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Science Forum Index » Electronics - Repair Forum » Mackie M1400 poweramp problem...
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| powerampfreak... |
 Posted: Tue Jun 03, 2008 11:24 am |
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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 |
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| N_Cook... |
| Posted: Tue Jun 03, 2008 4:38 pm |
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powerampfreak <powerampfreak at (no spam) hotmail.com> wrote in message
news:220a9a3f-1e0e-4ad2-9989-f14d349cafb6 at (no spam) j22g2000hsf.googlegroups.com...
Quote: 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.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/ |
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| gareth magennis... |
| Posted: Tue Jun 03, 2008 5:25 pm |
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"powerampfreak" <powerampfreak at (no spam) hotmail.com> wrote in message
news:220a9a3f-1e0e-4ad2-9989-f14d349cafb6 at (no spam) j22g2000hsf.googlegroups.com...
Quote: 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. |
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| powerampfreak... |
| Posted: Tue Jun 03, 2008 6:27 pm |
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On 4 Juni, 04:07, Eeyore <rabbitsfriendsandrelati... at (no spam) hotmail.com>
wrote:
Quote: powerampfreak wrote:
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
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 |
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| Eeyore... |
| Posted: Tue Jun 03, 2008 9:07 pm |
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powerampfreak wrote:
Quote: 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 |
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| William Sommerwerck... |
| Posted: Wed Jun 04, 2008 9:24 pm |
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Quote: Which it needs to be to counter the effect of the output inductor
or you'll wreck the phase stability of the amplifier.
It's the other way around, I believe. The inductor is there for a good
reason. |
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| William Sommerwerck... |
| Posted: Wed Jun 04, 2008 9:24 pm |
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Quote: William Sommerwerck wrote:
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.
I will ask JC about this. |
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| Meat Plow... |
| Posted: Wed Jun 04, 2008 9:33 pm |
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On Thu, 05 Jun 2008 02:12:45 +0100, Eeyore wrote:
Quote:
Meat Plow wrote:
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.
We've been using one for our 2x18 subs for several months with no problems.
I pulled it apart to have a look and it's as well constructed as any other
amp besides the high dollar brands. |
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| Eeyore... |
| Posted: Wed Jun 04, 2008 10:33 pm |
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William Sommerwerck wrote:
Quote: Which it needs to be to counter the effect of the output inductor
or you'll wreck the phase stability of the amplifier.
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 |
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| Eeyore... |
| Posted: Wed Jun 04, 2008 10:34 pm |
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William Sommerwerck wrote:
Quote: William Sommerwerck wrote:
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.
I will ask JC about this.
Who is JC and why would his opinion change the facts ?
Grahama |
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| Eeyore... |
| Posted: Wed Jun 04, 2008 10:38 pm |
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Meat Plow wrote:
Quote: Eeyore wrote:
Meat Plow wrote:
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.
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.
Quote: 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 |
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| Tim Phipps... |
| Posted: Fri Jun 06, 2008 10:08 am |
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Eeyore wrote:
Quote:
Meat Plow wrote:
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
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
replace "invalid" with "uk" to reply by email |
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| Tim Phipps... |
| Posted: Fri Jun 06, 2008 3:07 pm |
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Eeyore wrote:
Quote:
Meat Plow wrote:
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
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
replace "invalid" with "uk" to reply by email |
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| William Sommerwerck... |
| Posted: Fri Jun 06, 2008 7:52 pm |
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Quote: 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.
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. |
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| Meat Plow... |
| Posted: Fri Jun 06, 2008 10:26 pm |
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On Fri, 06 Jun 2008 16:08:03 +0100, Tim Phipps wrote:
Quote: Eeyore wrote:
Meat Plow wrote:
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
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.
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. |
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