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Old 12-28-2019, 05:09 PM   #101
momaka
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Default Re: How to Recondition (Reform) Electrolytic Capacitors and Why

^ The MOSFETs won't get damaged, but depending on the motherboard, other things might. Case in point, some older AMD and Intel boards from the early and mid-2000's used the CPU V_core also for the chipset (example: Intel Pentium 4 Northwood motherboards with i845 chipset). So in those cases, you'd be feeding a high voltage into some chip that shouldn't be.

With most PSUs, though, I think it should be possible to feed voltage on the output rails to reform the caps. Sometimes I back-feed 12V in my ATX PSUs to run tests on the fan controller circuit.
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Old 03-14-2020, 04:02 AM   #102
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Default Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Hi all, I wrote here as I think it's better than open a new topic. My apologies if it isn't so...
I have to restore a very old guitar amp, trying to get it as close as possible to the original. The circuit is very simple and used only one triple electrolytic cap branded "Planet" model CTC-306 (from the '50 or so, I suppose) wich in a past repair was excluded from the circuit and replaced with three new capacitors. The amp works fine.
I tested the cap with an analog oscilloscope component tester and all thre sections show a very high ESR, even if the capacitance seem to be ok. I didn't put voltage on and think it had no voltage for more than 20yrs or possibly more...
The cap housing is made of paper, and I think that the hig ESR is due to dried out elecrolyte... If this was the case, I'm afraid the cap regeneration would fail...
Now, the big question: is there some way to regenerate the electrolyte (wich would be some sort of wet compound)?
I will try regeneration, anyway... I've seen that in case of unrecoverable cap one solution to keep it "original" is to pull out everithing and hide new caps inside, but would do as last chance...
Any other idea?
Thaks in advance.
Greetings from Italy
Giampietro
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Old 03-19-2020, 06:16 PM   #103
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Default Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Quote:
Originally Posted by giampi View Post
I tested the cap with an analog oscilloscope component tester and all thre sections show a very high ESR, even if the capacitance seem to be ok. I didn't put voltage on and think it had no voltage for more than 20yrs or possibly more...
The cap housing is made of paper, and I think that the hig ESR is due to dried out elecrolyte... If this was the case, I'm afraid the cap regeneration would fail...
Now, the big question: is there some way to regenerate the electrolyte (wich would be some sort of wet compound)?
Unfortunately, no.
I'm not very knowledgeable on old gear and caps, but from what I've read, old paper caps like that have a finite shelf/useful life, as do all "wet" electrolytic caps. Given their age, they are just due for replacement. There is nothing you can do to regenerate the electrolyte. And with their high ESR, chances are nothing will happen even if you do try to "reform" them with a voltage, because more than likely, they have gone "dry" (i.e. electrolyte evaporated or disintegrated or both.)

Quote:
Originally Posted by giampi View Post
I will try regeneration, anyway... I've seen that in case of unrecoverable cap one solution to keep it "original" is to pull out everithing and hide new caps inside, but would do as last chance...
If you are trying to keep looks the exact same way, then that's probably your best bet.

I personally don't see anything offensive about old gear with new parts inside (As long as it's done sensibly, of course.) Shows that even the old stuff that's built like a tank won't last forever and needs periodic "updating" on certain components.
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Old 06-30-2020, 04:23 AM   #104
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Default Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Hi, can you show me some simple schema for reform 2000uF/400V Sprague caps?
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Old 06-30-2020, 02:01 PM   #105
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Default Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Read post 1 & 2, you will also need high Voltage power supply. What do you have?
https://www.qsl.net/g3oou/reform.html
https://www.nmr.mgh.harvard.edu/~reese/electrolytics/
http://www.electrojumble.org/reforming.htm
http://www.angelfire.com/electronic/...store_cap.html
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Old 06-30-2020, 03:19 PM   #106
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Default Re: How to Recondition (Reform) Electrolytic Capacitors and Why

ok
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Old 06-30-2020, 03:22 PM   #107
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Default Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Once you read those information then you will understand the concept then you can apply it to your need.
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Old 07-02-2020, 08:50 PM   #108
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Default Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Quote:
Originally Posted by AmidzaDado View Post
Hi, can you show me some simple schema for reform 2000uF/400V Sprague caps?
Probably the easiest thing to do would be to rectify mains (230/240V AC) with a full bridge rectifier, then connect each Sprague 2000 uF, 400V cap, one at a time only, to the DC output of the bridge rectifier. To limit current, use a 10-25 Watt wall-type ("regular") soldering iron and connect in series with the AC live and your bridge rectifier circuit.... i.e. similar to this:

AC live ----> 10-25 Watt soldering iron ----> full bridge rectifier ----> 2000 uF, 400V cap
AC neutral -------------------------------> full bridge rectifier ----> 2000 uF, 400V cap

A 25-Watt soldering iron (or heating element of equivalent power rating) made for 230/240V AC line will have about 2 KOhms resistance, more or less, which is perfect for charging large HV caps without overheating (it's a soldering iron made for 230V AC, after all. )

If you do build this circuit, beware of live/dangerous voltages, of course. And keep in mind your reformed caps will be charged to about 360-370V DC. As such, take good precautions to discharge them carefully and gracefully (using your 10-25W soldering iron to connect across the + and - terminals on the caps after they are reformed and removed from the reforming circuit should discharge them safely.)

Last edited by momaka; 07-02-2020 at 09:36 PM..
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