Mackie M1400 poweramp problem

[powerampfreak]

Hi all. I had a shorted driver stage (MJE15032/33) in one of the
channels which resulted a lot of open resistors in the output stage,
Some components in the clip-detector circuit blew too. After replacing
all the broken stuff, the channel operates, but with high frequency
ringing superimposed on the fundamental sinewave. Does anyone have a
specific tip for this failure? Some of the compensation capacitors
gone bad? Thanks a lot for any advice!
Regards
Steve

 

[N_Cook]

Hi all. I had a shorted driver stage (MJE15032/33) in one of the
channels which resulted a lot of open resistors in the output stage,
Some components in the clip-detector circuit blew too. After replacing
all the broken stuff, the channel operates, but with high frequency
ringing superimposed on the fundamental sinewave. Does anyone have a
specific tip for this failure? Some of the compensation capacitors
gone bad? Thanks a lot for any advice!
Regards
Steve

Assuming a constant hf then a matter of divining, by literally floating your
hand/finger over, until zeroing in.

 

[gareth magennis]

Hi all. I had a shorted driver stage (MJE15032/33) in one of the
channels which resulted a lot of open resistors in the output stage,
Some components in the clip-detector circuit blew too. After replacing
all the broken stuff, the channel operates, but with high frequency
ringing superimposed on the fundamental sinewave. Does anyone have a
specific tip for this failure? Some of the compensation capacitors
gone bad? Thanks a lot for any advice!
Regards
Steve

Yes, you haven't found all the broken stuff yet. Don't start guessing,
trying to link symptoms with components, you'll be there all day and get
nowhere. Go back and check very carefully all the components from the
output transistors back as far as it is possible for the damage to have
gone.

One technique I use is to use the diode check function on my multimeter,
giving a reading of forward voltage drop. This gives an indication of
resistance and semiconductor junction integrity at the same time. As this
is a stereo amp you can directly compare the working channel with the faulty
one.

Check each transistor junction and all the components using BOTH test lead
polarities, starting from the power devices backwards. (You may be measuring
a base emitter junction with a 100K resistor between the two. In one
direction you will read 100k, the other you will read a 0.6V diode).

Investigate any discrepancies between channels, allowing for changing
readings due to charged/charging capacitors. Both sides should read and
behave the same. This may seem at first to be a very labour intensive
procedure, but with practice can be carried out surprisingly quickly, and
discrepancies easily located.


Gareth.

 

[Eeyore]

Hi all. I had a shorted driver stage (MJE15032/33) in one of the
channels which resulted a lot of open resistors in the output stage,
Some components in the clip-detector circuit blew too. After replacing
all the broken stuff, the channel operates, but with high frequency
ringing superimposed on the fundamental sinewave. Does anyone have a
specific tip for this failure? Some of the compensation capacitors
gone bad? Thanks a lot for any advice!

At all power levels ?

Graham

 

[powerampfreak]

At all power levels ?

Graham

Actually, I run it without the dummy load for initial testings, in
order to operate the amp more safely.. until I get a decent output
signal.
Then I go for power tests.
I think I drove the amp up to somewhere 30-40V rms and the high
frequency oscillation is riding on top of my sinewave test signal.
The OK channel doesn't behave like this, if anyone may think it's just
because I've no dummyload connected.
Besides, there seems to be different version of the M1400, since my
schematic isn't exactly like the amp...
Maybe anyone has a few schematics for this unit in PDF?

Regards
Steve

 

[Eeyore]

Actually, I run it without the dummy load for initial testings, in
order to operate the amp more safely.. until I get a decent output
signal.
Then I go for power tests.
I think I drove the amp up to somewhere 30-40V rms and the high
frequency oscillation is riding on top of my sinewave test signal.

But at lower levels ?

The OK channel doesn't behave like this, if anyone may think it's just
because I've no dummyload connected.
Besides, there seems to be different version of the M1400, since my
schematic isn't exactly like the amp...
Maybe anyone has a few schematics for this unit in PDF?

