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RIFA caps in Tektronix 4404

Elektraglide

Elektraglide

Experienced Member
Joined
Mar 24, 2023
Messages
53
Location
UK
Hi,
I can find replacements for the 0.1uF and 0.022uF Rifa caps in the PSU, but it also has a 0.5uF + 22 Ohms Rifa. I can see through the epoxy (?) there is a 22 ohm 1 watt resistor in series. I cannot find such a thing, do I just buy 0.47uF and add a 22 Ohm resistor?

Adam
 
Thanks - that looks like the stock part. Should I avoid using RIFA caps? Are they intrinsically "bad" - everyone seems to say rude things about them!
 
There is nothing wrong with new ones that are currently in production, I use them from time to time. The problem is that the 30+ year old ones suffer from the cracking plastic case due to shrinkage of the material (moisture ingress makes them heat up and explode) which is why even new old stock is to be avoided.
I hope that KEMET changed the formulation of the plastic so it won't be a problem in 20-30 years from now.
 
All recapped but waiting for some other bits. The old PMR209 was looking pretty knackered with some scary cracks..
The eletrolytics weren't bulging and 'looked fine' but I replaced them anyway.

recapping.png
 
Fun footnote. Resistance testing the RIFA caps, only the large one with the scary cracks works - the smaller ones with no visible marks, are all faulty.
 
What did you try to measure exactly? The uncracked RIFAs should still be within spec...

The electrolytics, if they're fine I would keep them. I only change them if they're out of spec, physically broken/leaking or it's a series known for failing.
 
powerlot said:
What did you try to measure exactly? The uncracked RIFAs should still be within spec...

The electrolytics, if they're fine I would keep them. I only change them if they're out of spec, physically broken/leaking or it's a series known for failing.
Click to expand...
Just measured resistance. Majority of the Rifa *reduced* resistance over time - not sure what that means. (?)
And yes, all 6 electrolytics show monotonic increasing resistance to +inf. I'll keep them as suggested.
 
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