Infinity Basslink constant rumble - diyAudio
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Old 31st January 2013, 12:12 AM   #1
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Default Infinity Basslink constant rumble

Hi all,

I'm hoping some of you seasoned veterans on this forum have some ideas on what ails this blasted Infinity Basslink (I). The long and the short of it is that when I turn on my car, the Basslink just "hums" or "rumbles" as though it's receiving a constant bass signal, even with the RCAs unplugged. I can make it stop or start doing that again by striking the casing of the hard enclosure, or if I plug in the RCAs it will try to respond to the music but is drowned out by the constant bass sound. The power LED comes on and stays on, but the servo indicator LED never lights. I've taken it apart, gotten my multimeter out and even fixed a few potential problem components, but it still does it.

Help???

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For those interested, here's how it got to this point:

The Basslink was installed professionally in a previous vehicle and worked fine for a time. At some point, it started behaving erratically. When the car turned on and the Basslink's integrated amp received the remote turn on signal, about half the time the Basslink would just start blasting as though it was receiving a constant bass signal. It would stop after a few seconds, after which it wouldn't thump to the music, either. It could be remedied by knocking/hitting/rapping on the casing of the subwoofer, after which it would work normally usually until it powered off again. This was a few years back and we no longer have that car, so I didn't think about it for a long time.

Recently, I got interested in hooking it up again. Call it nostalgia. My car has a stock 8" subwoofer, so I used a line out converter to tap into the speaker level inputs to that. Power and remote run down one side of the car, totally separate from audio lines. The unit is grounded to a stock bolt underneath the trunk lining which was used to ground some pre-existing stock component of my car.

So I hooked everything up and it still did the constant on thing. Somewhere in some forum I found someone suggesting that the gain knob was the culprit, and that pushing/pulling on it would modulate the effect. BINGO. It did.

So I took apart the unit, desoldered the existing knob and soldered on a new OEM one from the manufacturer. After I hooked it back up, it still did the constant-bass thing, but was unaffected by the gain knob. I could still make it stop/start by hitting the unit.

So I took it apart again. I noticed on the amp's circuit board that the copper trace that connects to the ground post had been BURNED to the point of having a very tenuous connection. I fixed that by soldering a short piece of stranded copper wire onto the trace and verified that the resistance across the board (from screw to post) on that trace was roughly zero (0.75 Ohms).

I hooked the unit back up, proud of my work and convinced that the broken trace had to have been causing a ground issue. BRRRRRRRRRRRRRRRRRMP! No change in behavior.

I called around and there are no authorized Infinity repairers that work on car audio in my area.

Any ideas what to do next? (I know the practical answer is to toss out the Basslink and get a REAL system, but I like fixing things like this because I learn so much in the process.)

Last edited by IDiggity; 31st January 2013 at 12:23 AM.
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Old 31st January 2013, 01:52 AM   #2
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You mentioned a 'servo'. That's generally used to provide feedback from the speaker to the amplifier.It's possible that that circuit is damaged or there is a loose connection on the speaker or feedback device.
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Old 31st January 2013, 03:34 AM   #3
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I'm looking for it, but not finding anything. If it helps, I've got the service manual for my model: [Dropbox]

It has the amp circuit diagrams and PCB layout and all that good stuff.
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Old 31st January 2013, 03:37 AM   #4
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Quote:
Originally Posted by Perry Babin View Post
You mentioned a 'servo'. That's generally used to provide feedback from the speaker to the amplifier.It's possible that that circuit is damaged or there is a loose connection on the speaker or feedback device.
I've been looking for it, but not knowing what I'm looking for, I'm not spotting any other problems on the circuit board.

If it helps anyone, here's the service manual for my unit, including the circuit diagrams and PCB layout, etc: Dropbox
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Old 31st January 2013, 04:17 AM   #5
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Do you have a scope?

Did you confirm that you have 15v on the power supply pins of the op-amps?
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Old 31st January 2013, 04:52 AM   #6
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Quote:
Originally Posted by Perry Babin View Post
Do you have a scope?

Did you confirm that you have 15v on the power supply pins of the op-amps?
All I have is a DMM. I haven't ever attempted to hook up just the main board or the entire torn-down assembly in the trunk of my car (the only 12V DC power source I have).
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Old 31st January 2013, 06:17 AM   #7
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I have the same document you have.
I have worked on a few of these also and found repeatedly the lower rail supply diodes would fail. This was a very common issue on several I repaired. So Perry is very correct in asking you to check those lower rails first..... I think I still have a complete module around here some where

Last edited by 1moreamp; 31st January 2013 at 06:21 AM.
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Old 31st January 2013, 06:14 PM   #8
Satyr is offline Satyr  United States
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Hey there-
I don't know if this helps or not- but we had the exact same issue with a bazooka tube with built in amp. It was configured during install to "sense" the signal from the deck's line level or rca outputs and turn on automatically. (In our case- it was hooked up to the rca's.) The place that did the install didn't hook up the remote turn-on lead, even though the rca's had one in it. So, when the deck was powered off and the car shut off- the amp in the bazooka would stay powered. After a short while boooooooooooom. It was like some sort of weird ground loop reverberation thing. The fix? If the bazooka is hooked up to the remote turn on lead, it shuts down with the deck when the deck is turned off, and since the the amp in the bazooka isn't powered- no boom. I figured this out by experimenting with it- but we still need to hook up the remote turn on lead. Right now- we just have the bazooka disconnected. Hope this helps.
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Old 31st January 2013, 07:54 PM   #9
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Quote:
Originally Posted by 1moreamp View Post
I have the same document you have.
I have worked on a few of these also and found repeatedly the lower rail supply diodes would fail. This was a very common issue on several I repaired. So Perry is very correct in asking you to check those lower rails first..... I think I still have a complete module around here some where
Very interesting.....

I'll admit that I don't know enough about integrated circuits to know exactly what you're talking about when you say "lower rails." I vaguely remember hating problem sets with op-amp problems when I had to take circuits back in college.

Can I test this with the unit powered off with just my DMM? I'll look at the diagrams and try to make sense of what you say, but in the probable outcome that I can't figure it out, would you mind posting a pic?

Many thanks to all for thinking about this.
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Old 31st January 2013, 08:01 PM   #10
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Quote:
Originally Posted by 1moreamp View Post
I have the same document you have.
I have worked on a few of these also and found repeatedly the lower rail supply diodes would fail.
Are we talking about diodes D105 and D106 per the service manual?
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