Harman Kardon SUBTS15 subwoofer very faint sound

[170watt]

I have a Harman Kardon SUBTS15 subwoofer with problems. I would like to try fixing it myself. I have basic troubleshooting experience (including soldering skills), but I don’t know what I should next (besides tossing it).
Here’s what it does, and what doesn’t.
When I power it up, the front led lights amber, and after a couple of seconds turns blue (and stays blue). At that moment you can hear a loud thump (couple of thumps actually). While on, there is no sound coming from the speaker. If you feed a signal (at the line level, with test tone from receiver), you can hear it extremely faint (the volume does not modify that). When powered down, another thump.
What I checked: the relay works both when turning on and off (both times coincide with the thumps). The +/- 15 V are both OK. At the visual inspection, there is some discoloration (darkened color) of resistor R146 and 149 (especially 146 that looks a bit burned) but both test correctly 330 ohms. The PCB around them also looks a bit darkened.
Any idea where to look for? I doubt that the issue comes from the “darkened” area. The troubleshooting flow chart does not help, as the led does not turn red or green (only blue, and stays blue).

 

[William Sommerwerck]

According to the owner's manual, what do the various LED colors indicate?

The thumps suggest that the output stage is receiving power. That you can't
get anything out of the woofer suggests that the signal is getting "hung up"
somewhere before the output stage.

Also make sure that all the settings are correct.

Note that the test signal has to have significant components in the range the
woofer is designed to to reproduce.

 

[Arfa Daily]

"170watt" <170watt@gmail.com> wrote in message
news:cb331a2f-c3e6-48e5-96c0-e059cb118892@googlegroups.com...

I have a Harman Kardon SUBTS15 subwoofer with problems. I would like to
try fixing it myself. I have basic troubleshooting experience (including
soldering skills), but I don’t know what I should next (besides tossing
it).
Here’s what it does, and what doesn’t.
When I power it up, the front led lights amber, and after a couple of
seconds turns blue (and stays blue). At that moment you can hear a loud
thump (couple of thumps actually). While on, there is no sound coming from
the speaker. If you feed a signal (at the line level, with test tone from
receiver), you can hear it extremely faint (the volume does not modify
that). When powered down, another thump.
What I checked: the relay works both when turning on and off (both times
coincide with the thumps). The +/- 15 V are both OK. At the visual
inspection, there is some discoloration (darkened color) of resistor R146
and 149 (especially 146 that looks a bit burned) but both test correctly
330 ohms. The PCB around them also looks a bit darkened.
Any idea where to look for? I doubt that the issue comes from the
“darkened” area. The troubleshooting flow chart does not help, as the led
does not turn red or green (only blue, and stays blue).

The full service manual is available for free here

http://elektrotanya.com/harman_kardon_sub-ts15_sm.pdf/download.html

If you've never used Elektrotanya before, first left-click on the thumbnail.
That will open it into a bigger window. Then use the "X" on that window to
close it. Now look in the text below the thumbnail, and you should see a
tiny and underlined "processing" in the middle of the text. Wait a few
seconds, and this will change to an underlined "Get Manual" Now left-click
on this, and it will open a link to the manual PDF.

Do not click on any large buttons on the site that say "Download", as these
just take you to helper software sites. You don't need to be a 'member' or
to log in, although this limits you to two downloads per day. The site is
'clean' and in a long time now of using it, I've never had any issues.

The schematic looks quite straightforward, and there is a good block
diagram, so you shouldn't have any problem tracing what is amiss with it.

