Channel blown on Soundstream amp

[antimatter]

Hello everybody. New to this forum not new to car audio or electronics. I feel i have enough skill to complete a repair job on my amp just not enough knowledge. I was hoping some of the kind people here could point me in the right direction

First off I have a Soundstream D'artagan 5.1 amp. Its basically just a six channel amp (no on board sound processing)

The center channel (5th) is not operating properly. Let me describe the symptoms. With the volume all the way up on the center channel i can hear soud but very low. It isn't crisp either.... It sounds a bit fuzzy or staticky.

Now I opened the amp up to look for chared compnants, blown caps or burn marks to find none. I know the next step is to get a multimeter with short circuit detector and test for shorts between the transistors.

I will do this but i was wondering if someone can give an oppinion that has had experience with this on what componant they think is blown.

I will be uploading pictures of the board as soon as I return home from work,

Thanks to all that read this far and thanks in advance to everybody who replies

[zagisrule!]

Sounds to me like you have a bad gain control pot for that channel.











-Matt

[antimatter]

Thanks for your reply

How would i go about testing it?

If i hook up a multimeter to it to test resistance and adjust the dial and compare it to a base test from a know working pot, will this tell me if it is bad or not.

Sorry i havent posted pictures. I ended up talking to one of the Electrical Engineers at my work that i am friends with. He told me to bring in the amp, so right then and there i took it out of my car and left it with him.

He was asking for a schematic but i figure that getting one would be out of the question.

These guys are usually pretty busy so i can expect that my amp is going to sit on his desk for a while so i will probably fix it on my own. I will test out the pot on the 5th channel but if anyone knows how to tell of they are working properly do let me know

Thanks

[zagisrule!]

You need an ohm-meter.

What you need to do is measure resistance from the center pin of the channel 5 pot to both the outside pins of the pot. Write down the measurements and now repeat the same procedure for all the other pots.

If all is good, you will probably have a table of values that are all similar on each side of the pots. You want to see if the channel 5 pot is measuring the same resistance as the others.

Measuring in-circuit is NOT ideal, but it will show you which pot(s) are bad.

The bad pots can then be replaced (check all the adjustments, filter pots, gain, etc) and make sure to find out if the pots need to be log or linear taper.



-Matt

[Dr. Photon]

if there's a built in crossover or any other controls that can affect the center channel, check them too. I would also check for bad solders and cracks in the circuit board. With a function generator and an osciloscope (I'm sure your EE friend would have access to them), you can trace the signal from input to speaker out and see where the problem lies. You can also detect ultrasonic oscilations like this

One good thing about these amplifiers is that at least 5 of the six channels (I'm assuming the 6th channel is a sub channel and that it's "bigger") are the same, so you can simply compare with one of the working ones.

[antimatter]

Thanks for the replies.

All of the gain pots appear to working fine (compared to the known working ones), Man it sucks being withough music

But i would like to have the center channel fixed. I will tell the EE about checking those things.

He said he checked the FETS and they all looked tested out okay, and besides i have seen some of these things when they go bad and usually they don't go quietly.

[Dr. Photon]

usually if the output devices (MOSFETS or bipolar transistors, depending upon amplifier design) and their driver transistors are fine, it's probabally going to be a bad solder, loose connection, output relay contacts (car amps don't usually have these) cracked board, bad connector, or bad pot (generally, a "mechanical" problem).

You have already ruled out the power supply, since if that blew, none of the channels would have worked.