Help needed troubleshooting a Mesa Boogie 400

[lovechick]

I borrowed a buddy's Mesa Boogie 400 a few months back. Using input 2 and mated with a single 15 SVT cabinet (bass is a MM Stingray), the amp sounded great at moderate volume through a couple of tunes. Then, in the space of about 4 seconds, I lost all sound. I shut the amp down and let it cool briefly. Turned it back on, signal was again present but died after another minute or so. I took the amp to my tech, who made some unspecified, minimal adjustments. I brought the amp to a gig on Friday (with the same cab and bass), ran it for 45 minutes and it sounded great. Brought it out Saturday, made it through 3/4 of the first song and once again lost all sound in about 4 seconds. Any thoughts from other Boogie owners/enthusiasts as to what could be going down? I know this is probably tough to identify with the provided information, but I thought maybe I'm overlooking something or someone had a similar experience with their MB. Thanks.

[RickenBoogie]

Well, the 15 is an 8 ohm cab, so the obvious question is, is the amp set to 8 ohms? If it is, then I'm as stumped as you. Good luck though.

[BassmanPaul]

Take it back to your tech. If it's still faulty he missed something.

Paul

[anderbass]

Something easy you could try yourself: Next time its acting up simply patch/plug a regular guitar cord into the effects Send and Return jacks you'll find on the back panel. If the amp suddenly starts working again your problem is dirty switching contacts in the return jack that probably just need to be cleaned or you could even just leave a short cord in-between the 2 jacks permanently.

[lovechick]

Good call, Anderbass, effects loops can get problematic in a hurry. I'll give that a shot.

[Caca de Kick]

When my two 400's did this, it was the preamp heater circut wire cracked. To verify, I removed the top cover to the head so I could watch the tubes while playing. When the sound cut out, I noticed the preamp tubes were no longet lit up, but the power amp tubes were. Removing the bottom cover you can see the thick solid aluminum wire runs along the side and is soldered to the preamp circut panel, that's were all of mine had cracked solder joints.

[BassmanPaul]

Originally Posted by Caca de Kick

When my two 400's did this, it was the preamp heater circut wire cracked. To verify, I removed the top cover to the head so I could watch the tubes while playing. When the sound cut out, I noticed the preamp tubes were no longet lit up, but the power amp tubes were. Removing the bottom cover you can see the thick solid aluminum wire runs along the side and is soldered to the preamp circut panel, that's were all of mine had cracked solder joints.

Tinned copper is more likely as aluminium is a bear to solder.

Paul

[lovechick]

Thank all. Caca, I was hoping you would have some insight on this. Thank you...

[timv]

Yeah, that wire is a very common problem on 400's and 400+'s. My old one did it a couple times and I helped a fellow talkbasser in canada trouble shoot the same issue by e-mails....
Goodluck....