ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Investing a few extra seconds in good soldering technique can add years of lifetime to your newly-restored appliance, regardless of whether you use run-of-the-mill, or high-quality capacitors.
The manufacturer has (or has not) invested quality control during the manufacture of the component, but how the technician chooses to install and solder it in the PCB, will determine the actual lifetime, irrespective of what is claimed on the datasheet.
Here is a perfect example.
I was repairing a VCR (which had a sticker at the rear, showing the date of last repair as 3-2013), and in the power supply, there were 3 replaced 22uF 63V 105-degree capacitors, made by Samwha (Samsung Industrial) series RD. These are the EXACT capacitors which we find in many recent B&O products.
The 3 capacitors had all failed, with capacitance of between 6-10uF, and ESR more than 20 ohms. The cause of failure was quite obvious.
The lazy repair tech simply pulled the leads apart to fit in the 5mm PCB holes. Doing exactly that, irrevocably compromises the rubber seal position, and the electrolyte leaks out.
In the picture, you can see the gunk on the legs.
This piss-poor laziness, unfortunately, is standard procedure among most technicians.
If you want your capacitors to last, it is essential to bend the leads twice at 90 degrees (almost), as shown in the Panasonic EB at the left, so that the leads pass through the rubber seal without compromising its leak-proof ability.
Menahem
Interesting theorie Menahem.
You think that the capacitor has leaked because of the bad bend solder lead instead of the work-stress where it is under? Does this powersupply has a traditional powerhandling or does it have any form of PWM ?
With the latter, almost every capacitor in even nowadays designed switching powersupply's doesn't seem to have a lifetime lifespan
This is a PWM, but the actual circuit voltage is only 12.7V.
You can see that this cap is rated @ 63V.
So, this cap should have been just relaxing.
I can only guess that the original cap was a 22uF 16 or 25V, but the tech obviously keeps a limited stock on hand, applying the stupid (for techs anyway) maxim "One size fits all".
A year ago, 7 caps were replaced in the PSU, all of them rated @ 63V. None of the circuit voltages on the secondary side approach anywhere near that.
Menahem Yachad: This is a PWM, but the actual circuit voltage is only 12.7V. You can see that this cap is rated @ 63V. So, this cap should have been just relaxing.
Forgive my ignorance but isn't ripple current what's killing the cap? The high frequency content of the PWM signal?
I'm asking because I'm curious.
/ Johan
You are entitled to believe and think, what you like but claiming the leaks has somethingto do with the components pins being bent, I think, must be on your own account, Menahem.
It's quite common to see caps leaking like this, also factorymounted ones that never had their pins bent in any way.The Beocenter 2100/2200/4000 series springs to mind, let aloneB&Os VX-series of VHS machines. You will find practically nothing butleaking capacitors in these machines, particularly in the VXs where heat isa major problem and all caps have blackened pins from the boric acid inside running down.Often also staining the circuit board surface around the capacitor.Heat is not an issue in the Beocenters but the caps often leak the same way.
I've seen caps in TVs do the same and also in Penta amplifiers (and displays) and they are quite good quality builds.
Using a 63V rating capacitor in a circuit where the voltage across it nevergets higher than, say, 10 Volts or so is not always a good idea.The capacitor will not get "excited", it will relax and become "lazy", to put it inreader-friendly terms. You can reform it (take it out and slowly bring up its voltage) andit will often be able to live up again but it's not a lasting solution.Some of the early production individuals of the Beocord 6000/8000 series suffered fromthis, where the signal slowly faded out and became distorted in one or both channelsbecause capacitors with a too high voltage rating were used as coupling capacitors inlow-voltage amplifier circuits.
Martin
OK - all excellent comments and, one at a time:
Martin - once again, this proves that even without taking into account the stress (and there is) on the rubber seals, that there is a VERY CLEAR DIFFERENCE between the different types of capacitors, and one type will hold up very nicely for thousands of hours under conditions of high-stress (be it heat or ripple), and another will give up the ghost, after only a few hundred hours.
So what could cause a cap which on the face of it (105C, 2000hours according to the data-sheet) should last a few years, but didn't?
Answer - another uncounted stress factor, in this case, stress by the legs.
