Members NeverTheMachine Posted December 28, 2016 Members Share Posted December 28, 2016 Would like some opinions on what most probably went wrong with my amp. Planning on selling my Mesa Express head that I haven't plugged into in months (maybe a year) so thought I'd give it a test run. It's never had any issues. I turned it on fine, left it on standby for a few minutes to warm up. When I returned the amp was off and it hasn't been turning on since. I checked the fuse and it doesn't look blown to me. The tubes don't look burnt out, but I'm assuming a tube swap out would fix this? Should I replace the fuse as well? Could it be anything else? Thanks,NTM Link to comment Share on other sites More sharing options...
Members SteinbergerHack Posted December 28, 2016 Members Share Posted December 28, 2016 If you have a meter, set it to Ohms (resistance) and test the fuse before going any further. Sometimes they can break loose inside the endcap and you can't easily see it. One test is worth a thousand expert opinions. Link to comment Share on other sites More sharing options...
Members DeepEnd Posted December 28, 2016 Members Share Posted December 28, 2016 ^ If you don't have a meter, a simple continuity tester should work. For that matter, fuses are cheap compared to tubes. You could replace it and not spend much even if it doesn't fix the problem. Assuming it's the fuse, it blew for a reason. Link to comment Share on other sites More sharing options...
Members Mikeo Posted December 29, 2016 Members Share Posted December 29, 2016 Any issues I have had with Mesa amps, have been with the pre amp tube. After you check the fuse, ya just might have a bad tube. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted December 29, 2016 Members Share Posted December 29, 2016 If you find the fuse good, its possible the on off switch has gone bad. It would be the second thing in like to check. Sometimes some contact cleaner and working it a few times can restore operation. You want to use none residue cleaner, not potentiometer cleaner. You work the switch with the amp unplugged then give it a day to evaporate. Dot try the switch with juice still inside the switch. Its pure alcohol which can ignite with a spark and cook the switch. Next I'd pull the tubes and take them down to a radio TV shop that has a tube tester and have them tested. Be sure to number the tubes positions so you can replace them where they belong. Note any of the power tubes having a white film on the inside. If a tube has leaked air inside it will turn the gasses white inside and the tube quickly burns out. If you do find a bad tube testing and its a power tubes you need to replace them in matched pairs or quad sets so the amp runs with a balanced bias. Don't replace them as singles. The preamp tubes can be replaced singly if you find a bad one. If a tube is bad, you're going to want to have the amp inspected to find out why it blew. Tubes rarely just go bad without some symptoms. Power tubes especially need to have their grid resistors checked. Its not a bad idea to have the screen resistors checked too. If the fuse is bad its a symptom of a heavy current draw, usually a dead short. Things like power caps are good for maybe 10 years and need to be replaced. The worst thing you can do is let an amp sit and not power it up on a routine basis. The aluminum oxide barrier in the caps that acts as a dielectric insulator between the plates. When you let the amp sit this oxidation barrier breaks down the cap can develop a short between plates and create a dead short in the power supply. It only needs to be the size of a pin hole to short. Other things to check. Make sure you have a good speaker cord. Never use a guitar cord to connect speakers. Only use a two wire zip cord connector which can handle the wattage. A guitar cord is only rated for a few volts and can melt from the inside out. (#1 cause of noisy microphonic cords too) One thing you should never do is replace the fuse with a higher value. If it blows immediately you have a dead short that needs to be fixed. If the amp does come up after replacing the fuse, leave the amp on standby for a day and allow the caps to rejuvenate. Sometimes the caps are only partially dead and put a heavy drag on the power supply. By having voltage pass the caps the oxide barrier on the plates is restored and the amp may wind up being fine after that. This is about as far as you can go as a non tech. I don't suggest you go poking around inside because there simply isn't anything you can do without formal training in electronics. Besides its dangerous with the high voltages involved. Take it to a pro who has a good reputation and he can not only fix it right the first time, he can probably tell you why it failed in the first place. Link to comment Share on other sites More sharing options...
Members NeverTheMachine Posted January 3, 2018 Author Members Share Posted January 3, 2018 Update: I guess I am close to taking it to a shop having realized I am not the most electronically savvy persons. Tested fuse with meter and it was a go. Then replaced the fuse and the amp turned 'on' but none of the LED lights were glowing on the face of the amp. Furthermore, once I took it off standby, one of the two power tubes would go from the usual orange glow to a dark blueish color towards the base of the tube [what's that about??] I know it's not a cab or speaker cable issue; my peavey C30 head works. Link to comment Share on other sites More sharing options...
Phil O'Keefe Posted January 4, 2018 Share Posted January 4, 2018 A blue glow from a tube is generally nothing to worry about. If they glow bright red, that's a problem. You probably just need to retube it, but to be safe (and since you're not comfortable or experienced with working on electronics), you're probably best off taking it in to a tech and having them check it out. Link to comment Share on other sites More sharing options...
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