I just recapped a solid state phono preamp. Built in 1993, but new to me, it sounded fantastic before. However, I’ve seen what failed caps - both HV electrolytic filter caps and pressed paper couplers - can do to vintage gear. In my mind, the question regarding electrolytics in a power supply has always been not whether they will fail, but when. Clearly, I have nothing but disdain for the old “If it ain’t broke…” adage.
I replaced all 12 2200uF Panasonic M series, with 25V and 35V ratings, with Rubycon ZLH 2200uF/35V from DigiKey. With a 10000 hour lifespan and higher max temperature rating than the originals, as well as the added benefit(?) of lower ESR, they seemed a reasonable choice.
Aside from the recap itself, I disconnected both the hot and neutral lines at the IEC (with standard EMF filter) as well as the power LED leads at the separate preamp board to gain sufficient clearance to rotate the PSU board 90 degrees to get at the underside. Both were reconnected, but at the moment the LED is disconnected to rule out a short there (meter says there is not). Nothing else, including transformer leads, was disconnected.
After the soldering on the board was complete, I cleaned up both old and new flux residue with 91% isopropyl and a cotton swab. I’ve been unable to retrieve a few strands of cotton that were trapped by the cut leads.
The board itself is translucent white or “clear” Fiberglas with no solder mask.
Now, as soon as power is applied to the IEC (no power switch), the fuse immediately blows, leading me to believe there’s a short somewhere, but I can find no solder bridges, all the caps are aligned properly with respect to polarity, and all the cap leads have been trimmed.
I’m at a loss, and the only possibilities I can think of seem unlikely:
I’ve been DIYing for over 20 years, so I like to think I know how to handle an iron, but I admit I’m still getting the hang of my new Hakko. I seem to need higher temps than I think I should to get solder to flow well, but I can recognize when an iron is too hot.
I’m hoping that I’m missing something obvious. Thoughts, anyone?
I replaced all 12 2200uF Panasonic M series, with 25V and 35V ratings, with Rubycon ZLH 2200uF/35V from DigiKey. With a 10000 hour lifespan and higher max temperature rating than the originals, as well as the added benefit(?) of lower ESR, they seemed a reasonable choice.
Aside from the recap itself, I disconnected both the hot and neutral lines at the IEC (with standard EMF filter) as well as the power LED leads at the separate preamp board to gain sufficient clearance to rotate the PSU board 90 degrees to get at the underside. Both were reconnected, but at the moment the LED is disconnected to rule out a short there (meter says there is not). Nothing else, including transformer leads, was disconnected.
After the soldering on the board was complete, I cleaned up both old and new flux residue with 91% isopropyl and a cotton swab. I’ve been unable to retrieve a few strands of cotton that were trapped by the cut leads.
The board itself is translucent white or “clear” Fiberglas with no solder mask.
Now, as soon as power is applied to the IEC (no power switch), the fuse immediately blows, leading me to believe there’s a short somewhere, but I can find no solder bridges, all the caps are aligned properly with respect to polarity, and all the cap leads have been trimmed.
I’m at a loss, and the only possibilities I can think of seem unlikely:
- the isopropyl damaged the board
- I damaged the IEC internal filter components with excess heat
- I damaged the new caps while soldering
- Low ESR is causing current to surge initially
- Bad karma/juju
I’ve been DIYing for over 20 years, so I like to think I know how to handle an iron, but I admit I’m still getting the hang of my new Hakko. I seem to need higher temps than I think I should to get solder to flow well, but I can recognize when an iron is too hot.
I’m hoping that I’m missing something obvious. Thoughts, anyone?
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Those Pana caps were fine, and surely would last another decade or two.
You've "bought into" the "recap" stuff, and now have problems.
Sometimes, it's best to leave well-enough-alone and ignore that idiotic cap replacement disease that has infected the population.
As for an answer to your problem, and being a professional service tech for 45 years, the issue could be just about anything that you've done to it, and certainly not easily determined across the internet.
You might have installed a cap in backwards for all I know.
But I dislike having to speculate things.
It is alway possible that the silkscreened component layout is incorrect. I always check the polarity of existing capacitors as I take them out and mark the board, just in case the labelling is wrong. A reversed capacitor can blow a fuse. It's also possible you have bridged across two tracks somewhere and you just can't see it - it may look like it is meant to be the way it is. Also look for a solder splash on the IEC.
