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Electrolytic Capacitor questions
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Joule Thief:
I am in the process of repairing a HP 6237B triple output power supply ( 0.5 volt ripple on ALL outputs).

The problem seems to be centered around a dried out metal can electrolytic cap in the REF and BIAS supply. 13 volts of ripple on the cap is not helping.

My question is in regards to the value of this capacitor. The value is marked as 490uf at 85 volts. Why would the design spec out 490uf when 470 uf would be a more common value? Is it possible 470 was not available in an appropriate form factor and a 490 cap was available ?  I can't believe 20uf would make a difference in the circuit performance.

c4757p:
Typical HP, they used all sorts of bizarre capacitor values. Just use 680uF :P
SeanB:
470uF 160V is a common value, and will likely fit as well. The only reason HP used odd values was because they made the capacitors themselves, or were buying enough to specify a value that was the maximum a manufacturer could stuff into a can.
Hydrawerk:
What is this capacitor? Is it a RD series from Samwha?
http://www.samwha.com/electric/product/list_pdf2/RD.pdf
Electro Detective:

Buy a handful of assorted (not in a packet) 470 uf caps from a local electronics parts shop, and I'll bet one or two of them will kick in at 490 uf

or... if you're in good with the staff and or a regular customer (like me  :-* ) bring in a cap tester/multimeter and explain what the deal is, and they usually say ok
and may help you sort some out too on the counter if the shop isn't busy

Best to go when it's the slow part of the day and the staff aren't 'multitasking'  :blah: |O :rant: :horse:

FWIW: I discharge/short the unsuitable value caps after testing, before returning them to their spot in the shop

I do the same test biz with resistors and potentiometers when I need a freaky value or matched pairs/quads etc

It saves time, money, online purchase headaches, keeps the shop in business

and fellow electronerds in a job  :-+ :-+

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