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Re: Tantalum Capacitors

 

Microdyne was strted by an engineer and a salesmmaman from Defense Eletronics, becuase they weren't interested in solid state designs. One of the owners ws still on the board when I worked there. (Hank Lin?) They used 1100 on doens of designs, and some had beeen in continuious service t BASA while I worked there. My first exposure was their various C-band receivers. They produced the best video of all nrands that United Video used in over 100 CATV headends. I ran the in house repair center,at out Delhi township system. The 1100LPR was the cheapest unit we used, but the best quality. The lowest was Scientific Atlanta, and Rockwe;;/Collins. Istead of using a couple transistors or an IC to shift the DC offset of the video, they used a lare electrolytic that often failed. This was in 1982-1986. It was obvious that they were a modifed fixed frequency military design. They used a tunable input filter, and a mechanically tuned LO fto convert directly from C band to 0 MHz. I once had 13 shipped to me from another site. They neded seven repaired. The biggest failure was the transistor in that 4GHzoscillator, with were NLA. They would make a natch of 15 for 41500 each. The 110 LPR was $800 and aile. Collins had over a six month turnaround. I often? had uits repaird and back in service within an eight hour shift. I had access to every Microdyne manual, until a few years ago, until the former Miccrodnye repiar tech retired and sold off everything. He was contracted by Microdybe to do out of warranty serviice for them.
I have an extremely rare Microdybe C band sigbnal generator that was built in ouse for final test on the production ine. I think there were aboubt a dozen built.
The 1200, 1400 and 700/1620 al used the same low phase noise snthesyser module we developed. I spent about six months working on them, and upting the design and test process afer some uncased disk capaciors became NLA.?

Enugh rambling, on here.You can contact me by email if you want to continue thee discussion, so we don't bore other memers..

On Thu, Nov 28, 2024 at 6:55?AM Michael A. Terrell via <terrell.michael.a=[email protected]> wrote:

Weren't some of these only identified by the lead length of the positive side?

On Thu, Nov 28, 2024 at 6:05?AM Dave_G0WBX via <g8kbvdave=[email protected]> wrote:

Re:-

"Some tantalum capacitors needed a small resistor of a few ohms in series with the supply voltage to limit the dV/dt and inrush current as well."


Oh Yes indeed!? In truth, I suspect all "Tantalum" cap's have a surge current limit, that if exceeded will do them damage...

In the immediate past full time day job, I ended up having to replace several SMD type 68uF/50V parts (similar to these: ) that were used to decouple an incoming +20V high current supply, that itself was switched by a relay contact.? The PSU was rated at several 100W on that rail.

I quite soon (with a bit of online research) discovered they don't tolerate surge currents that well (if at all) but could not convince our product designers of that fact, even by sending them extracts, and complete data sheets from the manufacturer they used.

(The relay contact would also pit and fail after some time too.? Another "schoolboy mistake" they made, but again not interested in mitigating.? In later versions of that product, the PSU was commanded On/Off, rather than use a relay on it's output.? It was a custom multi-rail type by then, so I guess someone else with more clout than a wholly owned subsidiary doing support and repairs could wield.)

I (like others on this list) fitted electrolytic parts instead, if they fitted inside the module (and other parts of the module, such as nearby components or the board itself were not badly damaged.)? Else, they were fitted to the outside of the case.

The data sheet from maker used (Vishay I think in that case, but I cannot be sure of that) also indicated that the larger SMD Tantalum parts, needed "annealing" after soldering to a board, to reduce/remove internal stresses built up during the SMD soldering phase, that could cause premature failure.? Something else our "engineering" types did not want to know, and/or failed to acknowledge.

In a past (much earlier) work life, I had first hand experience while working for Tek in the UK, of the great "Tantalum fitted the wrong way round issue" in such instruments as the venerable Tek 465 'scope.? Oddly, they'd often last long enough to just get past the warranty period!? A quiet failure too, the 'scope would just suddenly shutdown, or just fail to power up when needed.? No uncontrolled "Fire and Brimstone" events.? Plus, the bad ones were difficult to spot, unless they sported a small silver "blob" somewhere on their body, but they we found would often fall off during de-casing the instrument.

The quickest way to find them was brutal.? Pull the collapsed PSU rail current limit sense transistor and wait....? Sometimes it would take another hour, other times a few seconds.? I used to put the s'cope on a turntable standing on it's rear with the cover off, so it could be rotated when the smoke came, to find the culprit.? (With the intensity turned down, and fully de-focused, in case when a cap' failed, that could result in a static high intensity beam.)

Power down, remove, clean up, install new part, taking great care to fit the right way round!? And re-test.? One instrument went through that three times that I know off.? Most, were just single event failures.

Of course, a full performance / calibration check was performed before returning the unit to the customer.

In Tek's defence, those parts were the multi coloured bead types.? Some makes were not exactly obvious which lead was the +ve from the colours and layout of the markings used..

I still wonder if any survived and "re-polarised" themselves (If Tant' cap's can even do that) and have had a long working life.? I have a 465 and 485, both riddled with the things, both still work well.

Regards to All.

Dave 'KBV
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