Mrak III cap question - Mandatory replacement or not?

[stokes]

Any way you can advise on a MK IV. I have the power board lifted. I only had to desolder one wire going to the switch. Getting to the underside of the 3 500V 30uf and bias caps looks challenging.Thanks[/quote]

I usually cut the leads on the old caps,so I have enough lead to put a heat sink on the lead left on the board so not to have to put heat on the pads on those PCB's,a little too much heat and you're adding jumper wires.I then twist the lead of the new cap to the lead left on the board,add a heat sink between the cap and solder point and solder.The Mesa PCB's are a bit better than some others,like the new Fender PCB's,those are very fragile.

 

[glip22]

Thanks for the help. It looks like it will be tough to get an iron topside between the 30uf caps and the chips on the board.

 

[stokes]

Thanks for the help. It looks like it will be tough to get an iron topside between the 30uf caps and the chips on the board.

I've done quite a few MKIV's with no problem.I dont know exactly what "chips you mean,but if you dont think you cant fit the iron between them and the cap itself,just twist the cap lead and the lead on the board near this chip and leave the cap standing on end so you can bring the iron in from the area where the cap will sit when you lay it down to connect the other lead.

 

[glip22]

Thanks for the help. It looks like it will be tough to get an iron topside between the 30uf caps and the chips on the board.

I've done quite a few MKIV's with no problem.I dont know exactly what "chips you mean,but if you dont think you cant fit the iron between them and the cap itself,just twist the cap lead and the lead on the board near this chip and leave the cap standing on end so you can bring the iron in from the area where the cap will sit when you lay it down to connect the other lead.

That would work. I got under the power board no problem. I would kie to do it from under the board but that does not look like it's worth it. Are you saying to still leave some of the old leg on and solder the new ones in that way, or can I do the job by heating from the top and completely removing the old lead9Probably not). Thanks for the idea on how to do the closest to chassi sid where it's tight.

 

[stokes]

No,I leave about 1/2 inch of the old lead,the idea is that you dont have to apply heat to the board at all,just snip the old cap out close to the body of the cap.You can then put an alligator clip between the board and the solder point and another between the cap itself and the twist that you now solder,no excessive heat gets to the board or the cap.Lifting the board and removing the old cap lead entirely is "neater",but if you are careful it can be done neat enough.I just find its safer to not have to disconnect leads,like the HT leads BB mentioned,or jostle any connections if you dont remove them,and the less heat you have to apply to those PCB's,the better,like I said,some of them are too fragile (cheap).

 

[glip22]

No,I leave about 1/2 inch of the old lead,the idea is that you dont have to apply heat to the board at all,just snip the old cap out close to the body of the cap.You can then put an alligator clip between the board and the solder point and another between the cap itself and the twist that you now solder,no excessive heat gets to the board or the cap.Lifting the board and removing the old cap lead entirely is "neater",but if you are careful it can be done neat enough.I just find its safer to not have to disconnect leads,like the HT leads BB mentioned,or jostle any connections if you dont remove them,and the less heat you have to apply to those PCB's,the better,like I said,some of them are too fragile (cheap).

Thanks Stokes. How do you replace the smaller caps at the other end of the board? Two are 63v 220uf and their are two 100 volt caps as well.

 

[stokes]

Unfortunately,the caps that are "on end" have to be unsoldered at the board.The bias caps sit on the side like the big electro's,and can be clipped.

 

[Monsta-Tone]

Mike B. told me the same thing. But so far, every customer I have has been very pleased with the differences that a full cap job has made in their amps!
The opinion that I got from him was about not filling the landfills up with toxins.

I've done a lot of partial cap jobs to experiment, then later on, replacing the 30 mf caps. There is always a noticeable difference after changing the preamp filter caps.

I use direct replacements from Mesa. I think that it keeps the amp looking stock (Yeah, I'm a mad scientist, but I like it to still look stock), and they are really good quality, American made caps.
On the downside of the direct replacement argument.....most of the smaller caps I get from Mesa are Illinois.

I wouldn't replace the caps on a Mesa unless it was made after a certain year though. I do make a habit of replacing them in my amps if they are over 10 years old though if I'm in there to do anything else. I simply don't want to have to do it later.


