Pulling a Mark III PCB

[RyanScott80]

I bought a red stripe last year that was in rough condition, but nothing that couldn't be fixed. Filter caps were leaking, a pot shaft had broken clean off, the grille cloth needed replaced, the fan was missing, EQ sliders were seized up, and the tolex was beyond filthy. I knew all of this when I bought it, and paid well below the market price.

I've addressed all these issues, and the last thing I need to do before I call this restoration finished is to replace all the original electrolytic caps on the main board. I know most of them are accessible from the top, but some are in a densely populated area of the board, making it difficult to work from the top. I also can't replace the radial cap without getting underneath it. I'd prefer not to clip and solder to existing leads, even though that might be considered acceptable. Before I dig into this, what is the best approach to get the board out with minimal desoldering? I don't do this professionally, but I have a background in engineering and I'm not new to working on amps. I've done builds, mods, and maintenance on a few different amps, and I know how to work safely. I'm just not used to dealing with the rats nest of a Mesa chassis, I come from the Marshall world. If anyone has done this and can offer advice on the cleanest way to get it out, it would be much appreciated. Thanks.

 

[woodbutcher65]

A certain amount of desoldering is required. Just carefully document every wire and where it goes, with photos, tags on the wires, notes, whatever you need to do in order to have no doubt about where every wire goes. And then just do it.

Sometimes you just have to rip off the band-aid. Desolder those wires, pull the board, do the work, reinstall. It's a lot easier to do it this way than to try to remove the absolute minimum of wires and have the board half out and at a funny angle, under stress, making you hate life for a while.

 

[electric mayhem]

I bought a red stripe last year that was in rough condition, but nothing that couldn't be fixed. Filter caps were leaking, a pot shaft had broken clean off, the grille cloth needed replaced, the fan was missing, EQ sliders were seized up, and the tolex was beyond filthy. I knew all of this when I bought it, and paid well below the market price.

I've addressed all these issues, and the last thing I need to do before I call this restoration finished is to replace all the original electrolytic caps on the main board. I know most of them are accessible from the top, but some are in a densely populated area of the board, making it difficult to work from the top. I also can't replace the radial cap without getting underneath it. I'd prefer not to clip and solder to existing leads, even though that might be considered acceptable. Before I dig into this, what is the best approach to get the board out with minimal desoldering? I don't do this professionally, but I have a background in engineering and I'm not new to working on amps. I've done builds, mods, and maintenance on a few different amps, and I know how to work safely. I'm just not used to dealing with the rats nest of a Mesa chassis, I come from the Marshall world. If anyone has done this and can offer advice on the cleanest way to get it out, it would be much appreciated. Thanks.

Snip and solder is the safe way for the PCB.
Without a fancy de-solder station all you need is a solder sucking pen or wick. You do not need to pull the board. I like my cheap pen.

A pair of cheap snippers with an undercut angle are key. You can get under the leg of a radial, snip, pull the cap over to get at the 2nd leg and pull the cap. Then with needle nose on the snipped leg, heat and pull. At this point suck the solder.

Looks way better and this is what I do most of the time but it endangers the tracing. A clunky slow heating iron would be a bad tool to be using.

 

[RyanScott80]

Snip and solder is the safe way for the PCB.
Without a fancy de-solder station all you need is a solder sucking pen or wick. You do not need to pull the board. I like my cheap pen.

A pair of cheap snippers with an undercut angle are key. You can get under the leg of a radial, snip, pull the cap over to get at the 2nd leg and pull the cap. Then with needle nose on the snipped leg, heat and pull. At this point suck the solder.

Looks way better and this is what I do most of the time but it endangers the tracing. A clunky slow heating iron would be a bad tool to be using.

I have a Hakko vacuum desoldering tool and a good adjustable soldering station. I've already replaced the filter caps on the power supply board, which is probably much more fragile than the main PCB. Those traces looked like they would fall off if you looked at them the wrong way.

What I'm really trying to avoid is desoldering wires from the board in the process of removing it. I don't want to heat the pads multiple times if it can be avoided. Much easier and safer to desolder from a pot, tube socket, or ground connection.

 

[Theresa]

It's a lot easier to do it this way than to try to remove the absolute minimum of wires and have the board half out and at a funny angle, under stress, making you hate life for a while.

We've all been guilty of that, now haven't we? LOL

 

[RyanScott80]

We've all been guilty of that, now haven't we? LOL

I did get that suggestion from a tech who works on Mesas. Remove all the pots and the EQ sliders and tilt the board at enough of an angle to get underneath it without any desoldering. Not sure how well that would work, since some of the caps sit in the bottom left corner toward the back of the amp.

