Filter Cap Replacement - Leaving Old Filter Cap Wires Soldered

[Greenback25]

I talked to a new tech (old one is in retirement now) about the filter cap replacement job that my Mesa Mark III amplifier needs. He told me that these amps have very intricate PCB connections and paths and he doesn't want to mess with them due to potential cold solder joint possibilities.

Instead of completely removing the old filter capacitors and sodlering in the new ones, he said he's going to just clip the wires of the old filter caps and solder the new filter caps to these wires - that way he doesn't need to solder around the PCB directly.

Is this all around a bad idea or an acceptable solution to avoid potential PCB damage and cold solder joints?

[maxkracht]

Is this all around a bad idea or an acceptable solution to avoid potential PCB damage and cold solder joints?

I think it’s kinda sloppy, but if done properly will save time and money. It does create potential for making the old solder joint cold if he doesn’t heatsync the leads. I don’t think mesa boards are bad enough to require this. It’s possible he just doesn’t have much experience doing rework on old pcbs. You will tear off traces if you treat them like eyelets.

[xtian]

Which amp? The damnable Mark IVs and Vs make it very time consuming to lift the PCB. I'd solder new filter caps to existing leads if it was my own amp.

[nuke]

Back in the early days of circuit boards, the recommended way to accomplish repairs was to snip leads, and j-hook the new part leads into place and then solder. Even Fender recommended that approach in their very old service literature for eyelet boards. In the pre-circuit board days, Zenith, RCA, Sylvania and everyone else recommended that method for point-to-point constructed color TV chassis. I'm just old enough to have repaired some old, all-tube TV's when I was a high-school kid working in a TV shop.

So, I don't get upset when I see it done that way, if it is done well. The joint should be mechanically sound, then soldered neatly.

Today, the tools to safely unsolder and remove components from circuit panels is widespread and well-known. So mostly we de-solder with wick or vacuum tool, remove, clean up, solder the new part in at the board level, unless there's a reason not to.

Lots of Mesa are a pita to service. Not all modern circuit boards are robust either. Some of them have really thin foils, like the really low-end of Fender's tube amp lineup today, and are prone to damage with even careful work.

It is good your tech told you his plan. Seems like the right thing to disclose.

[jabguit]

Which amp? The damnable Mark IVs and Vs make it very time consuming to lift the PCB. I'd solder new filter caps to existing leads if it was my own amp.

"I talked to a new tech (old one is in retirement now) about the filter cap replacement job that my Mesa Mark III amplifier needs."
this should be a clue...

[martin manning]

Back in the early days of circuit boards, the recommended way to accomplish repairs was to snip leads, and j-hook the new part leads into place and then solder...

Fine if you have exposed leads that are long enough to work with. I don't know how you could replace radial caps this way.

Today, the tools to safely unsolder and remove components from circuit panels is widespread and well-known. So mostly we de-solder with wick or vacuum tool, remove, clean up, solder the new part in at the board level, unless there's a reason not to.

True enough, love my Hakko FR-301. Even so, this almost always requires lifting the board, often the most time consuming part of the repair

It is good your tech told you his plan. Seems like the right thing to disclose.

Might even be a good idea to quote a price for each way and let the customer decide.

[R.G.]

This is one of those places where nothing will substitute for experience. I've been soldering since the late 1960s; I would have no hesitation whatsoever in doing this. In fact, I have done it, many times. I would not trust a person with less than a decade of soldering experience to do this on a highly valuable amp without heatsinks on the leads.

Someone skilled and experienced can snip the old leads, bend a hook in the old leads and new part's leads, crimp them in place and solder them without a hitch. Someone with a just-barely-hot-enough soldering iron, maybe not using 60-40 or 63-37 solder and good flux will have to keep the iron on the joint so long that the heat will have time to travel down the old lead and melt the solder on the PCB.

The trick is to use a HOT iron, clean leads, and NOT lead-free solder; prep the joint, for extra points dab a little liquid flux on, get in fast with high heat, touch the solder to the side of the joint opposite to the iron, and remove the iron and solder when the liquid just flows to the iron tip. Then get out. Should be less than three seconds with the iron on the joint.

[FourT6and2]

It's fine. And depending on the length of the original lead that's left in place, sometimes it's better to straighten it so it stands straight up off the board like a fence post. Form eyelets in the new component leads that then slip down over the fence posts and solder that. Better than "J hooks" IMO. It will also depend on the weight of the new components and some other factors. But if the tech knows what he's doing, it's fine.

[nuke]

R.G. said it very well.

I worked my way through school as a tech, starting in high school in the early 80's, and I've been soldering since I was about 6, so I'm a little bit younger than RG probably. However, he may have been a toddler-prodigy.

I kid you not though, I had access to all of the major brand amp service literature in the music shop I worked at, going well back into the 1960's, and I worked in a very busy TV repair shop as well. They had a lot wealthy customers who kept their old RCA and Zenith all-tube color TV's going, because they were built as good quality furniture with real wood cabinetry and matched their home decor.

I kinda giggle at people saying p-to-p amps like the Silvertone 1484 are a mess. They're not a mess, actually they're pretty nicely made for P-to-P. Some of those old color TV chassis were an absolute forest by comparison.

Even into the 80's with TV's still being made in the USA, much of the service literature recommended attaching repair parts to the old leads to avoid damaging circuit boards, and had a lot of cautious advice about replacing DIP package IC's. But by then, the boards were more robust than late-60's and early 70's circuit boards.

To get back to the OP's question, here's a picture of a Mesa MK-III that has been recapped by attaching to existing leads, at least the big ones. They stuffed one radial cap right into the middle of things. This is why I generally turn down working on these. The boards also kinda-suck and are easy to damage, in addition to being a total PITA and time-destroyer if you need get to something from the bottom side. (I just vadered the photo from the internet)

mesa-mk-iii.jpg

[Greenback25]

Thanks for all the helpful answers! I'll definitely trust the new tech then. Hopefully the recap wi'll turn out alright.