I heard the term "Mitcham Tagstrip" from a Mullard man, so it might have been a term used by one factory within the Philips organisation to make fun of another.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
You're using incompatible parts/compound
You didn't allow for shrinkage.
You didn't de-air it (i.e., pump it down in a small vacuum chamber)
Incompatible materials, poor layout
Something must have broken - maybe from the shrinkage, so this isn't really a different item.
Using incompatible connectors.
But, admittedly, good, resilient potting compound is horrendously expensive - maybe you should try just "conformal coating".
Good Luck! Rich
It only seems like a long time in retrospect. While it's actually happening, it's like, "Oh, Sh-BAM!"
Thanks, Rich
The US doesn't have any friends - only associates.
snipped-for-privacy@ukonline.invalid.invalid (Adrian Tuddenham) wrote in news:1h5p8r5.q33yvr160o0byN% snipped-for-privacy@ukonline.invalid.invalid:
I liked Tektronix's ceramic strips(now discontinued),I made many a test fixture with them.
-- Jim Yanik jyanik at kua.net
Its still running or on fire right now. I'd bet it is still running.
Defib is by its nature short term so it too will not have any creepage problems. The UL regs spend a lot of time on the clearances for continuous use because that is the vast majority of the cases.
-- -- kensmith@rahul.net forging knowledge
In article , Joerg wrote: [...]
This is what I thought until I tried it on a PCB or two. We tried about
10 samples and every time something bad happened. The number of units to get the process to work would have been more than we ever sold (5).Problems were like this:
The potting compount attacked the capacitors.
The potting compount shrank as it hardened and ripped parts loose.
The potting compount had holes in it.
The board because noisy after potting.
The board just doesn't work anymore.
The potting compound leaked into the connectors
-- -- kensmith@rahul.net forging knowledge
I had an ohshitosecond many years ago, when my motorbike hit some gravel. That's the time taken to fly perhaps 30 feet realising that the impact is gonna hurt! There's a space-time warp that goes with it, it seems like a minute, but it's probably 1/100 of that.
Barry Lennox
Hello Ken,
New ones, yes. Older ones could sit there waiting for a load to appear. Very dangerous. The TUEV guy made me do a long term test on it once and wanted to witness it. He scooted back from the unit on his office chair before I hit that big button...
Regards, Joerg
They were beautiful, you could even drop the instrument into water and then switch on again after allowing a few minutes for it to drain; some Eddystone radios were designed to a similar spec.
Did you have a supply of high-silver-content solder so you didn't strip the plating?
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
Hello Ken,
Well, ok, on five boards it doesn't make any sense unless you hand-apply. But you had been saying potting requires quantities in the millions. With the hybrids we had no issues whatsoever, worked from day one. Key is to use a proven potting process and not trying to do it yourself. And no connectors, of course.
Our hybrids were laser trimmed to within 0.2dB and potting left them completely unfazed. They even let us pick colors other than the usual drab green.
We also potted 'poor man's hybrids' which used FR-4 instead of alumina. No problems either.
As an alternative there is conformal coating which is heavily used on stuff that goes into harsh environments such as oil exploration. I have seen a mainframe on a rig that accidentally got a heavy spritz from a fire hose. Our coffee mugs flew off the shelf and the chairs crashed into the back of the dog house. Water came running out from the bottom of the 19" enclosure but all the while the machine kept running.
Regards, Joerg
Not necessarily.
I had a similar motorcycle experience. A mechanical problem caused the bike to go into a horrible wobble at 70+ mph. I had at least a couple seconds where I hadn't crashed yet, but knew I would. Somewhere in there, my brain did something like this, in a couple milliseconds of parallel processing:
Normally at a time like this, I would think, "Oh, shit!", or "Oh, f*ck!", but this could very well be the last thought that passes through my brain, so -- "Oh, my goodness!!"
That really happened. As it turned out, I was extremely lucky. Landed flat on my back, wearing a leather jacket, and slid, and slid, until I eventually stopped and got up unhurt. Also all the cars behind me got stopped before running me over.
I often have an ohshitosecond late at night when trying to find my way home from the pub (bar for our US friends).
[etc]
If the temperature range isn't too great, what about using wax? It makes repair very easy.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
snipped-for-privacy@ukonline.invalid.invalid (Adrian Tuddenham) wrote in news:1h5ponv.1p3z4ve1awtqwwN% snipped-for-privacy@ukonline.invalid.invalid:
Yes,I worked for TEK for 21.5 years. Indy and Orlando Field Offices,both now extinct. To get the ceramic strips,all I had to do was walk over to the bench stock bins! 8-)
I still have about 3/4 lb roll of 3% silver solder.
-- Jim Yanik jyanik at kua.net
I dug out IEC60065.
The recommended track spacing ( d ) for voltage V is according to the following formula.
log(d) = 0.78*log(V/300)
That gives about 12.3mm for 7500V btw.
1kV > 2.5mmGraham
In article , Rich Grise wrote: [...]
So I found out. A sealed housing doesn't have this problem.
Yes I had but not enough for the batch that got made.
I sourced the process and yes it was de-aired before use by the people that did it.
Materials again.
I actually broke it apart to try to find out what happened. There were no obvious shrinkage effects.
Not, the connectors so much as the layout.
No, just put it in a housing and be done with it.
Where I work we still call conformal coating "circuit stop" even though "circuit coat" isn't sold anymore.
Conformal coating just makes trouble.
-- -- kensmith@rahul.net forging knowledge
In article , Adrian Tuddenham wrote: [...]
Better yet, just coat it with DC-5 or DC-111
-- -- kensmith@rahul.net forging knowledge
In article , Pooh Bear wrote: [...]
Its odd that there are logs in there.
d = exp(0.78*log(V/300))
d = (V/300)^0.78
At 1000V
d = (1000/300)^0.78
d = 2.55mm or just about 0.1 inches
So you should have said 2.6mm to be safe.
-- -- kensmith@rahul.net forging knowledge
My exact words about two minutes after the engine failed and about half a second after I took the left wing off with the bridge abutment.
(The boxes are ORANGE, btw.)
Jim
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