Princeton Chorus got power, no sound at all

[jaguar123]

Hey everyone. I found a Princeton Chorus amp, power lights all operating lights come on.  But no operating sound at all, no pop when power switch flips. Checked with a cable and guitar that I'm sure of.  Visible speaker connections look fine.  Clean looking amp made in USA black grill, not beat up at all.  Any ideas of what the issue could be, or is this too little information to go on?  Thanks

[Enzo]

Lights up but no sound.  First see if the speaker works.

Pull one or both wires off the speaker, note which one goes where.  Now briefly touch the terminals of a common 9 volt battery to the terminals on the speaker.  A working speaker will pop or thump with each touch.

If the speaker works, then the issue is inside the amp.  And that means taking it apart and using a volt meter.  Are you skilled enough to do that?  Inside there might be simple blown fuses, or it may be failure of some parts.  Can't tell at this point.

[jaguar123]

Hi the speaker wires seem to be pretty solidly attached, will have a better look after work and see about doing the test you're suggesting.  There are two speakers, so can I assume that testing one of them will give me the answer?  Beyond that, the testing with the voltmeter is something I don't know how to do.  Thanks for your help

[phatt]

If this is the model with 2 sets of FX loops then jump them with a cable as they have internal switches which are a common fail mode for nearly all guitar amplifiers.
Even just by inserting and removing a plug a few times can often bring them back to life.
Phil.

[jaguar123]

It does have the two loops.  So by jumping them, do you mean plugging a cable to the in and the out of both those channels?  And then trying to plug my guitar into the main input jack to see if it works?  Thanks for the advice.  Jag

[Enzo]

Some wires may be soldered onto the speaker, but most use a push-on connector crimped to the wires.  Then it is pushed on to the speaker terminals.  Do the wires end in a brass colored thingie that is pushed over the silver colored speaker terminal?  They are stiff, but pull straight off.

The FX loop has a send and a return.  If we plug a cord from the send right into the return, we have done a bypass of the internal loop contacts.  This will not hurt anything.


In fact, you can plug your guitar directly into an FX return and should hear it if the amp works.

[phatt]

It does have the two loops.  So by jumping them, do you mean plugging a cable to the in and the out of both those channels?  And then trying to plug my guitar into the main input jack to see if it works?  Thanks for the advice.  Jag

Yes. :tu:

Enzo is just trying to suss out if the issue is something easy to fix.

And thanks Enzo,, I missed the obvious,, guitar signal into either stereo or mono efx return should send signal through to the poweramp and speakers which would establish that the power amp and speakers are in fact working.
Phil.

[jaguar123]

Tried jumping the fx loops, also plugged into the returns of both channels.  Plugged and unplugged repeatedly.  Total silence.  I'm a bit nervous to try the 9 volt battery to speaker test...but to clarify the process, I unplug one of the wires from the speaker and touch one terminal of the battery to the exposed speaker terminal?  Thanks for the help.

[Enzo]

Pull at least one wire off.  That way we can't send 9v back up into the amp.   Probably wouldn't hurt it, but why take the chance.   Or just pull both wires off.   Then ther are two battery terminals and two speaker terminals.  We touch them together, the idea being to send a 9 volt pulse through the speaker.  You have to touch both battery terminals to both speaker terminals.

Imagine you had a little light bulb in a socket or a little motor, either one wants 9v to run.  We would touch the battery terminals to the terminals of the motor or light socket and the motor would spin or the bulb would light.  Same deal, except we want noise instead of spin or light.

It won;t hurt the speaker.  First in normal operation, the voltage into the speaker goes much higher than 9 volts.  Also, an 8 ohm speaker will try to draw over an ampere from the little battery, the battery cannot supply 1A at 9v, so whenever you are actually touching, the voltage in the battery is dragged down to just a volt or two.  If you held the battery on there it would drain the battery, not harm the speaker.

Besides, it is just a quick touch, like tap tap.  All we want is to hear the speaker make noise or not.  Makes noise, it works, no noise, dead speaker.

[jaguar123]

Thanks Enzo I'll give it a try.  Does the amp need to be on for this to work?  Or does the battery provide that?

[Enzo]

Remember, we disconnected the amp from the speaker for the battery test, so honestly, it doesn't matter a whit whether the amp is on.

[jaguar123]

Right Enzo realized after I posted that was a dumb question.  Did the battery test, speakers work.  Knowing that, what would be the next possible area of defect?

[Enzo]

Your electronics inside is not working, it can be many things.  Start with the power supply.  Are all supply voltages rpesent in the circuits?

[jaguar123]

Hi Enzo, I have no idea...may have reached the point where I need to take it to the shop for further investigation.  But many thanks to everyone for your assistance.  Jag

[Enzo]

Well, if you do not have the basic electronic skills to handle it, yes, you are better off taking to someone for repair.  They will fix it and you will not do it any harm by prodding around.

As a technician, I can say that zero sound is usually easier to sort out that half-assed sound or some distortion.  it could be a lot of things, but your amp is not blowing fuses, so that is a sign the expensive stuff is likely OK.   Both channels are affected, both speakers, so it would likely be something they share in common, first on the list is power supply. 

It is also possible, getting ANY sound back reveals a more serious problem.  I don;t know for example if inside someone had disconnected something that made the speakers dead, but was done for a serious problem.  Just discuss it with your repair man.