Subwoofer problem Mackie swa 1801

[ri23c]

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.

[ri23c]

Some idea?

[g1]

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:
http://music-electronics-forum.com/t35220/

[ri23c]

Thanks'll take a look and let you know

[ri23c]

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.

[ri23c]

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.

[ri23c]

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

[ri23c]

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

[ri23c]

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.

[ri23c]

Some idea?

[Jazz P Bass]

The translation to English is not going well.

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

[ri23c]

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

[ri23c]

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?

[ri23c]

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.

[skipp025]

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