Topics

7603 filter caps - ripple voltage and Adapters

tinkera123
 

Hi,

One of my 7603 Mainframes died .... tracked the problem to a filter cap in power supply, C821 ... removed it, (Sprague 18,000uF 15vdc).
Scope is up and running again with a junk box, smaller uF 16v electrolytic tacked into pcb.

My questions ... proper replacement cap(s)? .... only one or all Main powerboard caps (7of)? .... Capacitor Adapters for 'snap in' caps??

In searching this Forum, I found references to EPCOS, Nichicon and Panasonic brands being used. Selecting capacitance and voltage rating is not a problem, but I would like some guidance as to the Ripple voltage rating issue. For example, this web site .... http://www.farnell.com/datasheets/2280821.pdf .... is for the EPCOS B41252 series of electrolytic caps. I am not sure how to interpret the Ripple current data eg Page 8, I am assuming that the columns headed Iac,max Iac,R are the ripple currents at various temperatures ....
Is this correct??
How do I interpret these numbers??
Are these Ripple currents adequate / above adequate for this power supply??

Does your experience suggest replacement of just the dead cap?? or replacement of all 7 filter caps on this Board??

Capacitor Adapters ... https://www.ebay.com.au/itm/Capacitor-Adapter-Tek-Tektronix-7000-Series-Recap-6-square-1-triangle-adapter/272799971348?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 ....
seem like a neat way to do the job. Anyone had any experience with these Adapters?? Is 'snap in' reliable??

Thank you,
Ian

Stephen Hanselman
 

Contact me off list. We have cap adapters for several of the styles of “can” caps. If you can get a picture of top and bottom with a ruler on the bottom side so I can get a sieve reference

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Sep 7, 2019, at 04:01, tinkera123 <@tinkera123> wrote:

Hi,

One of my 7603 Mainframes died .... tracked the problem to a filter cap in power supply, C821 ... removed it, (Sprague 18,000uF 15vdc).
Scope is up and running again with a junk box, smaller uF 16v electrolytic tacked into pcb.

My questions ... proper replacement cap(s)? .... only one or all Main powerboard caps (7of)? .... Capacitor Adapters for 'snap in' caps??

In searching this Forum, I found references to EPCOS, Nichicon and Panasonic brands being used. Selecting capacitance and voltage rating is not a problem, but I would like some guidance as to the Ripple voltage rating issue. For example, this web site .... http://www.farnell.com/datasheets/2280821.pdf .... is for the EPCOS B41252 series of electrolytic caps. I am not sure how to interpret the Ripple current data eg Page 8, I am assuming that the columns headed Iac,max Iac,R are the ripple currents at various temperatures ....
Is this correct??
How do I interpret these numbers??
Are these Ripple currents adequate / above adequate for this power supply??

Does your experience suggest replacement of just the dead cap?? or replacement of all 7 filter caps on this Board??

Capacitor Adapters ... https://www.ebay.com.au/itm/Capacitor-Adapter-Tek-Tektronix-7000-Series-Recap-6-square-1-triangle-adapter/272799971348?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 ....
seem like a neat way to do the job. Anyone had any experience with these Adapters?? Is 'snap in' reliable??

Thank you,
Ian


Gudjon Gudjonsson
 

Hi

My questions ... proper replacement cap(s)? .... only one or all Main powerboard caps (7of)? .... Capacitor Adapters for 'snap in' caps??

In searching this Forum, I found references to EPCOS, Nichicon and Panasonic brands being used. Selecting capacitance and voltage rating is not a problem, but I would like some guidance as to the Ripple voltage rating issue. For example, this web site .... http://www.farnell.com/datasheets/2280821.pdf .... is for the EPCOS B41252 series of electrolytic caps. I am not sure how to interpret the Ripple current data eg Page 8, I am assuming that the columns headed Iac,max Iac,R are the ripple currents at various temperatures ....
Is this correct??
How do I interpret these numbers??
Are these Ripple currents adequate / above adequate for this power supply??
The definitions can be found here:
https://www.tdk-electronics.tdk.com/download/173614/7a48c67d03577cfbbfc9d186c6e257dd/aluelko-industrial-snap-in-pb.pdf

I did recap one of my 7603 recently without checking the max ac
current but none has blown up yet :)
I used a self made PCB that uses snap in capacitors and has holes to
fit both Tektronix capacitor types and I believe I can use them in
my TM-503 as well. The gerber files are free for anyone interested.

Regards
Gudjon

tinkera123
 

Thanks for responses Stephen and Gudjon .....off list responses sent.

--
Cheers,
Ian,
Melbourne, Australia

Roy Thistle
 

On Sat, Sep 7, 2019 at 04:01 AM, tinkera123 wrote:


the Ripple current data
Yes, I take Iac,max, to be the maximum ac ripple current, at the listed temperatures (across the table header row), for the B41262, 105 degree C rated capacitors. The R in the Iac,R refers to "reference"... I thinks it's used somewhere, as a parameter, in the engineering equations.
Everything else being equal, you could take the ripple current as being twice the load current, but, that's very approximate.
If someone has an old Sprague catalog, maybe you could match the ripple current of the replacement to the Sprague one.
Nichicon and Panasonic brands are reputed to be good.
Everything else being equal, heat is the biggest enemy of Aluminum electroytics, both external (ambient), and internally generated heat.
Assuming the same ambient heat, and a good manufacturer, if you choose a higher temperature rated capacitor (say 105 C, or higher, relative to 85 C)... then the game says you will get better life, and less failure; but spend more money. The caps should be more heat tolerant, and live longer.
replacement of just the dead cap?? or replacement of all 7 filter caps on this Board?
Well how long have they been cooking in there for? As I recall the 7603 has a pretty compact linear power supply, with the transformer near those filter caps, to help cook them. You could measure the capacitance and esr, in circuit... maybe. Once you take them out to measure them... seems like... unless you're ultra cheap like me... seems like a waste of time to solder those old ones back in again. You could replace the bad one and look to see if the ripple is in spec. If you are operating the 7603 (or it has been operated) for long on periods, or in a "hot" location, or clogged up fan... maybe the other filter cap(s) are cooked out, or will cook out too, relatively soon.. or maybe not. For me, I don't like "operating" on a circuit board, unless I have to.

tinkera123
 

Hi Roy,
Thank you ....

Nichicon and Panasonic brands are reputed to be good.
Everything else being equal, heat is the biggest enemy of Aluminum electroytics,
replacement of just the dead cap?? or replacement of all 7 filter caps on this Board?
Re Panasonic and Nichicon .....for that reason I was comparing Panasonic to EPCOS datasheets .... and as best as I understood how to, I found that at same uF, Temp, Voltage etc, there was little difference in Ripple current capability ... but my knowledge and experience here is thin.
Decided to go with the EPCOS caps as I can get a full set of them, in Australia, in about 1 week. I will re-cap the whole PS board (7 electrolytic caps) and measure the Ripple current ..... when loaded ... and see how that compares to the datasheet. I will also test the other caps when I get them out of the board.

Cheers,
Ian,
Melbourne, Australia