***BANG!***

---------------------------

With tons of smoke and bits flying a well.

On two occasions, I have been in the same room at the time and had it filled with acrid smoke.

Wima X2 types both times, but others are really no better.

Hot environments make it happen sooner, IME.

X2 caps are "double wound" effectively two is series to avoid internal corona that occurs across microscopic internal air gaps.

Y caps are often ceramic or wound "in vacuo" to avoids the issue.

.... Phil

Let me clarify that these RCA line caps were film caps and did not go off l ike a gunshot like shorted electros do. I would say the sound they made wa s over several seconds or even minutes and would likely have sounded more l ike a piece of metal shoved into a bench grinder.

I mentioned a story I might relate earlier in the thread, and here it is: I was doing a house call back in the early 70s with my dad. It was a low en d metal cabinet Sylvania hybrid (tube/transistor) that had a tripped breake r.

The breaker was old and creaky and wouldn't reset, so my dad gave it a coup le of whacks with the back the nutdriver he used to remove the back. The breaker went in and the TV lit up, but it was dark, shrunk on the sides, ri ppling, and making a loud hum. Just as my dad was explaining to the custom er that it would need a filter (multi segment chassis mounted can electro) we heard a loud hiss for a couple of seconds and before we could pull the c ord out, the can electro blew the aluminum cylinder off with the sound of a gunshot. The room was immediately filled with an acrid gray smoke and the people bailed out of the house in a hurry.

The can let go with such force that it actually left a clean circle imprint ed upwards in the metal cabinet. Given that the filter housing was lightwe ight aluminum and given how far it indented the heavy steel cabinet, it mus t have been launched with impressive speed.

The customer did not want the TV even though it only needed a filter and br eaker, and we brought them a new Zenith the next day.

This mains inlet module requires some special service tool to be able to withdraw it from rear. THEN you get full, unobstructed access to the capacitor in question. Unfortunately, I don't possess that tool.

Well, quite. So I'm wondering if those caps have a different convention to others in their voltage ratings. Perhaps in the case of x-caps, that "250V" essentially means:

"This cap is designed to cope with European voltage levels and is safe to use across UK mains of the range 220-250V and brief transients vastly in excess of this limit can also be accommodated."

Just my 2p worth.....

A special tool? if it is a snap in type, all you need are a couple screwdri vers. One to depress the tabs, an another to push against the body. Work on e end then the other until it pops free. I've removed hundreds of them, tha t way from scrapped computer terminals.

erefore, leaving a part out of a design is "hack".

Damn, where have you been hiding for half a century? I recently watched a s mall populated PCB snipped out of a hoover, ran perfectly afterwards. Years ago I removed nearly all of an entire PCB from a Sony TV, it worked afterw ards. A big complex psu pcb. A huge proportion of e-stuff has bits in it do esn't need. There's an assortment of reasons why. I don't see how you could design stuff without knowing that.

NT

That approach is the right one for mil spec kit repairs. It is inappropriate for domestic kit.

NT

y.

like a gunshot like shorted electros do. I would say the sound they made was over several seconds or even minutes and would likely have sounded more like a piece of metal shoved into a bench grinder.

I was doing a house call back in the early 70s with my dad. It was a low end metal cabinet Sylvania hybrid (tube/transistor) that had a tripped brea ker.

uple of whacks with the back the nutdriver he used to remove the back. Th e breaker went in and the TV lit up, but it was dark, shrunk on the sides, rippling, and making a loud hum. Just as my dad was explaining to the cust omer that it would need a filter (multi segment chassis mounted can electro ) we heard a loud hiss for a couple of seconds and before we could pull the cord out, the can electro blew the aluminum cylinder off with the sound of a gunshot. The room was immediately filled with an acrid gray smoke and t he people bailed out of the house in a hurry.

nted upwards in the metal cabinet. Given that the filter housing was light weight aluminum and given how far it indented the heavy steel cabinet, it m ust have been launched with impressive speed.

breaker, and we brought them a new Zenith the next day.

I'd appreciate it if I could email you briefly about this. Is there some wa y to?

NT

Oh, if they're x caps they're normally an ac rating.

NT

Like I said, you're a hack.

Yeah, I guess it would. Anyway, after hacking a hole in the bottom of the motherboard I was able to removed the cap in question from underneath and it looks far worse now I can see it properly. It definitely let go in a big way and now I'm pretty confident it was the source of the loud bang I heard. I've also carefully examined all the other sub-boards and the PCB underneath them and they're all fine. Shards of broken cap were scattered about the area of the explosion. Shame I had to butcher the board to get it out, but there was no other way open to me. I follow what you said about removing that j6 power connector but I just don't have the dexterity I'm afraid. So it was a case of Dremmel to the rescue! :-)

like I said you're childish.

That's your opinion. My opinion is that you're hack.

My opinion is you're Phil Alison and ICTFP.

-- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

Oh look, the hacks are circling the wagons.

heh. you said that already.

You seem to be floundering:

1. Are you sure that it was the HP VNA that blew a capacitor or something? When you removed the case, was it lit up?

1. Toxic smells tend to be cause by vaporized electrolye. That leaves a messy stain which should have been present. If you can't see the damage, perhaps playing bloodhound and smelling for the damage might help. Find a vinyl hose, cram it into your nose, and sniff around the VNA and the shop for the strongest smell. Unless you use an air freshener (nasal desensitize), you should be able to find the source many days after it went bang.

2. When you tested the electrolytics, did you use both an ESR meter and a capacitance meter? If the ESR meter doesn't show a problem, the capacitance meter might.

1. Do you have a UV LED flashlight? When tracking down bulging electrolytic problems on computah motherboards, I sometimes (not always) can seen the electrolyte residue using a UV flashlight.

2. Did you have the AC power switch set for 230VAC or 117VAC?

1. Check if the small is coming from a power strip. The MOV's sometimes go bang.

Argh, gotta run...

Thank you, Jeffrey. Not sure if you were able to read the thread right through, but it's been established that the blown cap was an X2 rated one fitted right across the incoming mains power line. It took a while to confirm this was the actual culprit as it was well buried under a load of spaghetti. When I finally got it out I was able to see it had literally exploded which accounts for the report I heard from 30' away. That cap has now been replaced and the device appears to be working fine again, although after 10 years of storage there's no doubt some re- aligning and whatnot to be done.

You can call me a hack as well if you like; I couldn't give a s*it TBH. I'm not very practical. I get the job done but it doesn't look as pretty as some genius like yourself would leave it. But do I care? Nope! Because the case goes back on and no one can see it anyway.