Arfa

 

[dave]

On 07/18/2013 01:00 PM, 170watt wrote:

I have a Harman Kardon SUBTS15 subwoofer with problems. I would like to try fixing it myself. I have basic troubleshooting experience (including soldering skills), but I don’t know what I should next (besides tossing it).
Here’s what it does, and what doesn’t.
When I power it up, the front led lights amber, and after a couple of seconds turns blue (and stays blue). At that moment you can hear a loud thump (couple of thumps actually). While on, there is no sound coming from the speaker. If you feed a signal (at the line level, with test tone from receiver), you can hear it extremely faint (the volume does not modify that). When powered down, another thump.
What I checked: the relay works both when turning on and off (both times coincide with the thumps). The +/- 15 V are both OK. At the visual inspection, there is some discoloration (darkened color) of resistor R146 and 149 (especially 146 that looks a bit burned) but both test correctly 330 ohms. The PCB around them also looks a bit darkened.
Any idea where to look for? I doubt that the issue comes from the “darkened” area. The troubleshooting flow chart does not help, as the led does not turn red or green (only blue, and stays blue).

Check for DC on the ouput. Anything above 50mVdc indicates issues with
the power amplifier stage.

 

[dave]

On 07/19/2013 12:26 PM, 170watt wrote:

On Thursday, July 18, 2013 4:00:45 PM UTC-4, 170watt wrote:
I have a Harman Kardon SUBTS15 subwoofer with problems. I would like to try fixing it myself. I have basic troubleshooting experience (including soldering skills), but I don’t know what I should next (besides tossing it).

Here’s what it does, and what doesn’t.

When I power it up, the front led lights amber, and after a couple of seconds turns blue (and stays blue). At that moment you can hear a loud thump (couple of thumps actually). While on, there is no sound coming from the speaker. If you feed a signal (at the line level, with test tone from receiver), you can hear it extremely faint (the volume does not modify that). When powered down, another thump.

What I checked: the relay works both when turning on and off (both times coincide with the thumps). The +/- 15 V are both OK. At the visual inspection, there is some discoloration (darkened color) of resistor R146 and 149 (especially 146 that looks a bit burned) but both test correctly 330 ohms. The PCB around them also looks a bit darkened.

Any idea where to look for? I doubt that the issue comes from the “darkened” area. The troubleshooting flow chart does not help, as the led does not turn red or green (only blue, and stays blue).

Thanks for your answers. I haven’t used this forum before, I think I inadvertently deleted one post, and also was not sure how to reply specifically to the author, I might have done this already, sorry for double posting.
@Dave:
I checked the DC output, it’s below 10mV.
@ William:
The color LED mentioned in the user manual are amber and blue (normal functioning). The troubleshooting diagram in The Service Manual also mentions green and red, which is confusing. The test signal was generated by the receiver, with the signal test function activated, via subwoofer pre-out.
@ Arfa
I have the manual, from the same source you mentioned.

If you have a diagram and a scope you know what to do.

 

[170watt]

On Thursday, July 18, 2013 4:15:32 PM UTC-4, William Sommerwerck wrote:

According to the owner's manual, what do the various LED colors indicate?



The thumps suggest that the output stage is receiving power. That you can't

get anything out of the woofer suggests that the signal is getting "hung up"

somewhere before the output stage.



Also make sure that all the settings are correct.



Note that the test signal has to have significant components in the range the

woofer is designed to to reproduce.

The user manual only indicates the amber and blue (normal) colors, whereas the green and red are mentioned in the service manual, which is confusing. The test signal was generated by the receiver, for the subwoofer channel. The "normal" sound, played during music reproduction cannot be heard.

 

[170watt]

On Thursday, July 18, 2013 4:00:45 PM UTC-4, 170watt wrote:

I have a Harman Kardon SUBTS15 subwoofer with problems. I would like to try fixing it myself. I have basic troubleshooting experience (including soldering skills), but I don’t know what I should next (besides tossing it).

Here’s what it does, and what doesn’t.

When I power it up, the front led lights amber, and after a couple of seconds turns blue (and stays blue). At that moment you can hear a loud thump (couple of thumps actually). While on, there is no sound coming from the speaker. If you feed a signal (at the line level, with test tone from receiver), you can hear it extremely faint (the volume does not modify that). When powered down, another thump.

