Yamaha YST-SW200 active subwoofer doesn't forward filtered signal on the left side

[George]

Hi Guys,

I bought my Yamaha YST-SW200 subwoofer and my Onkyo R-30 receiver/amp back in 1995 at Circuit City when it was still around and until recently everything was fine. (By the way I am using this setup to play backing track for own entertainment.)

So, about a week ago I noticed that no sound was coming out of the left speaker (in the chain of Onkyo receiver -> Yamaha active subwoofer -> stereo speakers). I jiggled the speaker cables on the back of the receiver and the subwoofer and the left side came alive again. But next day, the same problem happened and messing with the cables didn't help and since then the only way to get sound out of the left speaker if I bypass the subwoofer all together and hook up the receiver directly to the speakers.

I've got a good quality DVOM, an analog scope, also downloaded some test tunes in mp3. I couldn't found a service manual for this subwoofer but I managed to find one to a similar model: YST-SW150.
I also took some pictures of the open subwoofer that you can view here:
Index of /geza/temp/browseable/yamaha_sub

Could you guys help me to isolate the problem? Whether I can fix it, it depends on the details, but the circuit boards that I saw didn't look too complicated.

[The Dude]

Welcome to the place! The first thing I would check would be the solder connections on the speaker terminals themselves since "jiggling" seemed to work at first. On the bottom side of the board you have pictured in IMG 4062.jpg, have a good look at all connections and make sure there is no cracked solder or poor solder joints.

[George]

Today I removed the input panel and checked all solderings visually, didn't find anything suspicious.
I also checked the input jacks and different solderings on the same pcb section for continuity, no problem.
I also redid all 4 speaker wire connections. Uploaded a few more pictures of this pcb to the rest.

After I turned the system on both speakers got signals and I thought, that maybe it was just a bad connection somewhere. But after a few minutes, the left side volume started to fade away and by the time I realized what's happening the left side was deaf completely.

At this time I turned off the Output of the sub-woofer (but left it on), nothing changed, left side stayed off.

Then I turned the sub-woofer off, same thing, no sound on the left side.

Now, the only thing that I can think if is, that one of the components fails as soon as it warms up.

But I think, it is quite interesting that even when the sub-woofer is off, it wouldn't allow the signal to go through itself to the speakers. The only thing that would explain to me is some kind of short in the circuit.

[Jazz P Bass]

Try running a signal into the RCA jacks.

This will help narrow down the issue to the sub itself.

Then again, the schematic shows that the speaker input to output connection is a direct shot.
So if the sub is receiving a good speaker signal, it should pass that signal no problem.

So that leaves a faulty solder joint(s) on that input panel.

No matter that they 'look good'.
Resolder them.

[George]

"Try running a signal into the RCA jacks.
This will help narrow down the issue to the sub itself."


What kind of signal did you mean? A test tune signal from my laptop
OR
one that's designated specifically for sub-woofer coming from a line out port for subwoofer? I don't have any equipment that would have a separate port for sub-woofer.

When I have the whole system on (receiver+subwoofer), the sub is working, only the left speaker doesn't. So, what would be the point of this test? My guess is that it would drive the sub only. I'm assuming that you meant to have this test done by having all speaker wires disconnected from the sub like it says in the user manual on page 7.

Before I posted this reply I did a few additional tests:

1. I turned the system on, and at first there was no sound coming from the left speaker, then 2 minutes later some statics mixed with music came through then the static went away and the music came through perfectly for about 5 minutes. Not because something happened in the woofer after 5 minutes but because that's when I decided to turn off the subwoofer with the remote. I did, and the sound was also gone from the left speaker. I turned the sub back on, nothing changed, there is no sound from the left speaker.

2. I tried to short the matching (corresponding) external red and black jacks with jumper wires from the outside while the system was on, didn't make any difference, so, I think, the solder joints of the jacks should be fine.

3. there is an instruction on page 3 or 4 in the YST-SW150 service manual about idling adjustment, I followed the instructions and the voltage reading was zero mV at having set my Fluke 87 DVOM to DC mV. I am just guessing that this value should be the same for my sub (YST-SW200). This was the last test, that I did, therefore I can assume that by then the sub was in a non-working state.

So there is no voltage on R21 when the sub is on and idling with no incoming signal.

[52 Bill]

2. I tried to short the matching (corresponding) external red and black jacks with jumper wires from the outside while the system was on, didn't make any difference, so, I think, the solder joints of the jacks should be fine.

Have you tried connecting the receiver to the two speakers directly, without the sub? Try this and see if the left side still cuts out. I don't think that there is anything wrong with the sub unit.

3. there is an instruction on page 3 or 4 in the YST-SW150 service manual about idling adjustment, I followed the instructions and the voltage reading was zero mV at having set my Fluke 87 DVOM to DC mV. I am just guessing that this value should be the same for my sub (YST-SW200). This was the last test, that I did, therefore I can assume that by then the sub was in a non-working state.

So there is no voltage on R21 when the sub is on and idling with no incoming signal.

The reading is taken across the resistor with the positive and negative leads connected as shown in the diagram. This sets the idle of the power amp. If it has been working do not mess with it.

[George]

Have you tried connecting the receiver to the two speakers directly, without the sub? Try this and see if the left side still cuts out. I don't think that there is anything wrong with the sub unit.

Yes, I have, I did mention it in my 1st post.


The reading is taken across the resistor with the positive and negative leads connected as shown in the diagram. This sets the idle of the power amp. If it has been working do not mess with it.


Now, you got me there, because indeed I did not pay attention to the right polarity during measurement, I'll have to repeat that measurement. Hopefully it will be around 2mV as the manual says, but if it is different I'm not gonna touch it.

[The Dude]

The speaker inputs come from the receiver into the sub and then go directly back out to the speakers- nothing to do with the sub other than a junction connection. There isn't any processing in the sub before the speaker output- jack to jack. I see only 3 possible reasons you wouldn't have sound out of one of the speakers.

1) The receiver is the problem- not the sub, and is intermittent.
2) The speaker connections on the sub have a problem.
3) Bad speaker wires.

There is no reason to suspect a power amp problem in the sub. It has no bearing on the L&R speakers.

[Jazz P Bass]

To add: the RCA jacks can take any signal from the main receiver.
The crossover to drive the subs is in the sub.

As I stated & The Dude repeated, the speaker in/ out on the sub is a direct connection.
It is plain on the (excellent) photo that you posted & on the schematic.
The sub simply passes the original speaker signal to the speakers as it also utilizes the speaker signal (eek) for it's own purposes.

You need to take a step back & prove where the problem lies.

This statement: "I tried to short the matching (corresponding) external red and black jacks with jumper wires from the outside while the system was on, didn't make any difference, so, I think, the solder joints of the jacks should be fine." seems to show that the problem is not in the sub.

[George]

I forgot about thumb rule No. 1: KISS!

Hey guys,

The problem is solved and I'm a happy camper (again .

You guys were completely right because it seems like I completely forgot to do the basic things besides using my brain.

What I did was, I replaced the wires between the amp and the sub to the same type what I have between the sub and the speakers. Those cables were too long anyway, so I cut them to the right length and used the left over for the other two. But I also sprayed electronic contact cleaning solution to all connections and voila that did it. My guess is that the cleaning spray did the trick. I just feel so pissed (besides being happy) that I haven't done what I do the first thing at any automotive electrical problem.

Thank you all for pointing me to the right direction! (and doing it so diplomatically)

George