marshall DBS 7400, need help

belgamrood · #1 05-30-2012, 08:16 AM

hi there

i have a DBS 7400 rig, the head and two DBS 2X10 cabs

lately i have some issues with it

after 10 minutes of playing it shuts down? the power indicator is still burning but theres no sound
if i turn the volume up, at some point ( different every time) theres a loud "bop" and then the sound comes back
after some time, 10-15min, same thing all over again

i checked if it gets too hot, thats not the case

is this a known issue with this amps? i did a bit of research but couldnt find anything

had it checked by local amp tech, he claimed to have fixed it
he chainged the master vol pot and the preamp tube, and cleaned it
when i got it fixed there, i played it for about half an hour and no problems.
next day rehearsal with the band, problems start

any help at all would be very welcome

thanx

belgamrood · #2 05-30-2012, 11:01 AM

anyone?

RickenBoogie · #3 05-30-2012, 05:33 PM

You need to take it in to an amp tech. Impossible to diagnois over internet. Besides, the tech will have the testing equipment needed.

Gopherbassist · #4 05-30-2012, 05:36 PM

Welcome to the forum! Can't say I have any experience with the problem you're having with the amp, but maybe check the fuse and make sure it's in working order. I can't imagine how they'd do it, but if someone jury rigged an old fuse to work after it had blown, or just stuck some random piece of metal in, that might be causing the amp to lose power.

Also, you might get a power controller. If you're not getting consistent power from the wall the amp will let you know it.

belgamrood · #5 05-30-2012, 05:43 PM

Quote:

Originally Posted by Gopherbassist

Welcome to the forum! Can't say I have any experience with the problem you're having with the amp, but maybe check the fuse and make sure it's in working order. I can't imagine how they'd do it, but if someone jury rigged an old fuse to work after it had blown, or just stuck some random piece of metal in, that might be causing the amp to lose power.

Also, you might get a power controller. If you're not getting consistent power from the wall the amp will let you know it.

whats a power controller?

belgamrood · #6 05-30-2012, 05:45 PM

Quote:

Originally Posted by RickenBoogie

You need to take it in to an amp tech. Impossible to diagnois over internet. Besides, the tech will have the testing equipment needed.

sadly, theres only one tech that i know of here in my neighbourhood, and he didnt seem to fix it...

i even tried contacting marshall about it, may take some time though before they react..

Gopherbassist · #7 05-31-2012, 02:13 PM

A power controller is a typo. What I meant was a power conditioner. This is a device that keeps the voltage coming from your wall outlet constant instead of letting it fluctuate.

B-string · #8 05-31-2012, 02:29 PM

Have you tried and instrument cable between the effects send and effects return jacks yet?

belgamrood · #9 06-09-2012, 10:45 AM

tried the effects loop thingy, still keeps shutting down...

B-string · #10 06-09-2012, 11:19 AM

Sounds like a cold solder joint in there somewhere then or a failing opamp.

Humbucker3 · #11 01-05-2013, 11:16 PM

I bought mine new in 1994. It looked great and sounded great. Then it crashed and was not gig worthy in a short amount of time.

I took it to a few amp shops with dismal results. It crapped out on gigs!
Living in the music capital of the world- LA, CA -USA-I searched for the ultimate amp repair guru and it wasn't ez.

I finally found brainiac Robert Dixon in Burbank CA, that owns the AMPHOLE.

RD was working on amps for Keith Richards, Red Hot Chili Peppers etc, and had an intense knowledge of all amps with vintage amps like no other tech.

Here is your answer as my DBS 7400 was fixed and I played 60 gigs with it after RD started working on it.

Let me tell you the basic faults on this rig.

Cheap alloy jacks and inputs that just invite Corrosion. Thus no signal. He replaced some inputs and jacks with the stuff used on the old Marshall. New parts but high quality. Then he just frowned at the cheap PC board and solder connections inside. One knock and your PC board and a solder connection is kaput. He re-einforced those main connections.

An effects loop had heavy corrosion -thus no signal. And my amp was pretty new! Cheap factory parts.

RD explained the old reliable amps had "point to point' wiring vs the cheap PC boards that have been used for the last few decades on all amps. P to P wiring like in the old Fender Amps from the 60's etc, would just be too expensive to manufacture today. Thus cheap PC boards in the amp head.
Wiring was so much stronger. So that is the answer. Talk to your tech about this, but he has to be a super pro tech with tons of experience like Robert Dixon. I am a pro bassist.