Fixing my Crate

[Safari Jack]

Well I picked up a Crate G130CXL over the weekend.  It had problems with channel jumping, the volume cutting out to about 10% of what it should have been, and then back to loud.  I could tell right away that it had awesome tone and that I wanted to keep it and fix it if not too much.  After taking the head out and blowing all the dust out of it, I'm pretty sure thos two issues have been resolved as they have not come back.  Only one problem remains.  The left side speaker cuts in and out making a noticable difference in the volume.  I can plug it into the right side output and it works, but its not as loud a when its on its own left channel.  Its a stereo amp btw.  I have a DVOM, and a decent amount of electrical knowlegde of electronics as I am an automotive tech by trade, we just normally dont mess with circuit boards and stuff like this.  I'm not an electrical engineer, but I'm not and idiot either, so if I could get some guidance on where to start, I'm pretty sure I can fix it.  When I had the head apart I didnt see solder joints that looked too difficult to desolder and resolder if I need to replace parts.  I figure if I can mod an Xbox controller, this should be cake witha little help.... Haha!!

[Enzo]

The first thing to check is the jacks.  And this will relate to the channel jumping and level shifting as well.

Look at all the jacks inside the amp.  Note how when a plug is inserted, it lifts the little metal contacts up.  Note further than there is an additional contact underneath each upper contact, and the lifted contact normally touches the lower contact when there is no plug inserted.   The upper moving contact and hte lower stationary contact act like a switch.  When no plug is inserted, the "switch" is closed.  If this contact gets electrically dirty, the switch doesn;t close reliably.  This causes varioous problems.

Use your meter set for ohms, and measure resistance between the upper and lower contacts when no plug is inserted.  it should measure less than 1/2 an ohm - 0.5 ohm or less.  if it measures higher, the contacts need cleaning or the jack needs replacing.  If the resistance is low, like 1 or 2 ohms, the circuit will work, but that higher resistance is a sign that the contacts are not pristine, and at some later time that 2 ohms will blossom into 2000.

I usually make these readings from the underside, since the next step is to check the solder under there anyway.  I want to avooid presing down on the moving contact, since that affects the contact resistance.  Probing the solder side avoids this.

Check the solder under each jack, and also under each control along the panel.  Also, there are several large rectangular cement power resistors, check the solder under those.

[Safari Jack]

Thanks Enzo!  I did measure some of the jacks from the solder side like you said, just not every single contact point.  I'll take the meter home again tonight and see how that goes.  I may even take my solder iron home and reflow the jacks and the resistors. 

I'm pretty sure that the channel jumping and the level shifting problems are gone though.  The issue now is why is the left side speaker cutting out.  I'll definately check all that other stuff tonight as well though.

[Safari Jack]

Well aparrently either this website is magical, or Enzo is magical, cause last night I played trouble free for about an hour before I was going to open it back up.  Decided not to after it worked so well.  Will keep testing it out though.

[Joe]

One thing that happens a lot is that the leads on some part get corroded, and need to be re-soldered. Sometimes you can pull a capacitor completely out of the board because the corrosion has separated it from the PCB!

[Enzo]

Just putzing around with it may have cured its ills.  Speakers cut out because insert jacks and FX return jacks have intermittant cutout contacts - the very resistances we are checking.  But also some extension speaker jacks have cutouts.  And of course back to parts having cracked solder.

[Safari Jack]

I didn't see any cracked solder the other day, I did check for that.  I'm used to looking for that stuff cause I do light repair on Xbox 360s sometimes.  I'm glad its working now though.  Thanks for the help guys, cause if it starts acting up again I will know where to start.  I love this amp!!