Author Topic: Check your RIFA caps in your Agilent bench power supplies and lessons learned  (Read 2782 times)

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Offline NoisyBoy

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If you have Agilent/HP bench power supplies, open them up and check/replace your RIFA X2/Y caps!

While I was trouble-shooting a random problem with my 6643A system power supply (delivered in late 2007), I decided to also inspect the RIFA caps.  While the four larger caps on A1 main board were fine, I noticed small cracks on three of the small Y2 caps on the A1 main board and the GPIB board. 

Knowing the risk associated with the RIFA caps, it led me to a quest of opening up all my bench power supplies to check the status of the RIFA caps. 

Of the three Agilent 3615A I ordered in 2012 for their silent operation, 2 of them showed nearly invisible cracks on the X2 caps.  It is very hard to see, it only shows when the light is hitting it the right way.

Of my first and oldest supply, it is a HP branded 6632A dated to 1993, there were visible cracks on all 5 of the RIFA caps. 

I ended up replacing all the RIFA caps on each supply and recalibrated each of them to spec, so I can have a common base line across them.  I also recapped all electrolytic caps on the 6632A with highest grade Nichicons due to its age.  Amazingly, none of the electrolytic cap I replaced showed any sign of bulging or leakage, and every one was right-on in spec after checking for capacitance, D, and ESR after 26+ years.  I pulled up the spec of the larger Sprague caps made in the US, they were rated for 12000 hours lifespan.  It is a testament to the quality of the HP construction, so I am leaving the non-RIFA caps alone in all my Agilent branded power supplies. 

So my lesson learned, replace all older RIFA caps for sure, check the status of newer ones.  For electrolytic caps, I don't think there is reason to change them based on time alone unless I am seeing other issues, as the ripple and accuracy for every supply are all well within spec. 
 
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Offline Hexley

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Case in point: this RIFA capacitor failed two weeks ago in my HP 6236B triple power supply. The lab bench still smells slightly of burnt phenolic compounds. :-(

The supply has 1978 date codes on its parts, so the RIFA cap had a good run.

[Edit: fixed image size.]
« Last Edit: January 25, 2020, 07:01:02 pm by Hexley »
 

Online PA0PBZ

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Just change the title to "check your RIFA caps", they are everywhere waiting to detonate. This is from a Tek scope, took me a while to find all the pieces:

[attachimg=1]
Keyboard error: Press F1 to continue.
 

Offline SeanB

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Not only RIFA fail, I sort of unpotted a Corcom mains filter that failed, and inside the tar there were some paper capacitors that had failed, along with some hard to read white polyester capacitors ( tar really covers stuff, and I was getting a little tired of the smoke cooking it out over the gas stove) that provided the class Y stuff. The X ones were all somewhat leaky, at least they were not happy with 500VDC applied from the insulation tester, and had tripped the mains as well during the going out phase.

Replaced with another younger mains filter, donated by a scrapped LG plasma TV that was the victim of lightning killing the main board. PSU might have survived, the set was the main earth connection, while the rest was all class II insulated stuff, so the close hit around 1km away cooked it via the HDMI input. Filter definitely survived, it has no earth choke to blow open.
 

Offline babysitter

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RIFA are so reliable bombs, from the smell and description alone I diagnosed the exact problem of a Kenwood kitchen machine last saturday at the repair cafe, impressing everybody.
(Myself I had 2 "exploding", exchanged around 5 as preventative measure at home)
I'm not a feature, I'm a bug! ARC DG3HDA
 

Online TERRA Operative

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I replace these on sight, I don't care how ok they may look. It's not a matter of if, but when they'll go bang.
Any circuit design must contain at least one part which is obsolete, two parts which are unobtainable, and three parts which are still under development.

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Offline TK

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I had an HP DC power supply that had a RIFA cap on the mains input.  It just exploded the other day while it was plugged, but switched off.  Fortunately I unplugged it and ventilated the room before it caught fire.  Scary...
 

Offline NoisyBoy

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Yike, even with all new caps, my bench power supplies are on a secondary power strip even after I turned the power on for the bench.  In my case, luckily I don’t own anything else with RIFA caps.

I changed some of them to WIMA caps and TDK caps, but a few stayed Kemet RIFA due to its unique lead spacing, including all the X2.
« Last Edit: January 27, 2020, 04:57:39 pm by NoisyBoy »
 

Offline Gyro

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They actually have some superior characteristics in across the line applications - particularly in dV/dt withstand, which is superior to MKPs. They just don't age (at all) gracefully.
Regards, Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline Vovk_Z

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Just change the title to "check your RIFA caps", they are everywhere
+1. Rifa caps at Tectronix 24xx series are well-known too (I have changed them all).
 

Offline bd139

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Buggers aren’t they. The  above exploded in my old PM3217  :--.  My current PM3217 had one go off in it that the previous owner appears to have replaced.