Ooooh, I did at one time I think. I'll look.

But anyway, do you know what I mean by the 'output zobel network' ? An RC
series combination. The R should be of several watts rating. Do make sure that
the R isn't burnt out (open).

Graham

 

[powerampfreak]

But at lower levels ?


Ooooh, I did at one time I think. I'll look.

But anyway, do you know what I mean by the 'output zobel network' ? An RC
series combination. The R should be of several watts rating. Do make sure that
the R isn't burnt out (open).

Graham- Dölj citerad text -

- Visa citerad text -

The Zobel network is all fine.

 

[Eeyore]

A Zobel network is used for impedance compensation -- usually to make a
circuit look more resistive.

Which it needs to be to counter the effect of the output inductor or you'll
wreck the phase stability of the amplifier.

Graham

 

[Eeyore]

An amp with such a network at its output might very well be unusually
load-sensitive.

Every amp has one prior tot he output inductor.

Graham

 

[Eeyore]

Besides, I can buy a 2000 watt amp brand new also made in China for around
$300 US.

I wouldn't expect it to work for very long.

Graham

 

[Eeyore]

Hi all. I had a shorted driver stage (MJE15032/33) in one of the
channels which resulted a lot of open resistors in the output stage,
Some components in the clip-detector circuit blew too. After replacing
all the broken stuff, the channel operates, but with high frequency
ringing superimposed on the fundamental sinewave. Does anyone have a
specific tip for this failure? Some of the compensation capacitors
gone bad? Thanks a lot for any advice!

http://fileshare.eshop.bg/downloadsm/35996/Mackie_M-1400, M-1400i.html

No schematics though

Here we go
http://www.eserviceinfo.com/downloadsm/27014/Mackie_M1400.html

Graham

 

[Eeyore]

It's the other way around, I believe. The inductor is there for a good
reason.

They both are.

I design power amps btw.

Graham

 

[Eeyore]

I will ask JC about this.

Who is JC and why would his opinion change the facts ?

Grahama

 

[Eeyore]

We've been using one for our 2x18 subs for several months with no problems.

One of my designs has been sitting in the local venue for over TEN YEARS. One
level pot went scratchy in that time and we also gave the heatsinks a
blow-through.

I pulled it apart to have a look and it's as well constructed as any other
amp besides the high dollar brands.

$300 doesn't buy you very much in the way of a power transformer or decent output
devices and heatsinking + fans.

I've heard of these amps in the UK. Not 'Warrior' brand is it ? They came with
ten year warranties but the company only lasted about 18 months. Killed by the
warranty claims.

Graham

 

[Arfa Daily]

I doubt it if as advertised it can "handle 2 ohms all night long".

I wouldn't repair this amp for a "customer" and probably wouldn't waste my
time on it for myself having been burned by Mackie in the past. Besides, I
can buy a 2000 watt amp brand new also made in China for around $300 US.
Someone brought me a used Crown Micro-Tech 1200 they wanted to sell for
$400.00 US and even though I am a big fan of Crown especially that series
I offered half that and they refused. I told them I can get 2000 watts
into 4 ohms bridged for 300 bucks. I used a Micro-Tech 1000 for my bass
guitar rig along with a BBE 383 bass preamp for 10 years worth of regular
club and party gigs without ever a problem. Here's a picture of it along
with 6 and a half feet of other gear I have in a rack.

http://i273.photobucket.com/albums/jj220/meatplow1/music/CIMG0259.jpg

Isn't using a vacuum cleaner as the rack cooling blower, a bit noisy ... ?


Arfa

 

[Tim Phipps]

I wouldn't expect it to work for very long.

Graham

Seems to me that you have a problem with anything made in China. We all
know that you get some crap made there but sometimes some good stuff
comes from there. Most of my amps are British made (Matrix) but I have
a couple of Chinese made amps, one Audiohead and the other T.amp brand
from thomann.de which look like the same amp to me, both have been in
service on the road for about 3 years now without trouble.