And.... :shock: $200 for a cap job??? :shock:
I get hassled over $150 and I clean all pots, jacks, and tube sockets while I'm there, as well as checking the bias and giving the amp a thorough run down. :lol: Guess I'm living in the wrong place! :lol:

 

[glip22]

Mike B. told me the same thing. But so far, every customer I have has been very pleased with the differences that a full cap job has made in their amps!The opinion that I got from him was about not filling the landfills up with toxins.

I've done a lot of partial cap jobs to experiment, then later on, replacing the 30 mf caps. There is always a noticeable difference after changing the preamp filter caps.
I use direct replacements from Mesa. I think that it keeps the amp looking stock (Yeah, I'm a mad scientist, but I like it to still look stock), and they are really good quality, American made caps.
On the downside of the direct replacement argument.....most of the smaller caps I get from Mesa are Illinois.
I wouldn't replace the caps on a Mesa unless it was made after a certain year though. I do make a habit of replacing them in my amps if they are over 10 years old though if I'm in there to do anything else. I simply don't want to have to do it later.
And.... :shock: $200 for a cap job??? :shock:
I get hassled over $150 and I clean all pots, jacks, and tube sockets while I'm there, as well as checking the bias and giving the amp a thorough run down. :lol: Guess I'm living in the wrong place! :lol:

Do you do yours the way Stokes recommends on the MK IV? By cutting the old leads and soldering to them.

 

[Monsta-Tone]

I cut the leads at the cap and use a pair of pliers to pull the cap out. Then I unsolder the lead and scrape the old silicone off of the board with my thumb nail or a razor blade if it's stubborn.
I then re-solder the new caps in after I check the length of the leads on the 30 mf ones.
I also apply a small amount of automotive clear RTV silicone to the underside of each cap and between them if they are going to touch.

I prefer this method because it looks like a factory job, other than the changed date and the "M-T" on the new ones.
If I were not used to doing it this way, I would definitely leave the original leads soldered to the board and bend them over to solder the new ones to.
Mesa boards are really much better than the newer Fenders or any Marshall PCB but they are still fragile. Especially if they have been hot in the past. I have had a few issues with Heartbreaker boards. The traces don't seem to be glued to the board very well on some of the earlier ones. Mark III's as well.


I do use an alligator clip (like Stokes suggested) as a heat sink. It seems to help a lot!

 

[glip22]

I cut the leads at the cap and use a pair of pliers to pull the cap out. Then I unsolder the lead and scrape the old silicone off of the board with my thumb nail or a razor blade if it's stubborn.
I then re-solder the new caps in after I check the length of the leads on the 30 mf ones.
I also apply a small amount of automotive clear RTV silicone to the underside of each cap and between them if they are going to touch.
I prefer this method because it looks like a factory job, other than the changed date and the "M-T" on the new ones.
If I were not used to doing it this way, I would definitely leave the original leads soldered to the board and bend them over to solder the new ones to.
Mesa boards are really much better than the newer Fenders or any Marshall PCB but they are still fragile. Especially if they have been hot in the past. I have had a few issues with Heartbreaker boards. The traces don't seem to be glued to the board very well on some of the earlier ones. Mark III's as well.
I do use an alligator clip (like Stokes suggested) as a heat sink. It seems to help a lot!

Thanks. I guess my question is can you replace them without removing the board? The power board was easy to lift but that main board . I do not want to try to desolder the old ones from the top without advice first.

 

[glip22]

I cut the leads at the cap and use a pair of pliers to pull the cap out. Then I unsolder the lead and scrape the old silicone off of the board with my thumb nail or a razor blade if it's stubborn.
I then re-solder the new caps in after I check the length of the leads on the 30 mf ones.
I also apply a small amount of automotive clear RTV silicone to the underside of each cap and between them if they are going to touch.
I prefer this method because it looks like a factory job, other than the changed date and the "M-T" on the new ones.
If I were not used to doing it this way, I would definitely leave the original leads soldered to the board and bend them over to solder the new ones to.
Mesa boards are really much better than the newer Fenders or any Marshall PCB but they are still fragile. Especially if they have been hot in the past. I have had a few issues with Heartbreaker boards. The traces don't seem to be glued to the board very well on some of the earlier ones. Mark III's as well.
I do use an alligator clip (like Stokes suggested) as a heat sink. It seems to help a lot!

