Mesa Boogie Mark II C+ Blowing fuses???

[neale dunham]

Hi People! I own the Mesa Mark II c+ (non Eq) Last night i turned up to a gig and plugged in as usual.... Then i noticed that the amp light had gone out. I reached around the back of my Power conditioner and found the amp lead not quite pushed in square. So i hammered it home and the orange light flickered and went straight out again. On further inspection i had blown the main fuse. I changed the fuse and hey presto... same again! I cannot work out what the problem is?? Can any one help me fault find this? Thanks.

 

[Boogiebabies]

Try new power tubes.

 

[neale dunham]

Thanks for the reply..Did that? Put new fuse in... blew it to pieces! What could i try next?

 

[Boogiebabies]

You may have a blown or disconnected filter cap. It's time to pull the chassis and take a good clear picture.

 

[stomper]

http://geofex.com/ampdbug/ampdebug.htm

 

[Boogiebabies]

I was wondering if it is blowing the fuse on powering up, or when you go off standby ?

 

[neale dunham]

It Blows the fuse on power on? I cant even get to the standby?? thx.

 

[Boogiebabies]

What position do you have your ground switch ?

 

[jvk]

Hi Ed and Neale

Besides the cap it could be that the varistor blew and is shorted somehow (they're supposed to fail open circuit), because there was a spike caused by moving the plug around.

Did you replace the fuse with the right rating?

 

[Boogieman]

To echo jvk's post: always replace the fuse with the correct value specified on the back panel. If your amp has the international voltage selector, the fuse value should correspond to the one specified for your local voltage.

More than 20 years ago, some droid at a music store suggested I put a higher value fuse into my amp that kept blowing fuse, and I was dumb enough to heed his advice. Well, there was no explosion, just a puff of smoke with the smell that something was burnt. It was bad filter cap that caused the fuse blowouts, but the higher value fuse blowout also took out the tranny.

The tranny replacement was expensive (IIRC, parts and labour came to about US$180 at the time), but at least they were readily available from Mesa back then.

 

[jvk]

I bought a Boogie once for peanuts because the owner thought the PT was blown. He even took it to a tech who told him he'll need a new PT. I checked the PT and sure enough it was blowing fuses all the time, but was testing normally with a meter. So I figured out that he was using 1A fuses instead of 3.15A (as recommended), and they would blow right away. Poor guy. Suffice to say that I made a good profit when I sold it

 

[Restless Rocks]

Let's not overlook the possibility of a shorted rectifier diode. A real fuse blower for sure and could lead to tranny damage with an oversized fuse.