mesa dual rec cap job?

mrkrausman · Post by **mrkrausman** » Fri May 13, 2011 9:35 pm

Has anyone done a cap job on one of these? It's a 1993 Mesa Boogie Dual Rec and belongs to my brother who is considering replacing the electrolytics. He would like me to do it because a tech will charge many tokens. I have done a few of these replacements with vintage amps only where the caps are accessable. This looks tedious because all caps are on circuit boards. But I am always up for a challenge so I just may do it. However I am not familiar with working on circuit board amps so I am leary. Boost my confidence or tell me to leave it alone.

SteadyEddie · Post by **SteadyEddie** » Fri May 13, 2011 11:56 pm

I'm a marine electronics tech and it reminds me of changing the batteries in an AIS unit. This is how I'd do it without removing the circuit board:

Take a small pair of dikes and clip the cap out of the board, leaving the old leads still sticking out of the PCB.

You want to solder-splice the leads of the new cap to the old cap's leads. So take a pair of hemostats and use it as a heat sink where the old lead meets the PCB. This will keep that part of the old lead from heating up and loosening.

Tin the old and new leads. This is important. Put the new cap in place. Put the leads together on one side of the cap at a time, then take your soldering iron and with a clean tip, melt some solder so you have a little drop of solder hanging off the tip. Now, without waiting long, drag the soldering iron tip across both leads. Once the solder "wets" hold it in place until it cools.

mrkrausman · Post by **mrkrausman** » Sat May 14, 2011 12:07 am

SteadyEddie wrote:I'm a marine electronics tech and it reminds me of changing the batteries in an AIS unit. This is how I'd do it without removing the circuit board:

Take a small pair of dikes and clip the cap out of the board, leaving the old leads still sticking out of the PCB.

You want to solder-splice the leads of the new cap to the old cap's leads. So take a pair of hemostats and use it as a heat sink where the old lead meets the PCB. This will keep that part of the old lead from heating up and loosening.

Tin the old and new leads. This is important. Put the new cap in place. Put the leads together on one side of the cap at a time, then take your soldering iron and with a clean tip, melt some solder so you have a little drop of solder hanging off the tip. Now, without waiting long, drag the soldering iron tip across both leads. Once the solder "wets" hold it in place until it cools.

Thanks, exactly what I was looking for. I have been studying schematic and have all of the values figured out for ordering. I think I can get all of them by your method except for the 2 smaller upright (radial) cans. I believe they are cathode caps (1uf) for V1 and v2. If so they are kinda critical

SteadyEddie · Post by **SteadyEddie** » Sat May 14, 2011 4:04 pm

Yeah, if you want to get to those two caps you're gonna have to get to the underside of the board. It's hard to tell from the photo how much of a PITA that's going to be.

mrkrausman · Post by **mrkrausman** » Sat May 14, 2011 5:53 pm

SteadyEddie wrote:Yeah, if you want to get to those two caps you're gonna have to get to the underside of the board. It's hard to tell from the photo how much of a PITA that's going to be.

Ya all I have is the photo right now. Those 2 I am not sure where they go or their values until I get it on the bench and also the preamp sockets are under the board. Why would they design a an amp this way? It is a PITA. If I where him I would unload it now but he loves it cuz it's switching machine.

SteadyEddie · Post by **SteadyEddie** » Sat May 14, 2011 7:47 pm

If those two caps are 1uf I would replace them with a film type and never worry about them again.

mrkrausman · Post by **mrkrausman** » Mon May 16, 2011 11:23 pm

SteadyEddie wrote:If those two caps are 1uf I would replace them with a film type and never worry about them again.

Well my brother spoke to a Mesa Boogie tech and he recommended NOT to change caps until they appear to be leaking. He says they see 30 year old amps all the time that have healthy caps. The tech seemed irritated that he was getting this question pretty often and considers it a ploy by amp guys to get bench money :-/. In reality, some of us don't make a dime for this work. I don't know if I buy the 'waiting for a leak' method but this job has been cancelled for now.. Anyway thanks for your help Steady. I put your suggestions in my amp files. I'm sure it will come in handy on other amps. I have a 1980 JMP 2203 on the way with original caps so I will make the call and switch those for sure and it will not be a PITA

Cheers, Mike

robert · Post by **robert** » Tue May 17, 2011 6:21 am

Hi Mike,

interesting!

But: have you asked this Boogie-guy why they insist on the use of their "Original Mesa Boogie selected" tubes, intead of simply installing a Bias- pot in their amps?

Well, I think: it's all about the same thing: "making money out of it"

I personally wouldn't trust 30 year old elecrolytics in an amp!

On the other hand: a tech (with enough patience, it's only a matter of time...) can charge much more money for the replacement of exploded caps in an amp and the "included" cleaning & repair ...

Regards

Robert

jamme61 · Post by **jamme61** » Mon Jun 13, 2011 5:05 pm

I did a cap job on my mesa tremoverb same filter layout. You don't have to remove the board, you can solder from the top of the board(mesa uses double sided boards) l also I used F&T caps which are smaller in size and made the job even easier. I changed them because they were twenty years old, they were still working.

soundguruman · Post by **soundguruman** » Sat Jul 09, 2011 8:55 am

First
You do not usually need to change the caps in an amplifier, unless they are really old. Leaking electrolyte is one sign that they need to be changed. Also they may increase in 60 cycle hum, the cap is becoming open circuited, or has been overheated for a long period. Also, caps can short or start to draw excessive current (they may not be leaking fluid) and need changing. BUT you should be testing this, not assuming.

And one reason I would want to change the caps is to modify the power supply for less ripple, and use much better filtering, or chokes....which means a different value, voltage rating, of capacitor. I would probably mount can caps instead of using the axial lead caps.

Second, if you do not have the training and experience to work on this amp, you have no business messing with it. This is an amp for an experienced person, who has safety training. It's dangerous, and presents a lethal shock hazard.
The capacitors store a charge after the amp is disconnected from power, and that charge can stop your heart from beating.

Third, to all you guys who won't take the circuit board out...
and clip the leads, and try to solder caps in from the top of the board...and all the other "pretend" repairs you do...
This is really Mickey Mouse, a total amateur slop job. Either build the amp the right way, like the factory builds it, or don't build it at all.

If the amp does not comply to factory standards of workmanship, start over.

Why is it that there is always time to do something over, but never time to do it right?

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