What I checked: the relay works both when turning on and off (both times coincide with the thumps). The +/- 15 V are both OK. At the visual inspection, there is some discoloration (darkened color) of resistor R146 and 149 (especially 146 that looks a bit burned) but both test correctly 330 ohms. The PCB around them also looks a bit darkened.

Any idea where to look for? I doubt that the issue comes from the “darkened” area. The troubleshooting flow chart does not help, as the led does not turn red or green (only blue, and stays blue).

Thanks for your answers. I haven’t used this forum before, I think I inadvertently deleted one post, and also was not sure how to reply specifically to the author, I might have done this already, sorry for double posting.
@Dave:
I checked the DC output, it’s below 10mV.
@ William:
The color LED mentioned in the user manual are amber and blue (normal functioning). The troubleshooting diagram in The Service Manual also mentions green and red, which is confusing. The test signal was generated by the receiver, with the signal test function activated, via subwoofer pre-out.
@ Arfa
I have the manual, from the same source you mentioned.

 

[Arfa Daily]

Thanks for your answers. I haven’t used this forum before, I think I
inadvertently deleted one post, and also was not sure how to reply
specifically to the author, I might have done this already, sorry for
double posting.
@Dave:
I checked the DC output, it’s below 10mV.
@ William:
The color LED mentioned in the user manual are amber and blue (normal
functioning). The troubleshooting diagram in The Service Manual also
mentions green and red, which is confusing. The test signal was generated
by the receiver, with the signal test function activated, via subwoofer
pre-out.
@ Arfa
I have the manual, from the same source you mentioned.

First, it isn't a forum - it's a usenet newsgroup. If you are accessing it
via the internet, then you will be using a scraper site that acts as a
portal to usenet. Effectively, it's taking usenet content and placing it
onto a website, then taking your replies or original posts, and shunting
them back the other way. It's a 'scruffy' way of accessing newsgroups, and
posts get lost and delayed way too easily. You are much better off accessing
usenet and the groups directly from your own machine. This is easily done
via clients within Windows mail programs - for instance I am using the
client within Windows Live Mail at the moment to post this - but there are
many other free ones. Sometimes, I use XNews for instance. If your ISP
doesn't provide direct access to usenet news servers, there are plenty of
other options. Replying becomes very easy once you have a proper news
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be posted to the whole group, in chronological order, with the text of the
post you are specifically replying to, included above your reply. If you do
want to reply just to a specific poster for any reason, same procedure, but
click on "Reply".

As to your problem. I am not sure how you would have an amber and blue led
indication. Certainly, there are no dual LEDs in that combination that I
have come across. Red and green duals exist, and if you drive both at once,
you get amber. If you have the unit set for auto switch on on receipt of
signal, do any indicators change when you give it some signal ? If they do,
then that should eliminate a good chunk of circuitry around the front end.
As to trusting that the driving source's test signal is putting out
something valid on the sub channel, I'm not sure that I would. Whenever I'm
repairing subs - which is quite often - I use a proper sine generator set to
80 Hz.

Do you have access to a 'scope ? If you do, and the knowledge to use it,
then this should be an easy problem to at least diagnose, if not actually
fix. The fact that you get a thump both at switch on and switch off, seems
to indicate that the output relay is closing and staying closed, which
pretty much - although not quite definitely - suggests that the output stage
is happy and working. If there were any serious DC offsets or whatever, the
output protect relay would drop back out.

This is not a particularly complicated unit, and having a service manual -
even a block diagram - is, as most of us on here would tell you, a HUGE
plus these days. We have to fix this stuff for a living on a daily basis,
with no info at all, probably at least 50% of the time ...

Do some more tests with a known signal going in, and come back to us with
the results. At a pinch, you could use a small power transformer - say 6v -
with a resistive potential divider of 10:1 across it to provide a crude line
level sine wave signal at 50 or 60 Hz, depending which side of the pond you
are. Note, that's a transformer, on its own. Not a DC power unit of any
kind.

Arfa