HELP! I busted my friend's MESA!

[gerryluibake]

The amp needs the MOV, otherwise the turn-on pop will be quite severe and will actually kill something.
Transformers are usually quite tough, the fuse should have done its job.

hi if u can see the schematics, the MOV is parallel in the primary winding of the transformer, and the one who supply the components is the secondary winding..and only the MAGNETIC FIELD is the one who transfer voltage from primary to secondary...

as far as i know, mov is just a protection same as fuse..so, with or without these components ur amp still can use...

btw thats just my point of view...cheers...

 

[gsonique]

This is my concern on MOV's ....

Hazards
While a MOV is designed to conduct significant power for very short durations (~8/20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. Under normal utility voltage conditions, this is not a problem. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Application of sustained over-voltage to a MOV can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue.
A series connected thermal fuse is one solution to catastrophic MOV failure. A varistor with internal thermal protection is also available.
There are several issues to be noted regarding behavior of transient voltage surge suppressors (TVSS) incorporating MOVs under over-voltage conditions. Depending on the level of conducted current, dissipated heat may be insufficient to cause failure, but may degrade the MOV device and reduce its life expectancy. If excessive current is conducted by a MOV, it may explode inside the case, keeping the load connected but now without any surge protection. A user may have no indication when the surge suppressor has failed. Under the right conditions of over-voltage and line impedance, it may be possible to cause the MOV to burst into flames, the root cause of many fires and the main reason for NFPA’s concern. Properly designed TVSS devices should contain the flames, eventually resulting in the opening of a safety fuse.

cheers....
Goose

 

[Destructos]

Well one thing for sure is that you do not want to bypass the fuse no matter what, in case the original owner also forgets to use the step down 110v transformer. The fuse most likely saved this amp's life and definitely will again in the near future.

As for MOVs, they are built to work safely at a rated voltage range, like up to 130v in this instance (as quoted in that wiki article: "Under normal utility voltage conditions, this is not a problem."). The term varistor means they will conduct only at very high current, for example the turn-on surge or a lightning strike.
So unless this fella manages to some how draw sustained power of more than 600 watts out of this amp, I don't think the MOV's reliability will be an issue because something else will fail first. Neither do Mesa's Engineers. That's why they put it there in the first place.
Without the MOV, each time Schon or the owner switches on the amp, the turn-on surge will momentarily bring the secondary winding voltages very close to the circuit's capacitor's voltage threshold which will wear them out and shorten the amp's lifespan.

I mean, it's fine if you guys think otherwise, cuz it's not my amp and not my problem. But this isn't Schon's amp either.
So unless it's his, I believe his friend would like to have the amp back as it originally was without missing parts that Mesa Boogie engineers intended to be there.

Schon>> Download and print this out. http://www.schematicx.com/schematic/mesa-boogie-dual-rectifier-schematic/
Take that and the amp head to a reputable electrician in JB, explain what happened and your worries will be over.

 

[dodgethis]

as far as i know, mov is just a protection same as fuse..so, with or without these components ur amp still can use...

btw thats just my point of view...cheers...

Oh yes, the amp can still be used. But the amp is no longer safe to be used if one chooses that path. The point of the damn fuse is to protect an electrical appliance in the event of an overload, surge, etc. You must have almost no knowledge of electrical safety to make such a sweeping statement like that, or just plain ignorant.

You can spend less money and effort replaceing the blown fuse, than re-wiring the whole circuit to bypass the MOV and fuse.

 

[Schon]

Thanx people.. already brought the M to a Tech, explained the problem & asked him to check the MOV & fuse. Will know by 2mrw & hoping for the best. Will update u guys on the outcome..

 

[gerryluibake]

thank you guys,,i learned a lot from all of you...peace...

 

[Schon]

Got d Dual back from d tech. I seems that nothing's wrong with it! What a scare.! Maybe it got a temporary power cut-off when u mistakenly plug it into a wrong wattage. 15 bucks was the damage & I learnt my lesson. From d experience & u guys..
Now for some CHUG..CHUG.. CHUGGING!!

 

[hardcore]

Bro, where did you send it to? who is the tech?

 

[Schon]

Theres a Electronic equiptment repair shop in TMn Sentosa, JB, Advance Electronics. They do repairs for TV, HiFI ect. I think most reputable electrician could do repairs for Guitar Amps, providing u provide the schematics or explain to them, where to check.. Heck, we could also do, ourselves, providing we have the knowledge & the necessary equipment.. & time, of course..

 

[Destructos]

Cool. 15 bucks isn't damage. Just insurance... can never be too sure for a multi-thousand dollar gear like that.

The fuse definitely saved the amps life. I have a yamaha bass preamp that's also fixed at 110v and absentmindedly plugged into 240v mains. For both occasions, a change of fuse was all it took to get it running again.

Time to get those label stickers and write "plug to 110v transformer only!!" and paste right next to the power socket to save yourself from another heart attack. Maybe stick next to the power switch also so that you will always check before switching on. LOL

Have fun. \m/

 

[jmb23]

haha,must write big big or better,

LAMINATE IT!

 

[Schon]

I dont think I d borrow this again,.. hehe. also, after spending a couple of days chugging away,. I feel that a 5150 has more gain, to my liking.. & a reverb.
I know, its a matter of personal preference & taste, but after spending time with those 2 high gain cows, id go 4 d PV...

 

[Destructos]

Oh? That's a cool thought.
Tried switching between tube and solid-state rectifiers?