The first thing I'd try is opening the chassis, look at the loop jacks while plugging a jack in and pulling it out.
Switching jacks can sometimes be bent wrong and may just need to be bent into the correct alignment.
Some switching jacks are enclosed in a plastic tube, if so, you won't be able to bend anything back into place.
Replacing the send and return jacks should be easy to do.
As was suggested, please post close up pics of the loop jacks and the footswitch jacks.
Re: Crab Amp Broke
Posted: Sat Jun 14, 2025 6:31 pm
by linthat22
I'll get on the pictures gents, just probably not today. I'm trying to keep our one hound off his feet since he's been gnawing on them due to allergies. Poor fella is limping. I decided to set some time aside tomorrow and I'll get some gut shots. I'm sure I'll find broken glass in there too lol
*Edit - So the pup's paw is still swollen and needs monitoring. I should be able to provide pictures come Tuesday barring any heart disease issues or issues with the hound's paw.
Re: Crab Amp Broke
Posted: Mon Jun 16, 2025 7:15 pm
by linthat22
Alright guys, here she is. I think the fx loop I bought might omit the foot switch lol
Re: Crab Amp Broke
Posted: Mon Jun 16, 2025 7:34 pm
by linthat22
I grabbed my multimeter and tested for continuity on the board that houses the foot switch and FX Loop and I get a beep when I touch the closest pin to the chassis on all three. I then traced the wires and get a beep on those as well.
Also uploaded a clip with my potato.
Re: Crab Amp Broke
Posted: Mon Jun 16, 2025 8:13 pm
by heath
The pin closest to the chassis is going to be the sleeve connection point and it should go to the common ground (which is why you are getting continuity there). The middle one is the ring, and the third closest is the tip. If you plug in a patch cable and check between the third closest to the chassis you should get continuity. Honestly, depending on how closely they cloned the Mark II and Mark III, it should get continuity when nothing is plugged in as well. The effects loop in the original amp was just two switched jacks that when nothing was plugged in bridged the two jack's tip connection.
It's difficult to tell without looking at the solder side of the board, but it could be a cold solder joint on the jacks or a defective jack. If the builder decided to get fancy and add a relay for the FX loop switching or something like that, it could be that as well.
I would also check to see (with nothing in the fx loop) if the third closest terminal has continuity to ground (closest to the chassis) on either the send or return jacks. If they do that would be why the signal is gone when the loop is empty. It would point to maybe a faulty jack or shorted solder joint or something along those lines.
Re: Crab Amp Broke
Posted: Mon Jun 16, 2025 8:47 pm
by I'MAPUNKROCKERDAMNIT
I've had two jacks, like those, fail... RIGHT OUT OF THE BOX on brand new pedals... one on a Cry Baby Bass Wah and one on a Behringer Chorus Pedal.
The wah wouldn't let me put the guitar cable in.
The Chorus Pedal wouldn't take any signal but, if I used jumper/test cables to bypass the socket, it worked.
I know they're everywhere but, I'm not too fond of those jacks.
Cool guitar!!! It looks like it was made for sitting down!!!
Re: Crab Amp Broke
Posted: Mon Jun 16, 2025 9:02 pm
by linthat22
heath wrote: ↑Mon Jun 16, 2025 8:13 pm
The pin closest to the chassis is going to be the sleeve connection point and it should go to the common ground (which is why you are getting continuity there). The middle one is the ring, and the third closest is the tip. If you plug in a patch cable and check between the third closest to the chassis you should get continuity. Honestly, depending on how closely they cloned the Mark II and Mark III, it should get continuity when nothing is plugged in as well. The effects loop in the original amp was just two switched jacks that when nothing was plugged in bridged the two jack's tip connection.
It's difficult to tell without looking at the solder side of the board, but it could be a cold solder joint on the jacks or a defective jack. If the builder decided to get fancy and add a relay for the FX loop switching or something like that, it could be that as well.
I would also check to see (with nothing in the fx loop) if the third closest terminal has continuity to ground (closest to the chassis) on either the send or return jacks. If they do that would be why the signal is gone when the loop is empty. It would point to maybe a faulty jack or shorted solder joint or something along those lines.
Lots of great info here. I appreciate the areas to look and test. When I remove her from the shell, I'll give it a shot
Re: Crab Amp Broke
Posted: Mon Jun 16, 2025 9:04 pm
by linthat22
I'MAPUNKROCKERDAMNIT wrote: ↑Mon Jun 16, 2025 8:47 pm
I've had two jacks, like those, fail... RIGHT OUT OF THE BOX on brand new pedals... one on a Cry Baby Bass Wah and one on a Behringer Chorus Pedal.
The wah wouldn't let me put the guitar cable in.
The Chorus Pedal wouldn't take any signal but, if I used jumper/test cables to bypass the socket, it worked.
I know they're everywhere but, I'm not too fond of those jacks.
Cool guitar!!! It looks like it was made for sitting down!!!
Thank you dude, I guess those jacks are quite temperamental. I'll keep an eye on those along with the previous gent giving test points.
And yeah, I didn't feel like throwing on a strap, so I just sat her down. It sits great though whether sitting or standing.
Re: Crab Amp Broke
Posted: Tue Jun 17, 2025 2:55 pm
by fastredponycar
My jubilee has the EXACT same problem. I have to keep a little patch cable connecting the send/return jacks if I'm not using anything in the loop.
No idea what caused it and too lazy to take it to a tech. The amp still makes sound when the patch cable is removed but it's much quieter and sort of cuts in and out randomly. Attach the patch cable and it's 100% perfect
Re: Crab Amp Broke
Posted: Tue Jun 17, 2025 10:56 pm
by linthat22
fastredponycar wrote: ↑Tue Jun 17, 2025 2:55 pm
My jubilee has the EXACT same problem. I have to keep a little patch cable connecting the send/return jacks if I'm not using anything in the loop.
No idea what caused it and too lazy to take it to a tech. The amp still makes sound when the patch cable is removed but it's much quieter and sort of cuts in and out randomly. Attach the patch cable and it's 100% perfect
I guess it's a good thing that amp makers/designers use the loop as a quick troubleshooting test to narrow down the problem. Doesn't make it any less frustrating, but it is something learned
