Re: HP 83595A Repair Advice
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Hi Mark,
Glad to help, hope you get it up and running soon. Just guessing here, but maybe your A6 board has at some point been next to another A5 board where a tantalum capacitor has decided to become a rocket engine.
I'm also looking for a reasonably priced plugin for my 8350 / 8757 combo that go higher in frequency than my current one, 8.6GHz 83525A-H03. But I'm in Norway, and usually what I find on ebay does not ship here, or the shipping is very high. I'm not in a hurry, so I will just keep looking.
Regards, Askild
On Sat, Feb 25, 2023 at 7:19?PM Mark Bielman < mbielman@...> wrote:
Askild,
You were right! That cap is clearly bad. And the associated inductor looks damaged as well.
Surprised I missed it. Not sure how the black stuff made its way to where it did.
New parts ordered and on the way.
Thanks!
Mark
Hi Mark,
Yes, the one just next to the orange tantalum.
Just measure them with an ohm meter. Usually they will be short circuit or very low ohms if they are bad.
Regards,
Askild
On Sat, Feb 25, 2023 at 1:42 AM Mark Bielman < mbielman@...> wrote:
Hi Askild,
Do you mean the brown one? (left of the inductors)
There are many of these and are different values (and color) than the orange ones.
Also, the burn marks are on the opposite corner of the board.
I'm really confused by this one. I cannot find anything that could have caused this.
Maybe something fell into the unit and caused a short? Really do not know.
Have some new caps coming and I will replace those orange ones just in case.
(maybe the brown ones too)
Mark
Hi Mark,
I did see this listing on ebay.
I did notice in one image from the listing, what looks as a bad tantalum capacitor
The top one in the lower left corner, looks as it has failed and been hot.
Regards,
Askild
On Fri, Feb 24, 2023 at 2:30 AM Blue Smoke Lee < pedlowl@...> wrote:
It¡¯s not that tantalum¡¯s are unreliable, to the contrary, they are very reliable and have long service lives.? Instead, it¡¯s all about HOW they fail when they do (eventually) fail.? Most aluminum electrolytics fail by having an increasing esr
value over time up to the ultimate end of life state of an open circuit.
A tantalum capacitor¡¯s failure mode is most often as a short circuit.? If the tantalum cap is in a circuit capable of delivering a reasonable current, that results in fire.? I¡¯ve got a field returned product in front of me right now with exactly that situation.?
It¡¯s a game of probabilities and that¡¯s why some manufacturers have banned them.?
In the older HP gear I restore and collect for a hobby, I see lots of the egg and epoxy axial tantalums go poof. It¡¯s one reason I can get an expensive instrument so cheaply.? In those cases, the current is limited so there is no roaring bonfire, but the
tan egg does let out the blue smoke even though the supply voltage and ripple is entirely within spec. I just repaired a HP-8663 that had a tantalum filter cap in a 15 volt internal module supply bus go poof.?
? "Blue Smoke Lee" <pedlowl@...> writes:
Tantalum caps are notorious for going into ¡°kingsford mode¡±, where they fail exothermically.? Your photo shows characteristics of a tantalum cap failure and it¡¯s one of the
more mild failures I¡¯ve seen.? I recall a case where the tiny tantalum cap burned through multiple Fiberglas layers and torched the opposite side of the board. Many companies
have rules prohibiting the use of tantalum caps in product designs for that same reason.
Tantalums should be very reliable if treated with respect. Specifically,
follow Dave's advice and derate it sufficiently.
I found the following two posts very helpful:
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/g/HP-Agilent-Keysight-equipment/message/122066
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/g/HP-Agilent-Keysight-equipment/message/97724
Matt
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