Re: HK 930 receiver blows right channel speaker fuse.
- From: maxhifi <no@xxxxxxxx>
- Date: Thu, 01 Nov 2007 05:47:40 GMT
Simpson wrote:
Mark D. Zacharias wrote:
"john jack" <null@xxxxxxxxx> wrote in message
news:jCqVi.3531$Nz7.380@xxxxxxxxxxxxxxxxxxxxxxx
Peter Larsen wrote:
john jack wrote:Without speaker load. I followed the diagnostic procedure spelled out by
I small correction: the right channel was about 135 mv and the leftwith or without speaker load? ...
about 1oomv and the right channel is blowing the fuses.
EchoWars on the AudioKarma forum:
As a semi-poll, I'd like to see those on this board whip out their
multimeters and take a look at the DC that is being presented to the
speakers. This means..
1. Speakers disconnected (or connect the meter to the 'B' speakers and set
the front panel speaker control accordingly)
2. Input set to an unusued position (not Phono)
3. Volume control at minimum.
4. Balance in center
5. Tone controls either defeated or set to mid position
6. Set your meter to read DC, and set to a low scale (300mV scale is
common) Connect directly to the Pos and Neg of the speaker terminals
7. Give the amp 10 minutes to settle. Report back...I'd like to see how
healthy all these old amps are.
If you read:
0 - 15mV: Damn good!! If you read '0V', you may have a capacitor output,
or your meter is set wrong
16mV - 50mV: An acceptable value, especially at the lower end of this
range. 2nd harmonic distortion is probably twice to four times what
manufacturer's spec calls for at higher frequencies. Probably not audible,
as the distortion is mostly in the upper octaves. At the upper end of this
range I begin to raise an eyebrow.
50 - 85mV: Something is certainly amiss, and while this is not enough to
put your speakers or equipment in jeopardy, the amp is running nowhere
near where it should. I'd venture to guess that most of the DC-coupled
amps that are in use by forum members here fall into this range.
100mV to ?: A high enough voltage will cause the DC protection to kick in.
This happens at a level determined by the designer, but is usually
equivalent to about a diode drop (600mV)or so. Needless to say, if you are
listening to an amp with 100mV or more of DC offset, you have no idea what
the amp really is supposed to sound like. Indeed, some amps without a
differential input are actually designed to have a bit of DC at the
outputs, but this is triple-rare, and I don't think anyone here owns one.
(in my book it's piss-poor design, but if you can sell it WTH..)
Soooooo...go grab a meter and tell me what you find...
http://www.audiokarma.org/forums/showthread.php?t=5634
that offset voltage can only cause blown
fuses in case of a shortcircuited load. Have you had a scope on theI don't have a scope... yet.
loudspeaker terminals?
Do NOT rush soldering until you know more about what takes place.I'm still doing some diagnostic testing.
Here is what I have so far:
selector to aux 1
16 ohm speaker load
volume turned all the way down
tone controls and balance set to mid
unit has no speaker relay that delays speaker connection
Left channel when power switched *on* using analog meter across left
channel speaker outputs:
1. DC volts goes to 16-17 volts
2. Goes down to 7-8 volts
3. Goes back up to 14-15 volts
4. Goes down to negative 9-10 volts
5. Voltage stabilizes at 125 mv (using digital meter)
Left channel when switched *off* using analog meter across left channel
speaker outputs:
1. Voltage goes to 5 volts and back to zero
Right channel when switched *on* using analog meter across left channel
speaker outputs:
1. DC volts goes to 16-17 volts
2. Goes down to 7-8 volts
3. Goes back up to 14-15 volts
Goes down to negative 9-10 volts
5. Voltage stabilizes at 100 mv (using digital meter)
Right channel when switched *off* using analog meter across left channel
speaker outputs:
1. Voltage goes to 5 volts
2. Voltage goes to negative 6-7 volts and back to zero
With pre-amp to main amp jumpers removed
Left channel when switched *on* using analog meter across left channel
speaker outputs:
1. Voltage goes to 3.5 volts
2. Volt stabilizes at ~116 mv
Left channel when switched *off* using analog meter across left channel
speaker outputs:
1. Voltage goes to 3.5 volts and back to zero
Right channel when switched *on* using analog meter across left channel
speaker outputs:
1. Voltage goes to 3.5 volts
2. Volt stabilizes at ~108 mv
Right channel when switched *off* using analog meter across left channel
speaker outputs:
1. Voltage increases slowly and then suddenly to 3.5 volts and then back
to zero
As I recall, the DC voltage jumping around at the speaker outputs is
actually fairly typical for a Harman Kardon until it "settles down" after
turn-on.
The original symptom of blowing a speaker fuse suggests that if there was no
DC problem at the moment of failure, then there is a load problem - a short,
probably a loose strand of speaker wire or some such.
Regarding a possible DC problem:
If you were listening at the time of the failure you would have heard a loud
POP and or HUM prior to the fuse blowing. If not, this further suggests a
load problem, and not an amp malfunction.
Mark Z.
Mark,
I can find out if the right speaker is the problem by changing the
speaker hookup at the back of the receiver. If the left speaker fuse
starts blowing, then i know it's the speaker. If the right speaker fuse
keeps blowing then it's the amp. But maybe neither fuse will blow because:
I just finished changing all the lectro caps in the signal paths and
found out about DC offset voltage here:
Amplifier Distortion, DC-Offset, and You!
http://audiokarma.org/forums/showthread.php?t=5634&highlight=offset
The thread is over 1000 posts long but most of the meat is in the the
first post. Later in the thread the OP suggests swapping out the "input
differential pairs" to deal with high DC offset readings. After finding
out what input differential pairse and where they were in in the HK930 I
am working on, I swapped them out and that brought the DC offset voltage
down to respectable levels.
Jack
Let the group know if this cures your problem. In my (limited) experience, 70s SS
gear can be cured of all sorts of weird problems by spending some time changing
out all the electrolytics.
.
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