Question about Dell ADA745 Computer Speakers

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ADA745 speakers have no output

The 5 speaker system worked great for two years, then just stopped outputting any sound.  The sub powers up and the satellite speaker powers up but no sound.  I tried hooking them up to two other computers with the same result.  I opened the back of the sub to look at the circuit card and there were no obvious problems such as burnt areas on the board and the output drivers appeared to be ok.

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  • majpue Nov 04, 2007

    Same thing here; they just gave out after a long time of solid sound. It may help that the sound "faded" out on mine. Each day I had to turn it up a little more to get the same amount of sound. Eventually it was at 100% on the computer and speakers, and it faded to a whisper. Also, I can hear static when the speakers are turned up high, so they're obviously getting power, and can obviously output sound.

  • js3131 Nov 10, 2007

    Also had system 3 years with no problems. Failed suddenly. Speakers do not work on other pcs or other devices. Other speakers work fine on pc. Unplugged speakers and tested 3 of 4 with another device and they work fine. Only supwoofer/power supply seems to be broken.

    I contacted Altec Lansing and they confirmed subwoofer problem, not repair or replacement is available.

    This seems like it could be a single component in the subwoofer. Any advice on how to fix or service sources would be appreciated.

  • vbkkpr95 Nov 18, 2007

    Same speaker just stopped working ( 3 years leaving subwoofer on). The fuse looks good, but was going to change just to see. Thought I would search for answers first... here I am. I do hear a high pitched whine from one speaker? but have tried all avenues, except Dell. Figured I would know more then their book that is just like mine... Anyway, do I just purchase another set of speakers??? what is a good suggestion if I do need to just purchase new speakers? Thanks ahead of time...

  • Joel Downey Dec 28, 2007

    Same problem as others posted. Sound is beginning to fade. I have read that leaving the system on causes the power transformer to fail. I don't know if this is true, but I took mine apart a few months ago, and the power transformer was very hot. As it turns out, if I turned it off and let it cool back down, it started working again after power up. As a check, you can feel the four mounting screws on the bottom of the case. I noticed that the four bolts on the bottom of the sub woofer case (which are holding the power transformer in place) get hot enough to be mildly painful to touch due to being so warm.



    I am an electrical engineer, and if what I have read is true, I'm tempted to open it up, power it on and monitor the DC supplies as the unit warms up to see what happens. If the transformer output starts decreasing with time (as temperature hoes up), I guess that would confirm it. An option, if you have enough knowledge of how power supplies work, is to find an appropriate replacement transformer, or multiple transformers if you can't find one with multiple outputs. I don't remember how many outputs the transformer had, but I think it was more than one. I suppose I'll need to do the checkout and see what I can find out. If I need multiple transformers, then I'll need to rig up a custom mounting fixture to hold them.



    If I ever get around to it, I'll let you know what I come up with.


  • Anonymous Dec 29, 2007

    Back again.



    Well, this is a long story with a possible solution. I looked at the power supplies. They are OK. There is no transformer problem, at least with my unit. The issue I have is with the VCA (voltage controlled amplifier) on the amplifier board. There is a voltage signal which comes form the right front speaker, which controls the volume for all channels. The higher the DC voltage (up to 5.2 volts) the more volume. It appears as if there is not enough voltage at pin 10 and 8 of this I.C. You can find a data sheet here if you are interested.



    http://documentation.renesas.com/eng/pro...



    I'm only getting about 1.2 volts at the pin, and consequently not much volume. If I artificially increase the voltage, I get much more volume, like I would expect. I have checked out the components on the right front speaker PCB (Printed Circuit Board), and they are OK. There is only one component on the main PCB other than the two VCA ships, and it is a 1uF cap, which I removed to see if it was leaky. I found no increase in voltage, so the cap was not it. Something is loading the voltage signal going to the VCA chip. The only thing left on the PCB are the two I.C.s, so they must have a problem.



    A possible solution would be on the right front speaker PCB. There is a 33kohm resistor in series with the volume control potentiometer. I calculated the voltage one should get at the I.C. pin, with the values of the components on the right front speaker PCB, and it comes out to 5.3 volts maximum, which agrees with the IC spec. This assumes almost no load (current draw) at the VCA chip input. If I calculate the load at the I.C with the voltages I am seeing, I get something around 5kohm, which is way too low for the component values on the right front speaker PCB. (it also is way too low based on the I.C.'s internal schematic, so my assumption of an I.C. issue seems to be confirmed) I also measure the pin input resistance with the power off, and it shows about 4.5kohm.



