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GK MB115 problems (please help)

M

meinl

May 19, 2009
143
1
Anoka, Mn ( N of twin cities)
#1
Hey guys,
I have been raising money to get gear for an orphanage in Honduras. So the gear I was able to get was awesome. For instance I got like a $3000 drum kit for $400!!! Anyways I got a GK MB115 for a bass amp.

After I got it I played with it for a couple hours. The tone was good and it was nice and loud. I was very very impressed with it and the tone. I got it because I could fly with it, because it was only 35 lb's and still had some umphh.

I had a slight problem when I found out the airline said they will charge for any boxes over 62" linear inches. The box it came in was 67". the box did not protect it very much either I don't think. So I made cardboard corners from the box, put a hard card board over the grill, put bubble wrap all around, and then put a ton of the plastic moving stuff. I did a really good job on this... there was no way I would let ths guy get damaged.

So I flew to Honduras yesterday and the moment of truth came when I took the amp out of the packing... it was unscathed and in perfect condition! well cosmetically that is.
Now when I plugged in... well it must have had something go wrong :-(

There is no volume when turned on if you turn everything at halfway which at my house in the states was really loud there is a treble quiet sound. So you can somewhat hear the bass, but it is in no way like it should be. Every once in a while the bass noise will fart out. It is still not as loud as it should be and it is distorted. Is it a loose wire? The headphone jack doesn't have output either. I know the bass and the 1/4 cables work I have tested them this morning with the guitar amp I brought.

So if anybody has any ideas. I opened it up and circitry appears to be good although whoever did the glue type stuff didn't do the best job.
So thanks for the help guys :-) :bassist:
shalom,
matthias
 
#2
Everything that's connected with a plug inside the amp, unplug it and plug it back in. You might get lucky.

If that doesn't work, then you've probably got a bad solder joint somewhere. They're usually easy to find, but if you don't have a soldering iron and/or you're not skilled in this area, then the point is moot.
 
#3
trying to figure out how to load the photo... my computer isn't wanting to uplod it apperently....

This is the one area that looks sketchy. The white stuff (some sort of glue maybe??) This is the one area whee the outside is not solid and it rubs off on your finger.... So really not sure....


Also I cannot seem to find a fuse anywhere!....:confused:
 
#5
there is one up at the orphanage which is a two hour drive up a mountain road. Right now I have some things I need to do in the city though...


It just kinda miffs me that this happened.... but these things happen so.

Just where is the fuse in this guy? I don't see anything that looks like a fuse (or atleast from what I have known fuses to look like) anywhere... does anyone have a pic of the inside of one. Or if you know what it is supposed to llok like on the inside I can email ou some pics of this guy. I would upload them, but TalkBass isn't uploading them there is some sort of error.
 
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#6
A fuse is not the problem, if it were, the amp would not come on at all..... when a fuse blows, it breaks the circuit completely..... I think you are not getting enough voltage for the amp to work properly, I have had it happen to me and my amp sounded just like what you have described.....
 
#9
If that white stuff rubs off on your finger like a sort of white grime, it sounds like heat-transfer compound, not the silicone goo they use for component support/damping.

If you still can't get pics to upload, put them out at Photobucket and just link to them.
 
#10
Having done some Googling, mains is 110V 60Hz. Amp is a Class D output with a SMPS. At least I assume the power supply is so, the manual states it has a Class D ouput stage and power supply.

In my mind the amp should work fine in Honduras. The output may be down a tad but I would have though the SMPS should be able to compensate for that slight a mismatch.

I would disconnect the speaker from the amp and test it with a 9V battery. It should give a hearty thump and the cone visibly move. If it does then the problem lies with the amp. No thump and the speaker may well be damaged.
 
#12
I'm no expert at all, but is it possible something happened in transit like temperature extremes?

Weird residue, possibly a capacitor burst?

capblown_6.jpg
 
#14
That area you showed is the temp sensor tie-wrapped to the top of that coil, with heat-transfer compound connecting the two thermally. My MB200 has the identical setup and is a trouble spot. Details are in the huge MB200 thread. At first I thought the problem I was experiencing was a speaker-jack problem, then thought it was a fan problem, but it turned out to be either a bad solder joint at the coil itself or the coil wire is broken down at the PCB. I don't have time to do a proper exam+fix on it, so what I did was create a 1"x1" shim out of several layers of electrical tape and shoved it between the coil and (what I assume is) the transformer next to it marked TC-733 etc, just thick enough to put VERY SLIGHT side pressure on the coil, and that's kept the amp running under every condition I've been able to throw at it. As I said, full details in the big MB200 thread. Little chance your MB200's problem is the same as mine but you've got nothing to lose by trying my temporary fix. Worst that can happen is you'll have to pull the shim because it didn't help.
 
