Swap rail caps with the power caps or just power caps?

[Lance_S]

Hey guys.

I have 2 MS2125's and an MS275 that I am about to do a cap exchange on. Some say don't worry about the rail caps, they don't go bad. Others say, while your in there.... This is my first swap so I don't want to make it more complex that it already is. Just wanted to get you opinions on whether to do all of them or just the smaller ones.

Thanks,

L

[The Golden One]

the rail cap's are case sensitive manly because the only reason they go bad is if the amp was overly abused for a long time, you know if someone ohmed it down and cranked on it. the rail caps are fairly durable and extreme heat is the main reason they can go bad, you can slide a thin piece of paper under the rail cap's to see if they have leaked, and sometime's you can almost just tell by looking at the outer heat shrink to see if it's gotten smaller, if so it could be an indication that they have seen allot of heat.

[ttocs]

caps that have not been used are just as suseptable to leaking and problems as caps that have been driven, sometimes more suseptable really. If you are going to be in there doing it then go ahead and do it all. I was amazed in tech school the kind of "POP" a small cap can make and you wouldn't want that in your amp. Those caps could very well be good for another 5-10 yrs but who knows and no one wants to take their system apart to redo the caps(the octane in my truck knows this). While you are in there go ahead and do them IMO, I am doing it on my mq-430. Basically to make it easy, why not err on the side of safety since they will only be a couple of bucks more and a little more time? That time/money is much much less then if you do have a cap pop and need to consider repairs.

[stipud]

Since MS amps take forever to disassemble and reassemble, I usually advocate doing the rail caps in them "while you are in there", though they rarely fail like the power supply caps do. However the one thing you have to take care of, is that the rail caps are snap-in type, which makes it really easy to rip out the vias (small ring conductors that connect the top and the bottom of the circuit board, through the hole that the cap installs through).

Check out my MS capacitor replacement thread in the FAQs... there is a method for ripping out the power supply caps that makes it way less likely to pull a via. Unfortunately that can't be used on the rail caps, so you have to back them out manually. Take care and if a via is torn out you will have to lay some sort of connection down in its place. Some people use the copper solder sucker braid as a replacement.

[ttocs]

I have always wondered why we recomend removing them like we do? I have always had better luck with the solder remover, the iron with the bulb on it to suck it out? Doesn't take as much heat as the solder wick and also does a better job.

[pimpinest123]

Is there a certain brand of caps to use so they aren't to dissimilar to the ones that r in the ms amps

[Lance_S]

Well, this is interesting. I have an MS275 that is in great condition and has been taken care of but it has the original caps in it. The twin MS2125's are brand new in box. I purchased the ones that were advertised here on the board. They are in transit as we speak so they literally have 0 hrs on them. I want to bench test them to make sure they run but everywhere I have read says DON'T PUT POWER TO THEM UNTIL YOU REPLACE THE CAPS!!! So I am not sure which way to go on that. Either way, they are still 15 year old amps so I was planning on changing the caps out on all of them at the same time. Like Ttocs mentioned, caps that haven't been used are still susceptable to leaking.

My thought on the big caps was like yours, might as well since I am in there. I obviously don't want to go back a second time, at least not for 20 years!

I have been through the MS cap exchange and read it over about 5 times. I will certainly use it as a reference step for step. The caps I am planning on ordering are the Nichonson's I believe they are 5000 hrs at 105c. Which should be fine. There is the panansonic option but I doubt you could hear a difference. The main caps I i go with the other ones mentioned in the how-to thread, I don't remember the name of hand. I have to double check the volts on the mains on the 2125. I think someone mentioned they thought they were 50v vs. the 35v on the ms275. Again, I just have to double check when I get in there.

I will take some pics when they get here. Should be neat to see a pair of ms2125's new in box. I expect them on monday.

Thanks,

Lance

[stipud]

Lance, you can check for leakage by sliding a sheet of paper underneath the caps and seeing if there's any goo, but if you are planning to replace them anyways you might as well do it first. Just take care of those vias, because you can hurt the amplifier just as much as a shorted capacitor can by having one of those go missing!

[Lance_S]

Thanks, will do.

[Eric D]

This is somewhat a rehash of what others have posted, but most anyone can change the input caps to the amp. If you get one wrong (so long as you don't get it backwards), either damaging a via or cold solder etc, the amp will still work. In the case of an amp with say 4 input caps, it will work with just one in there, and in some cases it will work with with none of them in there.

The rail caps are another story. If you make a mistake and don't have a good connection with the rail cap (say from a damaged via), which you power the amp up, a whole bunch of components will end up seeing higher voltage than they are rated for, and will fry instantly. You then have to track down what fried and that is not fun. About 50% of the amplifier repairs I have done for people in the past few years has been to fix the damage caused from attempting to change the rails caps and not getting it right.

So, for this reason I discourage changing the rail caps. However, if your soldering skills are pretty good, and if you have a DMM so you can verify a good connection on the caps prior to turning the amp on, then you don't have much to worry about.

[Lance_S]

Eric,

Thank you for the post. That is the type of info I was looking for. I have, in the past, went into projects and broke more than I fixed. Of course, that's how we learn but I would prefer not to learn on these amps. They are tough to replace. I will slide some paper under them, give them a really good going over and make a decision. Maybe the best thing to do is post some close up pics when they get here and have you guys give me your opinion. Honestly, the 2 2125's haven't seen any time so the caps should be in great shape. I know they can leak over time but I also know that abuse can speed up the process. These amps certainly haven't seen any of that so I should be good. I will take some pics and post.

Thanks again.

Lance