They’re a regular feature on the TEA thread spawning this  :-DD



On top of this we have Schaffner mains filters which are basically three RIFAs and a common mode choke inside a pipe bomb  :-DD
« Last Edit: January 28, 2020, 10:21:36 pm by bd139 »
 
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Offline Electro Detective

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I replaced one that bonged out of a 30 yo? kitchen appliance, and what a smell and stubborn ass to clean up  |O

Actually the appliance worked fine with no Reefer? installed for a few days, with no switching or running interference,
or RCD trips.  :phew:

Still I sourced and fitted a Jaycar equivalent value and appliance works like a new one again


Do these things die solely from use, age or a combo of both ?

and is there a 'one size fits all' value to stock up on, as I'm certain a LOT of gear here has dud/aging spliffs Reefers Rifas fitted

Solly for my bedingleesh  :D

 

Offline bd139

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Yeah my mother did that. The one in her 1980s food mixer exploded. Smoke came out and all sorts. But it still worked so she just carried on using it. There's probably some ham up the road shaking his fist at the sky now :-DD

As for failure, the original ones had an epoxy case which degraded over time and let moisture in. Also they are "sacrificial" capacitors so the dielectric gets punched through by any transients. Eventually they either get damp and explode or burn up. Basically they have a design life and a lot of the equipment we use exceeds that considerably!

Really they are excellent capacitors. When I remove a RIFA I put a new RIFA back in again. A sticker goes on the back "replace RIFAs by XXXX" for the next person to come along.

 
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Offline Gyro

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The reason they are so susceptible to moisture after the epoxy cracks is that they are metallised paper, not plastic film. The metallised paper construction is also responsible for their high dV/dt rating though. Swings and roundabouts.
« Last Edit: January 29, 2020, 12:08:44 pm by Gyro »
Regards, Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline babysitter

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But to restore some honour and possibly quench the substrate for myths, they produce smell and tar, but should never be able to set fire to the FR rated electronics stuff around them. Right? Right?
I'm not a feature, I'm a bug! ARC DG3HDA
 
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Offline NoisyBoy

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It is difficult to have a one size fits all for RIFA cap. I have 3 different lead spacing in my supplies based on cap size, being all main connected, you don’t want any extra length leads exposed.  All replacement caps are soldered right on to the board with no gaps exposing leads. 

I also put on a sticker on my equipment, showing what caps, and when they were replaced, as well as the calibration date.  So I can find out the state of the equipment without opening them.

Depending on how well your equipment manage cooling, based on my observations, you can probably go 10-15 years without issues.  The ones on my 25+ years old 6632A are all cracked but luckily none had failed yet.  On my 6643A, only the smallest Y cap showed small cracks, the larger ones, as well as the big X2 were all perfect (I replaced them anyway).  So there is a chance that the small Y class caps are most susceptible to cracks, the bigger ones may take longer. 
 

Offline Electro Detective

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re 'One Size Fits All'
The clapped out Rifa I replaced was soldered up with with a resistor and blue disc style capacitor in a 'factory fitted bodge' arrangement,
and into/across the three way mains terminal inside the vintage yellow 'white goods' appliance.

Basically any size RIFA and lead spacing/gauge/thickness would work in that situation

The cap and resistor looked, tested and checked perfect so I re-used them.

Mine was a 240 volt application btw, not 120 volt,
I assume there are two international voltage type Rifas ?
Can the 120 volt ones be series'd up to do 240 volts? =  :-// x2

 

Offline NoisyBoy

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For any caps, I would never go below the voltage of the one I replaced, it is OK to go higher, but never lower.

All the RIFA X2 caps in the Agilent supplies are rated for 250V, so my guess is you are probably safe to get one that is 250V or higher.
 

Offline Scratch.HTF

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I saw a Rifa X class capacitor (which was opaque white) fail right in front of me.
RIFA: Ready In Failing Anytime
If it runs on Linux, there is some hackability in it.
 
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Offline Alex P

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If you have Agilent/HP bench power supplies, open them up and check/replace your RIFA X2/Y caps!
...
Thanks! I checked my HP E3630A power supply (1995-ish) and found and replaced a Rifa X2 cap (cracks visible).
 

Offline NoisyBoy

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Great, my 6632A is from similar era, all the RIFA caps in it are cracked.  I think the fact my home lab is humidity controlled year-round is perhaps what keeps it from disaster. 

I believe most E36XXA supplies have a single X2 RIFA cap across the main that is connected regardless of whether it is turned on or not.  So it is always a good idea to check and replace them.

 

Offline Helix70

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Thanks for the tip.

I have just checked my 34401A multimeter, my 6612C System DC Power Supply, my 33120A Function Generator, and my 5135A Universal Counter and none of them have RIFA caps or Schaffner filters. I provide this information as a reference for others who may have the same gear.

No other signs of any leakage or deteriation on the electrolytics either.
 


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