My JSX Died - Suggestions?

[shreddermon]

Was plugging into it the other night and, before I could even switch from "standby" to "on", the power light went out. Nothing, nada. The amp is getting power, though, as the channel lights are still functioning and switching fine.

I pulled the back panel, and pulled each tube. They all look OK. They aren't getting any power, though. I also pulled the fuse, which seemed OK, too. When I get a chance to get some spare tubes and fuses, I'll test/replace each one-by-one to confirm they're not the problem.

Anyone have some other good troubleshooting ideas? I want to try everything possible before I have to pack her up and ship it out to an authorized service center. (...The nearest of which is about 85 miles from me. )

[Infernal Death]

Normally i would say that you should disconnect the power transformer from the rest of the psu and see if it deliveres all the right voltages. Look from where the power light gets its voltage. See if the power transformer brings the voltage or if something in the psu section is failing. I never seen the schematic of the JSX but my guess is that the power amp delivers some kind of switching voltage which seems to be ok and maybe the heater voltage is not working (often the power lights are wired to the heater supply voltage). But those are all guesses.

However you need to open up the amp which 1) could break your warranty and 2) wouldn't be a good thing if you don't feel comfortable working with dangerous voltages.

Flo

[shreddermon]

However you need to open up the amp which 1) could break your warranty and 2) wouldn't be a good thing if you don't feel comfortable working with dangerous voltages.

Yep and yep. That sounds like warranty work to me.

[Infernal Death]

Yeah maybe it's better to let a professional look at it. In this case it's always better be safe than sorry

Normally besides changing tubes and fuses there isn't really much you can do without opening the amp.

Since your amp is half-working you definitely would have to check out your working voltages. This brings you to working with a multimeter or even an oscilloscope if you want to trace your signals. Personally i would send in my amp if it's still under warranty. Even if i would feel somehow safe to do minor to moderate repair work.

Flo

[Shawn Lutz]

start with replacing the fuse and tubes, you can't always tell by looking at them if they are good or not

[Spivonious]

Does the amp still sound? It could be just the power light burned out.

[kmanick]

Pat, you really can't tell just by looking at them.
About a week after I got my JSX from Matt, it started sounding like
someone was hitting a bass drum thru my speaker cab evey 30-40
seconds. Completely freaked me out.
All of my tubes were lighting up and they all looked fine.
I bought it back down to Matts and he was nice enough to let me sit
there and swap out each tube one at a time, warm it back up and play
thru it.
I finally found that one of the power tubes was causing it.
I got a fresh set of El34's from Matt and all was and is still Good.
I've got KT-77's in there now and I am loving it even more.
So before you spend the time and moola with a tech I'd get a couple of
fresh power tubes and preamp tubes and start going thru them one at a time.
Let me know what you find
Nick

[dmtnt]

My 2:90 did the same thing, I changed all the tubes out, no difference. From what I'm told it was the transformer.

[Infernal Death]

Yes that's what i think. I am not sure if buying spare tubes and changing them will solve the problem. After all tubes aren't exactly cheap.

Nick, i can see the power tube to be the problem in your case but you got some sound out of your amp. Here it seems like there is some problem with the power. Normally when there is one or more voltages missing it's more of a transformer problem or the psu section.
Maybe it could be that the heater pins of one tube shorted but i never heard of that and i also think if that would happen the amp would have blown a fuse.

shreddermon, just to clarify, there is no sound coming out of your amp ? How about the heaters on your tubes ? Do they glow when the amp is on (but in standby) ? This way it's pretty easy to see if the heater voltage is still working (without having to open the amp).

Flo

[Twisteramps]

Drop the chassis, look inside - I bet it has MORE fuses internally, most peaveys are like that. You may have had a bad tube blow a fuse or something else... but I'd go looking for other fuses before I'd say the transformer was gone or take it to a shop.

Pete

[emperor_black]

My 5150 did the same thing. Took it to a tech and he said the heater circuit had a "cold solder" and the power tubes weren't warming up. I guess you could check if the power tubes are getting heated up or not.

[shreddermon]

To clarify: no sound coming out whatsoever. Dead silence. And the tubes aren't heating up, either.

[Twisteramps]

Again, I'd look for internal fuses. If the tubes aren't heating up, it's not going to work... and you can have the tubes heat up and no sound. There are two main voltages going into the tubes - the B+ and the Heater voltage. Heater voltage is what makes them light up - B+ is what gives you showtime! When you turn your amp on standby, just the heaters are on... when you take it off standby, then the B+ flows and your amp has volume.

You can get a cheapo multimeter at radio shack to test your fuses with. My guess is still an internal fuse blew for whatever reason.

Pete

[jim777]

If it's under warranty this is a no brainer; bring it in and let a pro fix it under warranty. Don't take a chance frying yourself if you're not amp tech inclined yourself.

[shreddermon]

Update: got some spare tubes in, and no change. It's definitely not a bad tube. Gotta track down a fuse as a last check now.

Chances are, though, I'm thinking I've got to ship this puppy off for warranty work. Very bummed.