Thanks,Can this be done without removing the main board. Will I be able to completely get the old ones out by only soldering from the top of the board? My MK IV is a 93.

 

[Monsta-Tone]

It's been a while since I worked on a Mark IV, and I don't have my office computer set up yet, so I can't say for sure.
Almost every Mesa amp can be done from the top of the circuit board, but I seem to remember the IV's have a double sided power supply board.

Boogiebabies or Stokes probably work on way more of them than I do, sorry.
If I get my office computer hooked up today, I'll look at the pictures and let you know.

Basically, if you have 2 220 mf filter caps under a small board on the power cord side of the amp, then you'll have to remove that board. I just flip them over and that seems to work fairly well. I hate removing boards, so I try to find ways to avoid it.

 

[glip22]

It's been a while since I worked on a Mark IV, and I don't have my office computer set up yet, so I can't say for sure.
Almost every Mesa amp can be done from the top of the circuit board, but I seem to remember the IV's have a double sided power supply board.
Boogiebabies or Stokes probably work on way more of them than I do, sorry.
If I get my office computer hooked up today, I'll look at the pictures and let you know.
Basically, if you have 2 220 mf filter caps under a small board on the power cord side of the amp, then you'll have to remove that board. I just flip them over and that seems to work fairly well. I hate removing boards, so I try to find ways to avoid it.

Thnaks Bro, I did remove the power board and replaced the two 220uf caps. I had to desolder and solder the top and bottom traces. I am holding off on the other 30uf caps until I figure out the best way. So far I am siding with Stokes, but if it can be done from topside I would rather do it that way for cleanliness. This amp is as mint. I am assuming the 30ufs on the main board are top and bottom soldered as well. If not then I can do it from the top only. There is no way I am risking removing that board on an 18 year old amp. Way too many joints to jostle around. Thanks for everyone's help.The other question I have is a little ghosting normal for the MK IV. I still have some after doing the two 220uf's.

 

[Monsta-Tone]

Yeah, I think Stokes way is the safest for you.
But...be really careful removing the old capacitors. Sometimes the glue that Mesa used is really strong still. Make sure you are careful and take your time getting them out or you will have some serious repair issues on your hands.

 

[glip22]

Thanks for the help. I replaced the preamp caps and the other four smaller caps from the topside of the board and completely removed the old leads. Job came out perfect. I was shitting myself when I fired it up worried that one of the leads was touching the chasis. I was very carefull about it and I was in luck. All voltages and tube bias looks good. Now I am wondering if there is anything else I could do to make the amp better. I was thinking on replacing the four large wire wound resistors on the power tube sockets to ground. The schematic shows them to be be 2.2K, and 2.2 meg. Any other advise on resistor changes will be appreciated.

 

[stokes]

Why would you want to change out those resistors?If it aint broke........ Parts like the filter caps and tubes wear out over time and use,unless those resistors are bad,just leave them.

 

[glip22]

Why would you want to change out those resistors?If it aint broke........ Parts like the filter caps and tubes wear out over time and use,unless those resistors are bad,just leave them.

I thought these types of resistors will drift quite a bit over years. The amp is 18 years old. If you think they should be in spec, I agree I should leave them alone. I cannot get a reading on them while in the circuit.

 

[Monsta-Tone]

Sorry,
I didn't mean to start anything. I was talking about the carbon composition Plate Resistors on the preamp tubes drifting and causing a lot of hissing in some of the older Mesas.

So far, I haven't had very many carbon comp resistors in the power supply or power amp sections go bad or drift very far out of spec.


I would leave these ones alone.
At this point, if you want it to sound better, start experimenting with different tubes.

 

[glip22]

Sorry,
I didn't mean to start anything. I was talking about the carbon composition Plate Resistors on the preamp tubes drifting and causing a lot of hissing in some of the older Mesas.

So far, I haven't had very many carbon comp resistors in the power supply or power amp sections go bad or drift very far out of spec.


I would leave these ones alone.
At this point, if you want it to sound better, start experimenting with different tubes.

You didn't start a thing. You have been nothing but helpfull.