Re: Smokey 492A (very).


I cracked open my 492 service manual and I think I see your little fire-starter.

It is labeled "U301", but it is shown as a 0.1uF + 20 ohms: 0.1uF in series with 20 ohms, and that whole thing right across the AC line.

Tek PN 119-1168-00

Mfr PN given as 104MOGQC22, but Google doesn't help find it.

Since it's across the line, you should be able to replace it with an "X" type 0.1uF film cap, plus the 20 ohm resistor. I can't tell what size that resistor is (was), maybe you can guess from the size of the pile of ashes?


Good luck!



From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Stefan Trethan
Sent: Tuesday, August 16, 2011 10:54 AM
To: TekScopes@...
Subject: Re: [TekScopes] Smokey 492A (very).



You could certainly make money with that, every few years we hear about "smellyvision" so why not email?

I've only seen mylar (or other plastic foil) fail across the power line, most X capacitors seem to be plastic.


On Tue, Aug 16, 2011 at 5:24 PM, J <rpoz28cam@...> wrote:


LOL @ emailing the smell.  Good one!  I tried that one time with an old girl friend when she was making cookies..(grin),  really hard to accomplish!

Were those ceramic disc caps placed across those lines? .. or mylars?





From: Stefan Trethan <stefan_trethan@...>
To: TekScopes@...
Sent: Tuesday, August 16, 2011 10:17 AM
Subject: Re: [TekScopes] Smokey 492A (very).



I forgot to say if it was a capacitor across the power lines then no, it is not needed for operation. It is only there to meet EMI requirements and you can just leave it out if you have no spare on hand.


On Tue, Aug 16, 2011 at 5:14 PM, Stefan Trethan <stefan_trethan@...> wrote:

I have had foil capacitors fail in the same manner also with copious amounts of smoke.
In all cases the smoke signal was given a short while after the equipment was powered, not instantly.
That would be my best bet, since them caps are more common than MOVs.

If you could email the smell, I could probably tell you what it is.



On Tue, Aug 16, 2011 at 4:54 PM, J <rpoz28cam@...> wrote:


Can you say MOV?  Metal Oxide Varistor - used for line transients and also could be part of the EMI / RFI componentry.

There could be two of them too!  Strapped from mains hot to ground and from mains hot to mains neutral. 


They do have a tendency to break down at times after 20 years or so of existence.

Hope this might help.





From: Don <vk3yv@...>
To: TekScopes@...
Sent: Tuesday, August 16, 2011 7:31 AM
Subject: [TekScopes] Smokey 492A (very).



Hi I have a problem with my 492, on switching it on tonight all came up OK. I left the room to get a patch lead and on returning 30 seconds later the room was full of smoke, the display was still working ok except the readout was jittery again ( been fixed before) but the smoke was pouring out from the back, I pulled the mains plug and proceeded to remove the power supply thinking the worst but as it appeared to be still working I was somewhat puzzled. Got the P/S off and started looking,feeling,smelling and nothing was hot. On further examination it appears that there was something wired diectly across the IEC socket that was rather smelly and black and burned beyond recognition. It appears to have been strapped to the line filter with some sort of tape. Maybee a cap? but I have misplaced my DVD for the 492 so I am wondering if someone can tell me what this black blob is and whether it is vital to the operation, I wont know until I find out what it is.

Many thanks,
Don VK3YV .....








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