Alpine MRV-F400 channel 3 no output

[loginfailed]

I bought an Alpine MRV-F400 off of eBay. I tried installing it today and it seems to have no output on channel number 3.

I bought it to replace another smaller Alpine 4 channel amplifier which has been installed and working fine, so I know that it isnt an installation related issue.

I installed car audio professionally from 1994-2005. I have no problem installing equipment, but when it comes to opening said equipment, troubleshooting and making the repairs, that is all new to me.

I specifically purchased this MRV-F400 to go along with an MRV-1000 and one of those heat sink links that joins the two amps together so it looks like one big long amplifier.

Could anyone here point me to what I should be looking for as far as why channel 3 has no output? Here is a picture (not of my amp, but mine is the same as the one pictured)

An externally hosted image should be here but it was not working when we last tested it.

I checked continuity between the RCA jack and the circuit board itself and the connection there is good. I also checked continuity on the other end where output terminals are soldered to the board and that seems to be good as well.

Thanks for any guidance or advice regarding this,

Dwayne

 

[Perry Babin]

Since you didn't say that the channel made the speaker pop, I'll assume that there is no significant DC offset and it's safe to connect a speaker to the defective channel.

It could be a bad connection. With a speaker connected to the defective channel and with signal being fed into it, try moving all controls/switches/pots to see if one is intermittent. If that does nothing, try pushing on the board at various points to see if there is a point that makes the audio play through the defective channel.

It's sometimes difficult to find an intermittent connection with an ohm meter because simply touching the connection with the meter leads can close an open connection.

The information about the RCA jack in the following thread may help.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=112429

 

[loginfailed]

Thanks for the quick reply.

There isnt any DC voltage at the channel 3 output, its just dead open. No voltage of any kind. No pops either that I could hear. When I noticed the channel was not playing, I immediately disconnected everything and pulled the amp apart to look for signs of something burnt or what not. I didnt think to try the stuff you mentioned.

I will try all of the things you suggested tonight when I get a chance to play with it again after I get my kids to bed. Hopefully it will be something as simple as a cold solder joint somewhere. I will report back once I check it out.

I did read that RCA jack thread. That is where I got the idea to check continuity between the jacks and the traces on the circuit board.

Many thanks!

 

[loginfailed]

I removed the board again and cleaned up some of the traces where it looked like some solder joints had gotten hot at some point. It looked like solder rosin had run off from the solder joints or something.

I put it back together and all channels are now playing fine.

Does that sound like something normal that happens? It has been playing fine in the car since Monday with no issues.

Thanks, Perry for your help.

 

[Perry Babin]

If you resoldered the connections that looked like they got hot, it may be OK. If you simply cleaned the flux off of the board, it will probably go out again.

If/when it goes out, try pusing on various parts of the board to see if you can find the area where it's most sensitive.

 

[loginfailed]

Ok, well at least I know if it goes out again all I will need to do is re-solder a few connections.

Thanks for all of your help with the troubleshooting!

 

[jol50]

It could have been a bad solder, it happens. The rosin is normal, the factory leaves it on there sometimes. Often they go back and load up big solders like the transformer/etc.

If it got hot enough to melt solder lots of stuff would happen.