Subwoofer Died

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71340Duster

71340Duster

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I have an Infinity Basslink in my Suburban that was making an occasional thump while playing like the mute circuit wasn't working and it was self power cycling. It played though but does not any longer. I get a power up light but no sound. I took the mother/main board out, think the problem is there. I've found a shorted diode (D108) and some off value resistors. If you look in the pic it happens to show the discolored area of the board I'm looking into. I was hoping the diode was a 1N4148 but it's not, will have to see how many of this vintage parts are available, main audio amp is a class D made in China special, replacement cost is $15, I don't think it's the issue tho. Any comments/suggestions would be appreciated, I'll post my progress if there is any HA!!!

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Schematic.jpg
 
I'm sorry I didn't read your post. all I did was read the title- subwoofer died? All I could think was yippee another one of those boom boom things I don't have to listen to....
 
That's considerate, about all I do is turn it down when coming into my neighborhood. Here's my head unit, 2003 vintage, no bells and whistles, just clean sound.

CD-400
 
That D108 might be a zener, to get the right reverse voltage for regulation use exact replacement. I am using my phone to read schematic, so not sure.
Things to check is the boost supply for the D-amp. It will be bi-polar, that means a +, and - outputs around 30V. Could be more or less depending on power rating, the +, and - voltages should match.
 
KitCarlson said:
That D108 might be a zener, to get the right reverse voltage for regulation use exact replacement. I am using my phone to read schematic, so not sure.
Things to check is the boost supply for the D-amp. It will be bi-polar, that means a +, and - outputs around 30V. Could be more or less depending on power rating, the +, and - voltages should match.
Click to expand...

Right you are, saw that for myself in a printed version of the schematic today. The source should be higher than 15vdc by a bit you are probably pretty close with the 30vdc. I'm going to change out a couple of zeners first, we lifted one end of D108 just to be sure it was shorted, also will change out a couple of precision resistors in the regulator. Then I'll power it back up and sniff around, thanks for the boost supply idea I'll check that then.
 
I had a few moments to find the block diagram is helpful. It shows + - 15V, and 56V supplys. If any of those go down, you will hear a thump. The D108 is with the +15V supply. Things like bad caps, bad solder connections, or like you found, bad diode. There is a relay that turns on the speaker, for protection, and to eliminate thump on power up by delaying.
 
I think I got lucky, changed one zener (D108) and replaced two precision resistors (3.3k 5%) with 3.3k 2% as one was reading 3.8k. Both the 15 volt plus and minus checked good along with the 50'ish plus and minus high voltage. The audio sources we had in the shop did not go very low but we were able to cob together a 3.5 mm cable and run music out of a phone, had sound out of the woofer. Going to install the sub along with the my recently repaired 6 channel amp and see what I have. Thanks to all the posters, hopefully I'm done with this Infinity Bass Link and there's no more issues.
 
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