Many manufacturers state express warning to NOT bend the legs like this, so on this issue, I know that I do not, at all, stand alone.
One size does NOT fit all, be it speaker crossovers, signal or power circuits.
Johan - you are correct that ripple is the major cause of failure in PWM circuits, but here we see catastrophic failure after not 10+ years (like in the BeoMachines which Martin mentioned, and on which many of us have much experience), but after less than 1 1/2 years!
Anyway, just for the record, here is the comparison 22uF @120Hz between the Samwha RD (63V) and the Panasonic FM (50V), which is my first choice.
RD 105C 2000hrs - ripple capability 83mA
FM 105C 2000hrs - ripple capability 250mA x 0.55 = 137mA
So, IMHO, the Samwha RD is a piss-poor choice for this PWM circuit. But the tech chose it of his own free will, and charged the customer a not insignificant sum for his repair. The machine worked after the repair - no argument. But does that mean that the tech did his professional best? Not by a long shot.
Samwha, even though it's B&O's choice, will NEVER have a place in my workshop.
So, at the end of the day, it is the tech's absolute freedom to choose which components he wants to use, but blindly selecting for convenience, and not making a professional effort to select the best component for the circuit requirement, will only shortchange the customer.
Regardless of the discussion. I didn't know the brand Samwha. I only use the respected brands like Panasonic, Nichicon, Vishay etc. So I'm on the safe side then
Mostly using the 105 dgr with at least 2000 hrs...
Damages to capacitor seals are often done by to high soldering temps. or to long soldering time, all caps has a recommended soldering temp. and time. The most important part of soldering or desoldering is cleanliness, a clean soldering area lowers your soldering time. One failure that will be common for most of us is: Cleaning the area, desoldering the object, ordering spares, then waiting for delivery, after a couple of weeks the new parts arrive, and as one cleaned it all before desoldering, you would think its still clean, NOT so, copper (and other metals) starts oxidation as soon as oxygen gets to the surface, flush accelerate oxidation.
I always clean my soldering area with IPA, just before soldering or desoldering, this helps me to keep temp and time down.
I have done a lot of copper tube soldering lately, there one can see what happens with the solder tin used, leaving tubes cleaned just one day before soldering, made soldering slower or needed higher temp to get the solder to flow around the tube.
So: CLEAN CLEAN CLEAN
Collecting Vintage B&O is not a hobby, its a lifestyle.
Menahem,
you are right what you say about bending the legs of the caps. They must go straight out of the cap, there must be no angle, there must be 2x90 degrees for fitting to the board. The seals are stressed additionally and there will be sooner a problem. The cap is already damaged without using.
There is also an additional effect. Bending the wires in 2x90 degree angles to fit the board, makes less stress to the solder points. The cap can move and still does not crack the solders, it does not pull sideways.
There is no guarantee that someone will bend later a new soldered cap. The technician is working on the board, he must handle it, touch it. A cap soldered in without angling the legs will crack the solders, break off the copper wiring. There is a high risk damaging the board. There is also the risk, to pull the wires out of the cap.
Confirmed, ich have made exaclty the same experiences... and that the reason why i do it myself and i dont use Samwha. Crap caps...
There is also a reason not to use 63V caps if you dont need it: they are bigger and ventilation in a power supply is very important. Bigger caps make a problem here. That's also the reason, why i use miniature caps in the VX recorders... they last longer and stay coller, because better air flow.
Menahem, this is quite an interesting theory and usually while soldering components on a PCB, most technicians won’t care about this. I also believe that most capacitors might not have this issue anyways because of a better sealing though and I’m saying this because I have seen electrolytic deposits on the legs of capacitors which I had soldered straight into the PCB without any bend. This could be a consideration along with the quality of the rubber seal by the OEM.
electronic assembly manufacturing
This thread reminds me of an experience I had. In the early days of PC board mounted vacuum tube equipment, electrolytic capacitors failed early and often. Many of these failures were caused by cheap parts operated at or above their maximum ratings. But this was not always the case. It turns out that the method of mounting and installing the parts was responsible for many of the failures.
