Quadra 840AV: No A

#1 Thu, 3 Jan 2013 - 20:00

Something ... happened

I got my 840AV plugged in and was having some boot issues. At that point I checked the logic board and noticed several leaking caps so I pulled it, cleaned it and recapped it. I put it all back together, sorted my boot issues, reloaded the original System 7.1 from the 840AV install media and all was well. Nice, clear, strong sound from the internal speaker.

I went and installed some of the optional installs (AV apps) and restarted. The "bong" was cut short half way through and ever since then the audio has been nearly nonexistent from the internal speaker. If you turn the volume all the way up you can hear a faint sound from the speaker. The audio out/headphone works just fine.

So I tried a known good power supply: nope. I tried a known good speaker: nope. I removed all the caps and replaced them again: nope.

I have a fear that something in the audio amp circuit went south. The problem is I don't quite know where to start looking. After close inspection, nothing on the board looks physically bad.

#2 Thu, 3 Jan 2013 - 20:36

well if we look closer at it, We'll notice the sound chip, maybe amp, I'm sure we can scavenge the proper chip(s) from a junk board.

again there wasn't any funny traces that were routed under the caps? Like how they do with the SE/30?

#3 Thu, 3 Jan 2013 - 22:05

Is the audio out just as quiet as the internal speaker, ie. no amplification? I'd check the internal speaker header/traces next.

The speaker that comes in 8x0 and 8x00 cases is very fragile, and often pushed in during an upgrade - I know I've done it

#4 Thu, 3 Jan 2013 - 22:09

The audio out is fine. A known good speaker from an 8500 is barely audible.

#5 Thu, 3 Jan 2013 - 22:15

this issues stinks of SE/30…

#6 Thu, 3 Jan 2013 - 23:16

Here is the amp chip - DA7052A at U23. Pin connections to the speaker outputs and the capacitor at C48 are solid.

Here's a larger version

#7 Thu, 3 Jan 2013 - 23:57

I went for broke, floated a DA7052A off of an old Q610 board and transplanted it. The speaker in the Q840AV lives again. I see that these amp chips are just over $1 at Mouser and DigiKey.

Hopefully this one won't blow up like the old one but I'm calling it "case closed" for now.

#8 Fri, 4 Jan 2013 - 00:01

you are the man! Good Job!

Hopefully I at-least provided a little motivation :-D

So again, how did you get the new one off and on? what was the technique you used?

#9 Fri, 4 Jan 2013 - 00:13

this is good info, you should do a "Caps! -- For the LB", and then link this thread in the main post.

here is a close up of the chip you replaced.

Screen shot 2013-01-03 at 7.10.40 PM.png

#10 Fri, 4 Jan 2013 - 00:23

how did you get the new one off and on? what was the technique you used?

Um, a dangerous and irresponsible way - a heat gun and flux to float it off the board. A plain old soldering pencil to put it on. I don't suggest the heat gun method. I think snipping the legs off of the chip, then removing the legs from the board with a soldering pencil would be best method. I just didn't want to destroy the donor chip because I was going to reuse it.