#1
K well, I've come up with nothing, so hopefully you guys will.

One of my modded VJs kicked the bucket the other day. The tubes are fine, transformers are fine, output jacks are fine. It's powering up, but no sound from any of the cabs I've tried with it.

It has been sitting it the exact same place for 4 months. The other day I turned it on, played for less than 5 minutes, then it started cutting in and out, and now I just get no sound.

Please don't say "try new guitar, change tubes, change leads, change speaker cabinet" as I have done these. I REALLY don't wanna go through every connection in the damn thing, so hopefully someone has had a similar experience and can give me some other sections to check.

This amp means a lot to me. First tube amp I paid for on my own, first tubes I changed on my own, first 240 volt shock. I love her!

(It also needs to be said that I can't remember if it has a bleeder resistor or not, and I can't discharge the caps myself tonight)
Quote by kyrreca
If your EQ looks like this your audience will look like this
#3
yes. tubes are fine. everything is powering up. just no signal to be found. As I've said, I've also tried new tubes.
Quote by kyrreca
If your EQ looks like this your audience will look like this
#4
Time to bust out the multimeter perhaps.. there aren't that many connections in a VJ. Be happy it's not a Mesa Roadking or something. Also, how do you know the tranny is fine?
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

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Rackmount Tube Amp Project <<< Updates!
#5
because EVERYTHING is getting power, there is just no signal getting to the speakers. There is a lot of things in the signal chain that could be screwing it over, which is why I really don't want to do it. I have about an hour of natural light in which to do these things, so I'm looking for advice on what common faults cause this, and where to check
Quote by kyrreca
If your EQ looks like this your audience will look like this
#6
Well, I don't know that much about amps and the way they (mal)function. But what I would do first is check the power supply caps and diodes. Perhaps the power supply on the filament side works fine but it's botched on the anode supply? And just look around for any obvious signs of burnt resistors/caps/leads, which is pretty obvious..
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

Bugera Users Militia. We are horrible people. With a sprinkler fetish.
~ BUM: For all things extinguishing

Rackmount Tube Amp Project <<< Updates!
#7
The most common things would be blown output transformer, bad solder joint, liften/broken copper trace on the board. Burnt resistor or bad cap through your bias off and either starving the tubes or causing the tubes to be pushed into cutoff. A wire that is supposed could be shorting to ground. If any of the coupling caps have gone bad it'll do it. Because you have modded the thing that makes trouble shooting even more difficult.

To start off I would suggest you open and look around inside for loose wires, burnt parts, broken wires, and loose wires. If anything doesn't look right then fix that. If it's still not working power up the amp, dim the lights (but don't make it so the room is dark) and start poking stuff with a wooden chopstick. There is a good chance the offending part will either arch (you will see blue light) or make a loud thumping noise when you tap it. If lots of parts make a loud thumping noise then chances are it's whatever part was making the loudest thump.

If you can't find it that way you are going to have to break out the multimeter and start checking connections that way.
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#8
Quote by Cofflecakes
K well, I've come up with nothing, so hopefully you guys will.

One of my modded VJs kicked the bucket the other day. The tubes are fine, transformers are fine, output jacks are fine. It's powering up, but no sound from any of the cabs I've tried with it.
You know more than you are saying. What mods have you done? I'd consider them more suspect than the stock portions of the circuit.

Quote by Cofflecakes
Please don't say "try new guitar, change tubes, change leads, change speaker cabinet" as I have done these. I REALLY don't wanna go through every connection in the damn thing, so hopefully someone has had a similar experience and can give me some other sections to check.
There are tons of things that can go wrong with an amp to give you no sound. And just going through all the connections won't necessarily find the problem. If a resistor opened internally, the external connections will still look fine. You've changed the guitar lead, but if this is a head, what about the speaker lead? Did you change that too?

Quote by Cofflecakes
It has been sitting it the exact same place for 4 months. The other day I turned it on, played for less than 5 minutes, then it started cutting in and out, and now I just get no sound.
No sound as in not even the slightest hint of hum or noise from the speaker? I'd be suspicious of the output jack first. Then perhaps the B+ supply.

Quote by Cofflecakes
(It also needs to be said that I can't remember if it has a bleeder resistor or not, and I can't discharge the caps myself tonight)
Easy enough to figure out. Is this the Version 1 combo? No bleeder. Versions 2 and 3 have bleeders. Don't know which Version yours is? Post #2 of this thread has the information for identifying which version you have: the Epiphone Valve Junior Resource thread
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#9
Cheers guys.

I've tried different speaker cables also. It's a head and my problems with the mods is that 3 different people have worked on it, so it's hard to know who has added and who has removed what. I always made a point of discharging caps no matter what before I did anything.

I get a tiny bit of hum into the speakers, but I never really got much anyway, its always been deadly quite for me.

It's been unplugged for 24 hours, so now I feel comfortable poking around to check all the loose wires and joints. I'll have a quick look for solder joints, but I only have about 45 minutes light left.
Quote by kyrreca
If your EQ looks like this your audience will look like this
#10
I recommend going through it with a multimeter. Start in the middle, check to make sure voltages are correct. Here's where an oscilloscope comes in handy. I know not everyone has the luxury, but if you can borrow one for a few hours, it may help.