#15
Hey guys its still isn't fixed, but the problem is definately being narrowed down...

Hey Craig thanks for the info... I definately understand it better now. The fix didn't quite fix anything.


ok the schematic says things go in this order
bass>1/4 cable>input (a or p)>direct out>gain>contour>4 band eq>boost>aux in>master>limiter>amp> tweeter>speaker

ok the bass works. The 1/4 works. I have problem still persists no matter which input is used so it must not be that. I don't havea balanced cable at the moment to test if the signal is still good at the direct out. the 4 band eq seems to work. The tweeter swich works. The limiter works from what I can tell. I tested the speakers with another amp and they work fine... the tweeter has a really big hiss... I was reading another post where someone talked about this and said it wasn't the tweeter... well it is.. not sure what is up with them, but their hiss is loud compared to the signal volume... but with the tweeter mute that hiss goes away... in this amp it sounds better with out it. In my main amp I use in the States it has a tweeter and I like the sound, but that one doesn't hiss like crazy....

I also plugged a cd player into the aux in and it works nice and loud... doesn't sound that great, but hey its a bass amp and not a nice speaker system :D

So the problem is somewhere after the inputs and before aux in.


So I don't know if this helps you guys determine the cause wether it is the boost, the eq ( I don't think it is) the gain, or the contour. I am guessing it is either the gain or the boost.

Thanks guys so muchfor the help we are almost there.. by the way I am really surprised by the weight of the whole amplifier unit in this combo.. on its own the amp only weights maybe like 3lbs? its light...

shalom,
Matthias
 
#16
craig.p said:
Everything that's connected with a plug inside the amp, unplug it and plug it back in. You might get lucky.

If that doesn't work, then you've probably got a bad solder joint somewhere. They're usually easy to find, but if you don't have a soldering iron and/or you're not skilled in this area, then the point is moot.
Click to expand...

Wouldn't that void the warranty anyway? Or is this too far away to even consider shipping to and fro?
 
#18
Have you tried removing and then reinstalling every connector cable inside that amp? Same deal as the other suggestion I made: long shot, but worth a try anyway. Apologies in advance if you said you already tried this and I missed it.

Something else you can try is to plug a bass into the amp and play while you use something non-metallic to press VERY LIGHTLY on various components, to see if the sound suddenly comes back. A chopstick works well but really you can use almost anything reasonable: the back end of a plastic disposable ballpoint pen, for example. Again, this is to check for a bad solder connection. I'm going on the theory that there was physical damage related to shipping, even though the packaging showed no evidence of it.
 
#19
ok I will try that I will let you know how it goes :-)

hopefully :smug::rolleyes:

its actually been kinda fun to learn about the amp :D
I hope I can fix it... otherwise.... hmmm haha that could be difficult... I am really doubting there being any gk techs around here haha
-------------------------
by the way Craig could you give me a link to the mb200 thread were you discussed your problems in depth?
 
#20
Ok I went around with a chopstick... and well I didn't notice anything the sodder seems to be good.


I took it outside. So I could test it a little louder (there is a baby in the house)

So the I was wrong even in the aux in it is still messed up which means it has to be the main amplifier unit.
e
So the sound it trebly and quiet. When you play a bass not it farts out and is very distorted. You have to turn the volume up to about 6 clock before it starts to get loud, but it sounds awful. Unlike at my house before it traveled where a 6 was a nice growly loud sound.
The limiter which is supposed to keep the amp from distorting does not keep it from distorting it takes away some, but I think it works it just wasn't meant for whatever problem this amp is having.
So does anybody have any ideas what might be up? I find this issue so weird just that its a solid brand new amp. There is no cosmetic damage on it. I mean I know it got jossled a good amount when it flew, but still the amp parts are really light.

maybe later I can get a video of the sound and put it on youtube to better help you guys understand the issue.
thanks again
shalom,
Matthias
 

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