    I tacked a 6.8kOhm resistor in parallel with R1 on the right front speaker PCB, and now I have the volume back. A minor problem with this approach is that the taper on the volume control has been altered some. The volume comes up much quicker than before, so be careful as you turn up the volume. I don't know how long that will work either. If the VCA chip continues to degrade, then the fix might only be temporary. Probably the "right" fix would be to replace both VCA chips on the board. However, that is a pretty intense task unless you are used to doing that kind of work, and have the proper equipment.



    If you have the same issue as what I had, here's how you can fix the problem. Disconnect the right front speaker from the sub woofer. Remove the two screws which attach the base of the speaker to the speaker housing. Remove the small screw under the base, found on the back of the housing. Next, you need to remove the grill. The grill is just pressed on, so you need to work a sharp object under the grill at the top and carefully pry it off. There are four screws holding the housing together. Remove them from the front. Once you have the housing apart, you can see the small PCB mounted to the front of the enclosure. Pull volume knob off the front of the enclosure. Remove the two screws holding it in place. Locate R1 on the front of the PCB. It should have four colored bands, orange, orange, orange and I think gold. (I'm doing this from memory, sorry!!) The others have grey bands, so don't use those. Now the work requires some minor skill. If you can solder, you are in good shape. I soldered the 6.8 kohm (6800 ohm) resistor on the "back" of the board, where all the copper traces are, connecting it to the same solder pads as R1. If you happen to get it across one of the other resistors, it won't hurt anything, but it won't work either. If you don't have a soldering iron, it might be possible to twist the leads of the new resistor around the leads of R1 on the top of the board. I think a 10kohm resistor would work well too, but I had the one I calculated would make it work like the original configuration so I used it.



    You can try things out before you put the speaker together, to see if this fixes the problem. Turn the RF speaker off, and plug it back into the sub woofer. Start an audio source, and turn the right front speaker back on, and slowly bring up the volume. If you are lucky, this will fix (at least for a while) the problem.



    Having figured this out, I still think the internal temperature in the sub woofer enclosure is too high. This might be what caused the VCA chips to degrade in the first place. While turning the volume control on the RF speaker does not "turn off" the speaker system, it does shut off most of the devices on the amplifier board. The main power supply voltage (rail to rail) is 35.3 volts with only the sub enclosure switch on. Turning on the Right front control reduces the rail to rail voltage to about 34.3 volts, and the transformer begins to heat up. I ran the unit this morning for about 20 minutes with just the sub powered, and the transformer did not heat up appreciably. After turning on the rest of the speakers, the power transformer temperature probably increased about 15 degrees C in 30 minutes. The temperature attained is really quite cool for a transformer, but inside the sub woofer enclosure, with no place for the heat to escape, it could get much warmer. At the least, I would turn off the right front speaker whenever you are not using the speaker system, especially at night if you turn off your PC. From what I saw this morning, that should keep things pretty cool. However, if you want to be absolutely sure you don't make things worse, turn off everything at the sub woofer switch.



    That's all I had. Hopefully this helps someone.


  • dcproduction May 29, 2008

    I was setting up new computer with these speakers. I heard the beginning of the windows login sound then it cut out and never heard a thing since. The microphone works and it shows the speakers work in the diagnostics but still no sound.

  • JamBox Sep 01, 2008

    My father gave me this system when i went off to school, when i got to school i plugged it in and wasn't working. all the speakers and subwoofer had power but there was no sound. it spontaneously started working again later in the year but was flaky and worked at a volume relatively low compared to other systems in the dorm. right now it's not working and i've been looking for an easy solution but haven't been able to find one.

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Had the same issue as treefarmer and guest. Initially I thought that the voltage controlled pre-amps were the problem as well but further testing proved that wrong. If you remove the yellow wire from the RT Front speaker PCB and measure the voltage at the wiper of the pot it is still too low (should swing from 0 to 5 volts). On investigation it turned out that the pot was failing.

I couldn't find a proper replacement pot so had to fix the broken one. After removal and dissassembly it discovered there was a leakage path between the carbon trace and the bushing assembly. The top deck which contains the carbon path for the wiper can be removed by bending back the tabs that hold it to the metal case. Carefully cleared the shorting path with a probe and retested with an ohm meter..

Re-installed and wala it works!

Posted on Nov 04, 2010

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