Mark III series 300 capacitor HELP!!!

[FembotsBeach]

Hey guys,

I just got a Mesa Boogie Mark III Coliseum 300 Blue Stripe head.

There was a loose capacitor inside the amp.
The picture of the capacitor:

http://i5.photobucket.com/albums/y151/shredentz/capacitor.jpg

Info:

AM, 3300uF, 16V, ROK 8852, AGR 85°C

The board seemed to be fine though, but I'm no expert on these things:

Pictures of the board:

http://i5.photobucket.com/albums/y151/shredentz/boogie/boogie10.jpg
http://i5.photobucket.com/albums/y151/shredentz/boogie/boogie11.jpg
http://i5.photobucket.com/albums/y151/shredentz/boogie/boogie12.jpg

I'm not sure if the capacitor came off the board or it was just lost in the amp :lol:

I appriciate any info.

Thanks!

 

[bentium]

i believe this one must be installed on the top left side of the board


considering this is only a 16V, it is probably going to be of some a filtercap, for the dcpowersupply of the optocouplers or something, so nothing realy big

i dont have the schematic of the specific type of amp (mark3 coliseum) but i suggest that you take the amp to repair, it wouldnt cost you much (new cap, 0,5h work)

 

[Boogiebabies]

Does the amp work?

The only place that cap is used is in the LDR power supply and your board has it. It does look like it has been replaced. If your channel switching works, the I would suspect the person who replaced the cap left it rolling around in the amp. I have seen this many times before.

Regardind the missing 30uf/500V cap from the preamp board, you may want to call Mesa and see if there was a reason it was omitted from the K series amps, or if you actually need that third filter cap.

 

[FembotsBeach]

I haven't played with the amp yet as I don't have a cabinet in my apartment right now. Also, I need a 220V-to-110V step-down converter because I live in Europe (there isn't a Mesa distributor in my country). I can test it durning the weekend.

The blue 16V capacitor is the only one with two "contacts" on one side.
http://i5.photobucket.com/albums/y151/shredentz/capacitor2.jpg

So I looked the board more carefully and discovered this spot, Bentium you were right

http://i5.photobucket.com/albums/y151/shredentz/boogie10marked.jpg

a closer look

http://i5.photobucket.com/albums/y151/shredentz/board.jpg

I'm pretty sure this is the right place, the capacitor perfectly suits with the board there

http://i5.photobucket.com/albums/y151/shredentz/boardmarked.jpg

A similar if not the same capacitor is on the same place on "usual" Mark III boards

http://i5.photobucket.com/albums/y151/shredentz/IIIgutsmarked.jpg

Anyway I'm still not sure if the cap came off durning the shipping or it is left there. The previous owner was a little worried when I told him about this problem.

So if it really came of, it disables the channel switching? Does it disables or ruins anything else?

Boogiebabies, there is a third 500V cap place but it looks like it has never been on the board, I have to talk withe the Mesa folks about this one.

 

[Boogiebabies]

The only problem is if the cap was broken off, it would have left the legs and maybe guts behind. Those pads look like they were desoldered.
Judging by it's position, and what schematics we have available it looks like the 3300uf/16V coming of the integrated bridge rectifier for the heater supply, relay and R2 LDR.

 

[FembotsBeach]

I'm not really sure if the cap was broken off or desoldered. The cap's legs are uneven, one is about 1mm and the other one is about 0.5mm. The pads look ok, but if I watch real closely then there's a tiny spot on one of the pads wich could be a cap's leg, if I touch it, I can gentely feel that there's some tiny "clod" about 0.01mm long if not less. I think it's a part of the cap's leg but I'm not 100% sure as it's so small.

 

[Boogiebabies]

It could be a sharp spot of solder. If the cap was removed by force, it would have probably pulled the pads and possibly some of the circuit trace.
With two sided boards, they are usually soldered with a flow gun from the bottom and then the leads are clipped. Whatever angle the cap was when the solder cooled is basically how the leads would look when trimmed.

 

[timv]

My mark 3 coliseum, blue stripe, is missing the 30 uf 500v cap to, it was never there. I think it is because the main b+ supply is beefed up for the coliseums. That cap definately looks like it came out of the spot you have circled because my amp has one just like it there also. Good luck.

 

[Boogiebabies]

Good call Timv. It's pretty hard to find multiple MK III K owners.

 

[FembotsBeach]

I'm getting it fixed tomorrow.

I also have 2 more questions.

1) Where can I find the K**** serial number?

2) I don't remember where the cooling fan's wires go :lol:

Looking at this pic:
http://i5.photobucket.com/albums/y151/shredentz/boogie/boogie07.jpg

the holes are near the right 12AX7 pre-amp tube.
So does the cooling fan's input wire (the thinner one, output wire is thicker) goes to the upper or lower hole?

 

[Boogiebabies]

The serial number should be stamped on th back. The fan plugs into the outlet at the edge of the chassis by the power transformer. You can see the plug from the gut shots, but it is cut off in your last picture.

 

[FembotsBeach]

Yeah the serial number is on the back, it's 25283 but I'm looking for the special Series 300 serial number, it should start with "K", they go from K423 to K500, I can't see it anywhere.

About the fan, I know where the plugs are but I don't remember in wich hole they go :lol:

These are the wires
http://i5.photobucket.com/albums/y151/shredentz/fanwires.jpg

and these are the holes
http://i5.photobucket.com/albums/y151/shredentz/boogie07marked.jpg

I'm not sure wich wire goes to wich hole.
Does the WIRE 1 (Red, Input) goes to the hole A (yellow) or hole B (Pink) ?

 

[Boogiebabies]

Those are the reverb cables. The white wire goes towards the back of the chassis and the grey goes towards the front. The fan is a 2 prong outlet by the power transformer (The Big One). Look next to it and it will be a brown old style outlet.

 

[FembotsBeach]

duh yeah those are reverb wires, being away from amps for almost a year makes me ask silly questions :lol:

anyway thanks man, I connected the fan wire

 

[Boogiebabies]

Sweet !!!

Take a look at the MK III/MK IV Noise debate regarding my comment on fan noise, just in case.

Enjoy.