Little Mark III has gone quiet. HELP

MUSHROOMSeAcOw · #1 08-04-2011, 07:35 PM

I just played through my week-old Markbass rig, and suddenly it has no power. There is sound, but it's maybe 5w at most. The master volume does nothing but silence it, and the gain only boosts it a tiny bit. Yesterday it was rattling the windows across the house, today I can't hear 5 feet away. I checked all of the connections and controls. The fan seems to be working. I still get the subtle tweeter hiss that tells me that it's on, but there is almost no volume. I'm kind of panicking, because this is a used head from the classifieds and I don't have a backup amp. Yes, I've tried multiple basses and checked their volume. I took all of my effects out and just ran directly into the amp, same result. I shut it off and back on several times. I swapped the fuses out while I was checking them. I really do not know what's going on. ANY help is greatly appreciated. Thanks in advance.

**JxBass** · #2 08-04-2011, 07:45 PM

Try plugging your bass into the Effects Return. If you get decent output with the Master Volume it points to the preamp stage.

erock138 · #3 08-04-2011, 07:47 PM

+1. If it has a tube pre amp, i'd check/replace that accordingly. Side note, I had a similar problem with my eden head, and it turns out that it was the voltage regulator in the power section, if it's not your pre.

GrowlerBox · #4 08-04-2011, 08:00 PM

If it's a week old, does it matter? Just take it back and get another. They're generally reliable, and it's unfortunate that you seem to have picked up a failed unit.

Edit: Sorry -- just saw the bit about the classifieds; i.e. it's not a week old. Plugging in to the effects return is a good idea, although I believe the LMIII has the same circuit as my F1, which is to say that the effects loop doesn't bypass the preamp. There is no tube. If the master doesn't even increase the hiss level, it sounds like the issue may be in the power section. You need a technician.

It's worth emailing Markbass -- their CS gets a bit of a bad rap on TB, but I have had quick and helpful responses to any of my queries, also regarding a second hand head.

**B-string** · #5 08-04-2011, 08:02 PM

Quote:

Originally Posted by GrowlerBox

If it's a week old, does it matter? Just take it back and get another. They're generally reliable, and it's unfortunate that you seem to have picked up a failed unit.

Did you fail to read that it is a used unit from the classifieds?

**JxBass** · #6 08-04-2011, 08:10 PM

Quote:

Originally Posted by erock138

+1. If it has a tube pre amp, i'd check/replace that accordingly. Side note, I had a similar problem with my eden head, and it turns out that it was the voltage regulator in the power section, if it's not your pre.

It's a solid state preamp so unfortunately it wouldn't be a simple tube swap if the problem points to the preamp section.

GrowlerBox · #7 08-04-2011, 08:11 PM

Quote:

Originally Posted by B-string

Did you fail to read that it is a used unit from the classifieds?

Yes I did, initially -- I was typing my edit while you typed this, I guess.

**B-string** · #8 08-04-2011, 08:19 PM

Try looping a cable from the effects sent to effects return and see if you have volume.

ErnieD · #9 08-04-2011, 11:32 PM

not sure if the III suffers from this but, what type of speaker cable are you using? If its a speakon style connector, try it with a regular 1/4" connector speaker cable to back of amp. I had a sort of shorting out when I used a off-brand speakon connector cable with my LMII.

When I switched over to a 1/4" connector speaker cable, problem was solved. I noticed that if I moved the speakon connector cable abit with my finger it would work fine but then start cutting out, like a short. Just something I came across with my MB LMII, may or may not help. Good luck, let us know what the fix was/is.

Russell L · #10 08-05-2011, 06:16 AM

I had that happen with my Fender Bassman 150. Sometimes it would come on fully powered with sound, sometimes at only a fraction of the sound. One day, when it worked, I was messing around in the back of it, trying to get the headphone jack to work also. I unhooked the speaker from the amp. The thing has worked every time ever since. I wonder if it was someting about the speaker jack, dust or other debris on it causing it to short out. I dunno. But, maybe unplugging the speaker and plugging it back in will help. Worth a try. (Oh, and I never got the headphone jack to work, dunno what's wrong with it).

BassmanPaul · #11 08-05-2011, 10:27 AM

Quote:

Originally Posted by erock138

+1. If it has a tube pre amp, i'd check/replace that accordingly. Side note, I had a similar problem with my eden head, and it turns out that it was the voltage regulator in the power section, if it's not your pre.

Mark Bass uses a wired in tube that is not replaceable.

BassmanPaul · #12 08-05-2011, 10:28 AM

As always the first question is what speaker cabinet(s) were you using??

**B-string** · #13 08-05-2011, 09:25 PM

Quote:

Originally Posted by BassmanPaul

Mark Bass uses a wired in tube that is not replaceable.

WHAT THE H E double hockey sticks were they thinking!!!!!

**JxBass** · #14 08-06-2011, 03:53 AM

Quote:

Originally Posted by B-string

WHAT THE H E double hockey sticks were they thinking!!!!!

I believe it's a little mini-tube and not a standard socket-sized tube. And I could be wrong but I thought that it was just in the LM Tube and LM Tube 800, not in the LMII/LMIII.

BassmanPaul · #15 08-06-2011, 11:07 AM

Quote:

Originally Posted by B-string

WHAT THE H E double hockey sticks were they thinking!!!!!

The tube has a life span longer than the amp itself.

BassmanPaul · #16 08-06-2011, 11:10 AM

I repeat my question: what cabinet(s) were connected to the amp???

**B-string** · #17 08-06-2011, 11:21 AM

Quote:

Originally Posted by BassmanPaul

The tube has a life span longer than the amp itself.

.................

Bassmec · #18 08-06-2011, 12:04 PM

Quote:

Originally Posted by B-string

.................

There was a time, long ago that we used lead solder to fit these things.
What do markbass do surface mount them?.
The bloke that turned up in the rehearsal studio with an all new
1 X 12 300 watt combo (says 500 watts but its an 8 ohm speaker so not true), anyway he wont have his long as it sounded as if he drove it to X Lim a good few times.
With a sound like braaappp! on one note. or something quite similar.

BassmanPaul · #19 08-06-2011, 12:51 PM

Quote:

Originally Posted by Bassmec

There was a time, long ago that we used lead solder to fit these things.

When I was doing my apprenticeship in my teens I had to swap this king of tube in and out of circuit assemblies known as toggles. These were for early telephone subscriber trunk dialling racks that I was commissioning. The tube that Mark Bass uses is a pentode.