 

[woodbutcher65]

If you think snip and solder is the only safe way to handle a PC board, then I must assume you've never been formally trained in soldering techniques. There are times where snip and solder is required but Mesa's PC boards are high quality with heavy traces and they don't try to shove too big a wire or component lead into too small a hole, which makes it almost impossible to desolder the connection completely via wick or vacuum. Use a good iron, and good clean wick, and maybe a drop of added solder to freshen up the connection and it'll desolder just fine. Just don't apply force. You don't have to if the desoldering job is done right.

And don't snip any leads. You may NEED all the wire length. Shortening some wires AT ALL may make it impossible to reconnect them, necessitating a splice or replacement of the wire. That's a step backwards.

 

[electric mayhem]

I have a Hakko vacuum desoldering tool and a good adjustable soldering station. I've already replaced the filter caps on the power supply board, which is probably much more fragile than the main PCB. Those traces looked like they would fall off if you looked at them the wrong way.

What I'm really trying to avoid is desoldering wires from the board in the process of removing it. I don't want to heat the pads multiple times if it can be avoided. Much easier and safer to desolder from a pot, tube socket, or ground connection.

All my gear is Hakko- sounds like you have that covered.

With the vacuum I don't get why you want to pull the board. It'll do just as clean a job on top. My snip and solder was just a best practice for old amps. As I said it's not my typical MO. I don't like the hacked look even if it is a safe approach.

But I'll snip one leg of radial caps all day before I pull all the pots or desolder wires.

I don't know how that got to snipping wires since leads are on caps and resistors and if you are replacing them snipping them isn't moving backwards or doing anything anyone needs to yell about. And formal training for soldering? Wow. Is there a club too? No wait- I'll stay in the dregs of societal soldering.

 

[RyanScott80]

The radial cap is fully seated against the board, there's no way to get to it without having access to the underside. Unless someone is brave enough to cut it in half near the bottom to get to the leads, which I'm not. Not sure about the Mark III, but those radial caps are a frequent source of issues on the Mark IV.

Working from the top is fine if you have easy access to all the components, but that isn't necessarily the case here. Mesa likes to put a bunch of components right next to each other, making it a challenge to get an iron in without burning something. After all the work I've put into restoring this one, I just want to make sure this last step is done properly.

 

[woodbutcher65]

Formal soldering training can be as simple as being taught by someone who's experienced with industry standard practices in the electronics mnaufacturing and repair industries. You can even learn from books, or even online guides. There are youtube videos that can teach you. It doesn't have to be a semester credit hour at the local community college.

 

[domct203]

Formal soldering training can be as simple as being taught by someone who's experienced with industry standard practices in the electronics mnaufacturing and repair industries. You can even learn from books, or even online guides. There are youtube videos that can teach you. It doesn't have to be a semester credit hour at the local community college.

+1

Practice with some wire and perfboard. Once you are getting good clean joints build a couple of pedal kits.

Dom

 

[electric mayhem]

+1

Practice with some wire and perfboard. Once you are getting good clean joints build a couple of pedal kits.

Dom

This.
Experience and repetition. I cut my teeth on 3 x CAPI- pre-amp, 11 space rack and PS that wasn't recommended for beginners but was fun and not overly complicated. Unless you are lazy and using a wave you can't put together an 11 rack without getting the experience to move forward or know it's not for you.

If you have a good station soldering is the easiest thing in the world.
What you need to know about soldering an eyelet is the same thing as welding. Get in there with the appropriate heat, don't over do the bonding metal and get out as quick as you can so as not to damage or weaken what you are working on. Anybody want to try soldering- there's your formal training.

Then go get the game operation and play it until you don't get buzzed. Not touching wires (insulation), keeping a steady hand and knowing when to remove things to make the job easier and cleaner are the real challenges. I could teach a 7 year old in 5 minutes to get in and out of a good solder joint and in 10 minutes have them soldering running leads like an old Mark PS board. You do not have to be a special person to do such a menial task as soldering people! Dew it! Everyone needs cables- grab some nuetrik connectors and mogami wire and have at it.

I can braze, do farm welds, run designs in EE simulators, dig a basement with a loader to a 1/10th of a foot standard, do a radio show on technical stock analysis and in the last year have the confidence to not only fix a tube amp but have a good understanding of what makes an early Mark tick at each triode.
Not because I'm special. Not because I hold my chest out regularly telling everyone I'm a professional at my trade and then give out dangerous and cavalier mis-information about boogies on a boogie forum.
Because I dew it and I always dew it and I ask a lot of questions of the right people. Ahhh, the right people! And there are so many people on this board that while not as cavalier have tremendous knowledge and experience.
I am extremely thankful for all the great people that make a great place great.
Thanks to all the fine people here!