Back in the 70’s when I was doing repair I discovered another failure mode. There was a cathode bypass in the vertical output section (6LU8 tube) of most TV sets that failed about once a year. Even the replacement parts failed. I tried different parts, higher voltage parts, caps with more microfarads, they all still failed. They didn’t short out or go open, they just slowly developed a high internal resistance (ESR) that caused the picture to shrink from the bottom. In an effort to figure this out, I actually cut open some of the failed parts, and a good one for comparison.
Most radial leaded electrolytics are mounted directly against the board. They are then soldered from the bottom. As you are soldering the lead, it gets hot. When the lead gets hot it expands. The lead on a capacitor can grow a bit while it is being soldered. If the part is pressed down tightly to the board while it is being soldered, what is going to happen when the leads cool off and they shrink back to normal length? There is already a force built into the board design that is trying to pull the leads out of the capacitor. Now, the capacitor is on a circuit board right next to a hot tube. It gets baked every time the TV is turned on, and returns to room temperature every time the TV is turned off. This repeated thermal expansion and contraction will eventually tear the leads loose from the aluminum foil inside the capacitor.
The simple answer to this was to leave some space between the capacitor and the PC board. For most capacitors 1.5 mm is enough. When installing a physically small capacitor into a space meant for a larger cap leave longer leads, such that there is no stress applied to the part. If you pre – bend the leads, do not put any bend in the leads closer than 2 mm from the body of the capacitor. For large snap – in capacitors (no leads, fat prongs) this is not a problem, just insert them as intended and solder.
But this brought me to another problem I had to deal with. If you space your large leaded capacitors up from the board, as described above, they become prone to damage if the board is subject to excessive handling or drop. Since the part is now free to bend slightly, the leads can be torn loose from the bottom of the cap. I had a solution for that too. I placed a piece of thick foam tape across the bottom of the cap, with the leads protruding through it. This allowed room for thermal movement, and provides a cushion for the part. I used double sided tape as a solution, without peel the backing from the bottom. Some high quality capacitors already have a soft rubber cushion built into the bottom of the part, so that this step was not absolutely needed any more, but I still did it anyway. After putting the piece of tape on the bottom of the cap, I insert it into the board in the normal fashion. Pushing the cap in until it is flush with the board and bend the leads slightly to keep it there until I solder it. I used this method for every cap who lived next door to the GZ34 tube and some hot resistors.
"Believe nothing you read and only half of what you see, let your ears tell you the truth."
Oh yes the cathode by-pass capacitor failure! This does ring a bell or two! Your explanation is interesting Chris.
Jacques
Chris,
Very interesting about that contraction-expansion bit.
This is a really interesting thread. Certainly, in broadcasting when talking to technicians, i've always been lead to believe that PANASONIC make the best capacitors. Maybe this explains why their products seem to last forever with no problems! This is why Panasonic is the ONLY brand that I have total faith in. WHY? Because I know that their products last! I have a Panasonic 20 year old HiFi video recorder. Now this was used to record radio output. Along with 2 others, it was in use for 8 hours a day, using SONY E240 video tapes. After 10 years of use, I was given the machine. I still use it to this day and it's as good as day one!!! :)
Confirmed. Panasonic capacitors are probably the best quality available on the market. I have made the best experiencies with the blue-gold FC series und especially the low esr black type FR.
None of the defect hardware came back, but the customers did... and that is really good. :)
There are so many good caps, and many more bad one's. For the price is the Pana FR series indeed one of the best caps.
Especially for a valve amplifier in particular, it can be beneficial to give you a smidgin more HF. But I encountered not to overdo the use of electros with a low ESR. It gives me a exaggerated and fatiguing sound in long listening periods. However that's very personal, if you like what you hear, then I guess that's all that matters.
I would be very careful to use a capacitor like the FR in the bridge rectifier area of a good SS amplifier. Too low ESR could cause problems with the stability of the power supply. You have to look how was it is designed to tolerate wide ESR range, some may become unstable and oscillate.
Menahem, this is an interesting read and I believe that while soldering components on a PCB, most technicians won’t care about this. It also goes to say that the quality of sealing of capacitors might have a role to play in this as well. The cheap Chinese capacitors will quite easily be damaged through this soldering process. Having said that, I think all capacitors would eventually have leaked electrolyte if they are soldered like this.
printed board assembly