If you have a variac you can raise the mains voltage slowly, or even keep it low at, say, 20 volts while you probe around the circuit board. Otherwise a 'dim bulb' tester lead with a suitably small wattage globe in it may allow you to safely apply power. If ypu can't apply any (even tiny) voltage without excess current, the fault is likely on the mains side of the power supply.
If you have a variac you can raise the mains voltage slowly, or even keep it low at, say, 20 volts while you probe around the circuit board. Otherwise a 'dim bulb' tester lead with a suitably small wattage globe in it may allow you to safely apply power. If ypu can't apply any (even tiny) voltage without excess current, the fault is likely on the mains side of the power supply.
Not sure this particular substitution will bring any sonic benefits, but what's done is done 🙂
Hard to tell what you did wrong without pictures. You can start troubleshooting by testing the resistance of your B+ line with respect to ground, then test the rectifiers with a diode check. Do you have a variac?
The thing is.....there is intelligent "preventative maintenance" of products, and than there is internet-driven paranoia, which can lead to problems.
Being in the Service Industry for a long time, I can honestly say that it's unecessary to go about replacing electrolytic caps in things just because you've "heard" that its a good thing to do as "advised" by the internet goonballs.
These people are clearly not technicians of any merit, because if they were, they would not promote such nonsense.
This trend has as I see it, become a disease of sorts, and led to many problems that never should have reared their ugly heads in the first place.
Yes, capacitors can fail, and yes they can cause issues, but diving into products with a blind sense of concern and experience will cause threads like this to be posted.
What I've noticed, since the early/mid 2000's is the increase of this "disease" about "recapping" due to that "Bad Caps website" which addressed the concerns over a batch of electrolytics made by a company that had a stolen electrolyte formula that was missing a key ingredient, causing premature failure.
These capacitors were used in many products, including NASA and Military equipment, medical equipment, and computers, along with hoardes of consumer products.
Word spread like wildfire about this, thanks to the internet and its plethora of blabbermouth posters and self-made guru's.... and this is the result.
Paranoia....!
Prior to this "bad caps" fiasco, it was not an issue, and in my repair shop over the decades, and even today, I only occasionally had to replace failing capacitors.
Tens of thousands of pieces of customer's equipment came through my door for service, and repairs were primarily to abuse, carelessness, and in some cases, age-related normal wear.
And yes, I've had the occasional customer walk in and demand that their equipment be "recapped", but these customers interestingly enough only started showing up in the mid-2000's - and I suspected immediately that they had the internet-driven paranoia diease.
I would hope that this post will enlighten others, and spread around enough to quell this nonsense about messing with their equipment.
Being in the Service Industry for a long time, I can honestly say that it's unecessary to go about replacing electrolytic caps in things just because you've "heard" that its a good thing to do as "advised" by the internet goonballs.
These people are clearly not technicians of any merit, because if they were, they would not promote such nonsense.
This trend has as I see it, become a disease of sorts, and led to many problems that never should have reared their ugly heads in the first place.
Yes, capacitors can fail, and yes they can cause issues, but diving into products with a blind sense of concern and experience will cause threads like this to be posted.
What I've noticed, since the early/mid 2000's is the increase of this "disease" about "recapping" due to that "Bad Caps website" which addressed the concerns over a batch of electrolytics made by a company that had a stolen electrolyte formula that was missing a key ingredient, causing premature failure.
These capacitors were used in many products, including NASA and Military equipment, medical equipment, and computers, along with hoardes of consumer products.
Word spread like wildfire about this, thanks to the internet and its plethora of blabbermouth posters and self-made guru's.... and this is the result.
Paranoia....!
Prior to this "bad caps" fiasco, it was not an issue, and in my repair shop over the decades, and even today, I only occasionally had to replace failing capacitors.
Tens of thousands of pieces of customer's equipment came through my door for service, and repairs were primarily to abuse, carelessness, and in some cases, age-related normal wear.
And yes, I've had the occasional customer walk in and demand that their equipment be "recapped", but these customers interestingly enough only started showing up in the mid-2000's - and I suspected immediately that they had the internet-driven paranoia diease.
I would hope that this post will enlighten others, and spread around enough to quell this nonsense about messing with their equipment.
It does depend to a certain extent on what exactly it is that tickles your pickle.
