Amp Problem

[swingtoneman]

I have a small portable 'Roland Acoustic Chorus AC-33' battery / Mains amp. 2 separate inputs--one 1/4" jack, one XLR.

The XLR input has ceased to work. The mic I was using works OK in another amp. Have you come across this problem in other amps? Would you know the cause of one input OK and the other input faulty? Common fault? Remedy?

[darkwaters]

Have you tried spraying the input with electrical contact cleaner?

That’s always been my go to solution for electrical contact issues.( I live on an island in the North Atlantic and oxidation on contacts is an ongoing thing.)

[sgosnell]

It could be a loose wire, or a faulty jack. Hard to say without being able to see inside there.

[nevershouldhavesoldit]

I have a small portable 'Roland Acoustic Chorus AC-33' battery / Mains amp. 2 separate inputs--one 1/4" jack, one XLR.

The XLR input has ceased to work. The mic I was using works OK in another amp. Have you come across this problem in other amps? Would you know the cause of one input OK and the other input faulty? Common fault? Remedy?

The only version of the AC-33 that I know has 2 channels, each with a 1/4" jack. There's also an XLR input on the mic channel. Is it the 1/4" on the mic channel that works, the 1/4" on the guitar channel, or both? Oxidation or other dirt on one or more XLR contacts is a possibility, but I've never encountered a dead XLR jack from that. Most XLR jacks are pretty rugged and failures are few. It's highly unlikely that the contacts in the XLR are the problem, especially in a fresh amplifier that's clean and has the XLR used regularly. It could be the source device or cable - dId you check it with more than one mic? Did you try another cable?

Each channel has its own input stage. So if the XLR doesn't work with any cable and the 1/4" input jack on the mic channel does work, it's likely to be a broken connector in the XLR input or a bad solder joint between the XLR contacts and the board on which jack sits. I don't think there's a separate chip on the XLR input to convert it from balanced to single ended, because Roland labels the XLR pin connections as hot, cold, and ground. If it were a fully balanced input, the correct labeling would be positive, negative, and ground. So I don't think the XLR input pathway is balanced and differential. But if it is, there'd be another chip or an addiitonal small circuit to convert the balanced input to a single ended (2 conductor) signal, and that could be bad too.

[rpjazzguitar]

My recommendation is to consider carefully what Nevershould... said and then consider the following.

Most jack failures IME are due to mechanical stress from plugging in and out. Over time, that can cause a crack in a solder joint. Usually, that's heard as crackling. I'd suggest gently wiggling the jack and pressing on the chassis nearby to see if you get crackling. If you do, the cracked solder hypothesis gets support.

Most likely this jack is soldered right into the board. So, you have to expose the solder connections and reheat them until the solder flows. The soldering is easy. Getting the board exposed is likely to be a hassle. But if you keep unscrewing and unplugging things, sooner or later you'll get there. Don't forget what you did and don't break anything.

Oh, and while you're in there look for loose metal. Sounds crazy, but I've seen it. Like a nut vibrates off and shorts out the jack.

Good luck!