You might also remember some time ago when I posted for help with a dead
Studiomaster 700D. The fault turned out to be a bad power transformer
which was not economical to replace even by substitution with off the
shelf parts. That amp got replaced with another Chinese made T.amp from
Thomann which has also given me no problems.

 

[Tim Phipps]

I wouldn't expect it to work for very long.

Graham

Seems to me that you have a problem with anything made in China. We all
know that you get some crap made there but sometimes some good stuff
comes from there. Most of my amps are British made (Matrix) but I have
a couple of Chinese made amps, one Audiohead and the other T.amp brand
from thomann.de which look like the same amp to me, both have been in
service on the road for about 3 years now without trouble.

You might also remember some time ago when I posted for help with a dead
Studiomaster 700D. The fault turned out to be a bad power transformer
which was not economical to replace even by substitution with off the
shelf parts. That amp got replaced with another Chinese made T.amp from
Thomann which has also given me no problems.

 

[James Sweet]

There is a difference between items made in China and designed in China. I
have plenty of Chinese-manufactured items that are of high quality. I have
many fewer that were _designed_ there. One is an iRiver H120 jukebox, which
is of very high quality.

Isn't iRiver Korean? We did some work with their products a while back,
had a couple of their engineers over here, I'm pretty sure they weren't
Chinese but I could be wrong.

 

[Tim Phipps]

Do you remember looking at the 4-63 volt, 3300uf caps in your 700D? I just
replaced the banana jack on mine and those 4 caps looked like the tops
were puffed. I pulled the top off one and there is a convexed steel cap
over the actual can under the heat shrink that makes these look domed. And
they appear also to run pretty warm discoloring the white glue used to
bond them to the pcb. The amp works fine otherwise and I've never had any
problems with it. It was formerly used to power A/V sub-woofers and had
been left on continuously for a couple years. Next trip to the electronics
shop will probably yield a new set just for my piece of mind.

I was beginning to think my posts were not making it out there until I
saw your reply (Arfa was right about the Virgin Media news server being
troublesome!)

I don't remember looking closely but I don't think they were
particularly domed. It was at least 2 years ago when it died. I do
remember that everything looked very clean in there. The amp had an
easy life in a church install but for some reason the power transformer
got shorted on the primary thus blowing the mains fuse every time.
Since it was a custom part I enquired with Toroid International about
purchasing a replacement but it would have cost about £150 as I guess
they were not making these in volume any more. When I saw that I could
just replace the whole amp for the same money it was a no-brainer.

 

[powerampfreak]

One reason I like the 700D is that the cooling system is efficient and the
fan had infinite control. It is as quiet as a mouse until you started to
drive it. It also draws fresh air directly through the front through a
foam cell filter and through a heat sink tunnel and doesn't expose the
entire amp to forced air dust and other contaminates. Mine suffered a fall
while in a rack which broke the A channel banana jack off or I wouldn't
have ever noticed those 4 caps. They're not big enough physically to be
for rail currents so they must serve some other purpose in the driver
stage?? Here is a recent pic of my 700D in the rack that fell over. Lucky
all the other equipment wasn't in the rack when it fell backwards.

http://i273.photobucket.com/albums/jj220/meatplow1/music/CIMG0259.jpg

Below the Crown amp is a rare Sound Code Systems 2350A MOS-FET amp someone
gave me after they couldn't find anyone to repair it back in 1998. It
needed a new set of outputs 2SK134/2SJ49 TO3 case that had been
discontinued and unavailable at the time. I did find a set on the internet
and repaired the amp successfully. It's been used on and off as a source
for 18" subs in a tri-amped band PA setup since then without any problems.
It too is a quiet amp having a similar cooling system to the 700D. It's
heat sink includes a bristled radiator which is unique.- Dölj citerad text -

- Visa citerad text -

The Mackie amp was repaired. A tiny tiny pcb trace/via hole for one of
the predrivers were open circuit.
This happened probably when the drivers shorted. Now everything's
OK!

Regards