the cathode. Reversing the test leads 0.917v me, and gives me the same results even d11. Dismounted from the d30 card gives me 0.416v but reversing the test leads from 0v, so it is good as well as d11.

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    I found a short between the q6 drain and the mass but only if I put the red lead of the tester to the drain and grounding black. What can it be? The mosfet is new

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    He also gave short between the drain and the drain of the q6 q14, but not anymore.

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    I turned on the amp and I measured the voltages and they are: on pin 1 and 2 u1 me 0.428v and on pins 1 and 2 of u3 me 0.437v. Increasing the volume tensions on pin 1 and 2 of u1 and u3 rise. I measured the voltage from the bridge of diodes d40 and 17.21v measuring the positive and ground and -17.16v between negative and ground. I noticed that go down a little when I raise the volume. I realized that if you increase the volume from the potentiometer on the amplifier panel and turn up the volume of the thermal LED does not light but feels the distortion. It may be the board input to cause distortion and the problem of thermal led? When you hear the distortion voltage (measured between the positive / negative and ground) it is about 15.80v.

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    Some idea?

  26. #26
    Supporting Member Jazz P Bass's Avatar
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    The translation to English is not going well.

    What seems to be the specific problem at this point in time?

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    Sorry for the translation
    I tried the board input with another amplifier and not by problems now try to change u2 and let you know.
    Sorry again for the translation

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    I changed u2 and would not light up the LED thermarl. I still have the distortion. I measured the voltage u1 and u3 and always remains at 18v to 17v with no music while sciende when there is music. I measured the voltage on pins 1 and 2 of u1 and u3 and I see that rises to about 1.4v. I think because it distorts not enough tension, in your opinion?

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    I think I found the problem. I measured the voltage on the zener diode d38 and is of 16.14v and drops to approximately 16 volts. I have the same problem even on d2.

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    Trouble Shooting the Macke SWA 1801 SubWoofer System

    > Hello everyone, I have a problem with the active SubWoofer Mackie SWA 1801.

    Well, here it is July of 2017 and I wanted to contribute some information about
    the SWA-1801. I actually like the design, but the circuit does have some deficiencies,
    one appearing to be lack of reliable output over current protection.

    So a friend bought one used from Craigslist (should have known)... only made only
    a small sizzle sound when he plugged it in and guess who was asked to help out,
    because his guru tube amplifier guy didn't want to deal with it. Since he will use
    the 1801 I offered to help him get it going.

    Physical examination only indicates a few burned resistors, in the voltage amplifier
    "VAS" and output pre-driver stages, something like R8 and R56 come to mind as I
    type this. An examination of the schematic shows they're kind of sacrificial and
    degeneration resistors anyway, so no big deal. With these resistors burned open,
    we would expect to find problems/shorted parts in the mentioned sections... and
    of course we found some of the transistors shorted.

    Of course no good deed goes unpunished, a trip around the rest of the board with
    a decent Fluke Multi-meter found a pretty good number of other transistors, diodes
    and FETs shorted. So a list of replacement parts were ordered and I expect to
    have the amp back on line in another week or so, just need to make time to
    do the deed.

    A caution to some of you back yard techs, be sure to order the correct replacement
    (exact type) parts, many of them are specialized for the circuit... ultra-fast recovery
    diodes, special flame-proof resistors, Toshiba output transistors, that sort of thing.

    In the trouble-shooting mode and the component level, note the power supply
    stacks the high voltage on top of the pre-charging 18 volts through DU10 and
    DU33. The high voltage arrives to the output after a delay and normal volts
    start sequence through/from the HV power supply via fuses F1 and F4. An
    assumption could be made (often incorrect) that a failed amplifier found with
    the fuses blown is a simple replacement fix (replace the fuses). Turns out the
    fuses only potentially protect some possible situations when predictable problems
    occur, as not found in/with my repair situation... you should also be so lucky.

    So the amplifier we have here experienced a host of failed parts, current today's
    part pricing to fix this beast is $200 if you assume you're going to need to replace
    most of the output amplifier, power supply, VAS (section) and output devices.
    But a working version of this unit is worth the parts to fix it, so off we go to
    get that done.

    I'll do a bit of testing and scenario evaluation to determine if normal operation
    would ever offer a potential repeat of this catastrophic failure; and if it's
    more than remotely possible, a few methods of current protection will be added
    to the system. This thing is rated for 800 watts? I'd ask who in the heck would
    want 800 watts of sub-woofer, but knowing this amps owner (Chris), I already
    have the answer.

    Otherwise, if you study electronics including audio amplifiers, the SWA-1801 has
    some really interesting sections of a traditionally otherwise boring transistor audio
    amplifier... but one of the missing portions within the design appears to be serious
    output current limiting protection... so if you abuse it... you'll probably be over
    here reading posts from people who've also had to "open it up" for a fix.


    cheers,

    skipp

    skipp025 at ya who period calm

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    Do you know the voltage of the amplifier? The old owner has changed transformer and I do not know if that is the right one. The mounted transformer is 800VA with +- 90V DC and +- 18V DC. The +-18 V DCs are right because the schematic is written so, but other tensions do not know them.

  32. #32
    Supporting Member Jazz P Bass's Avatar
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    The power supply high tension filter capacitors are rated for 100 Vdc.

    So 90Vdc will work.
    It may be a bit high.

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    Ok thanks, but what is the original voltage of the amplifier?

  34. #34
    Supporting Member Jazz P Bass's Avatar
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    I do not know.

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