I wouldn’t recap a piece 90’s era line level audio gear unless it looked like the whole piece of equipment had been baked half to death. Rackmount PA gear in general, for example, often have been subjected to very high average heat and need recapping from nose to tail. I’ve repaired a couple of crown power amps recently where the main filter caps actually rattled when shaken and these amps are under ten years old.
My dad likes his valve gear, much of which is older than you are, and that’s another case recap before you power up.
I personally love high end and exotica from the 60s and 70s and then again, pulling and measuring the individual caps has shown me that it’s generally worth goi g through the unit and the period grey, blue and black Elna and United chemicon cpas they used in that era.
Same goes for the lower value, orange, low leakage caps. For some reason the 2.2uF ones of these last forever whereas the the lower and higher value ones seem to develop leaks, relatively speaking.
It makes an audible difference run my experience, in those cases.
The Panasonic M series has a guaranteed expected life of 2000 hrs when operated at the maximum 85 deg C. The spec sheet says that this expected life is doubled for each 10deg C reduction in operating temp. I would expect a phono preamp to operate not far above ambient say 30deg C at the maximum. So expected life will be 2000hrs x 5.5 or about 11000 hrs so plenty long enough not to warrant preventive maintenance changes.
There is one caveat though in the data sheet that says expected life cannot exceed 15years due to aging of rubber seals.
One possible cause of your fuse blowing might be the IEC mains filter. Some older Schafner ones particularly are prone to failure due to failure of the X type caps used.
It seems their plastic cases crack over time and let in moisture. Maybe your soldering has disturbed it. Try powering up without it.
There is one caveat though in the data sheet that says expected life cannot exceed 15years due to aging of rubber seals.
One possible cause of your fuse blowing might be the IEC mains filter. Some older Schafner ones particularly are prone to failure due to failure of the X type caps used.
It seems their plastic cases crack over time and let in moisture. Maybe your soldering has disturbed it. Try powering up without it.
With 1950's valve equipment it often (definitely not always) suffices to reform the main supply electrolytic capacitors by very slow charging rather than to replace them. Besides, the paper capacitors are almost always leaky, and some of those can cause consequential damage.
Anyway, if there is a hard short in the equipment now, maybe forcing a DC current through the mains input (small enough not to blow up the fuse) and measuring voltage drops could help locate it. There should be voltage dropping across the wires from the mains input to the short and practically no voltage in wiring behind the short.
Anyway, if there is a hard short in the equipment now, maybe forcing a DC current through the mains input (small enough not to blow up the fuse) and measuring voltage drops could help locate it. There should be voltage dropping across the wires from the mains input to the short and practically no voltage in wiring behind the short.
Unless it's older than 68 years, I'll agree to that.
Nevertheless, I've done customer's "Restorations" of vintage radio, etc, stating back to 1929.
Family heirlooms stuff.
Can you post a picture? If not try removing one cap at a time. I would bet you have either installed a cap backwards or one of the new caps is bad. Almost guaranteed it is something you did.
What I would do is to use a Variac (adjustable AC power source) and apply a low AC voltage, like 10Vac or so to the AC power cord of the device, turn it on, and then with a DC voltmeter, probe the polarized caps and see if the polarity of the voltage is correct at each cap as given on the cap's markings. Correct any that are backwards, and if the PCB is marked wrong, correct that too with a marker. The idea behind doing it this way is that the electrolytic caps can withstand a very low backward-polarity DC long enough for you to determine that any are wrong. Discard any backward cap you may find and use a new one as a replacement. Discard the old cap, poor abused thing.
I've just recapped an exceedingly hot-running class-A power amp that's only 12 years old. The 85C-rated caps were down to ~60% capacitance at working frequency; I've also tested a late 1960s A/B integrated whose original electrolytics were 100% perfect after 50 years use; recapping should always be case-by-case.
As to OP's problem - once actual shorts have been systematically-eliminated - is it simply possible that the fuse was always rated with negligible margin, and perhaps the new caps draw more current, more quickly, than the old ones did? Is the fuse F or T-rated? Sometimes the same current rating but a slower acting type will hold on startup.
As to OP's problem - once actual shorts have been systematically-eliminated - is it simply possible that the fuse was always rated with negligible margin, and perhaps the new caps draw more current, more quickly, than the old ones did? Is the fuse F or T-rated? Sometimes the same current rating but a slower acting type will hold on startup.