OK, so there is something wrong with my amp. As soon as i take it off standby the amp dies and the fuse is taken out. I thought it might be the power tubes so i got new ones, put them in, fired it up and the same thing is happening... i'm really frustrated with this thing. I can't really afford to send this thing down to california again to have it looked at (i sent it down to Mesa about 3 years ago to get it fixed for a different problem). Any ideas??
Mark III keeps blowing fuses
- Thread starter rgx612a
- Start date
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brion
Well-known member
Did you replace the fuse and fire it up with all power tubes removed? If not, check it's behaviour in that state and report back.
brion
Well-known member
The screen grid resistors on the 6L6 inner pair go from pin4 to a Terminal strip bolted to the Chassis They should read 470 Ohms and be rated for 3Watts. Careful in there. If you don't know how to safely discharge the caps, the amp can hurt or kill you.
rgx612a said:
It could also be the rectifier diodes (or bridge rectifier). thats what happened not long ago in one of my Marshalls. Take out all the tubes, to test it. If the fuse blows again, it may be the rectifier or some bad filter cap. You can test the caps with the ohm-meter but be **** CAREFUL, they can kill you or at least your ohm meter. Discarge them first! They should not read zero.
brion
Well-known member
Check out this link and do a google search for videos and other tutorials.
http://www.justinholton.com/hotrod/caps_p.html
http://www.justinholton.com/hotrod/caps_p.html
I drain the caps with some wire I made myself with clips on each side and a 1K 10W resistor in between. One end grounded, one on the caps plus. Check with the multimeter afterwards. It should read a few milivolt max.rgx612a said:
you can measure the screen resistors, but I dont think they are the problem.
megavoice
Well-known member
Hi,
please check the power-cable and especially the power-connector carefully.
Just had the same prablem for many years 'till I detected that the cable had been broken very close to the connector.
The original connectors are crap.
Cheers
please check the power-cable and especially the power-connector carefully.
Just had the same prablem for many years 'till I detected that the cable had been broken very close to the connector.
The original connectors are crap.
Cheers
I'd remove the amp from the shell/combo chassis and look for loose items shorting against anything. Pick it up and shake it. Take compressed air to it (make sure you have a water filter on it if using a compressor) and blow the crap out of it. If you find nothing, it's time to take this to a professional.
kdorsey said:
This solution is probably your best bet. I know it sucks if you depend on that single amp alone, but ask yourself this, can you afford NOT to send it to a professional or Mesa Boogie...I know, not the insight you want to hear/read...
Try removing all the tubes including the little preamp tubes. Could be the fan or fan cable. I'm also leaning towards a shorted rectifier diode or power supply capacitor which, if you don't have skills or a meter, I would recommend taking it to a mesa repair shop. bummer, I know.
- Pat.
bummer, I know.- Pat.
megavoice
Well-known member
rgx612a
Excuse me please, I was in a hurry and didn't read carfully. Of course, mine had nothing to do with "stand-by" and "power on", but I wish you the best to get your amp fixed. If nobody can help you here, I'd advise you to send you amp to Mesa if you love it - even if it's expensive.
Cheers
Excuse me please, I was in a hurry and didn't read carfully. Of course, mine had nothing to do with "stand-by" and "power on", but I wish you the best to get your amp fixed. If nobody can help you here, I'd advise you to send you amp to Mesa if you love it - even if it's expensive.
Cheers
