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 SM migration help

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steve_b



Posts : 5
Join date : 2010-10-16

PostSubject: SM migration help   Wed Oct 20, 2010 4:26 am

http://i28.servimg.com/u/f28/15/78/06/20/pa190111.jpg

This is from the same SX-99...T2 is on the way, thanks again, this is from the last IF transformer (T3)


most of the silver is missing from the one cap....seems larger value than the one that is somewhat intact..

I noticed a distinct HV clicking from the can while measuring voltages around it......looks like it vaporized most of the silver

measuring them is going to be worthless and looking for ideas where to start trying values to replace these with.......

this is the first time that I've ever dealt with this issue...what a pain


Thanks in advance for the help here

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k9uwa



Posts : 18
Join date : 2010-10-13

PostSubject: Re: SM migration help   Wed Oct 20, 2010 5:21 am

steve_b wrote:
http://i28.servimg.com/u/f28/15/78/06/20/pa190111.jpg

This is from the same SX-99...T2 is on the way, thanks again, this is from the last IF transformer (T3)

measuring them is going to be worthless and looking for ideas where to start trying values to replace these with.......


with the IF can laying on your bench you could attach your signal generator to it.. tack solder across that coil your guess of a capacitor. Then look at the other side of the IF can with a scope. Now sweep the signal generator and watch the scope for a peak of signal. Read Signal generator frequency were peak reading occurs. if low the reduce size of capacitor until frequency is where it is supposed to be... without moving the inductor adjustment on the IF can...

John k9uwa
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burnt fingers



Posts : 70
Join date : 2010-10-12
Location : New Hampshire

PostSubject: Re: SM migration help   Wed Oct 20, 2010 6:30 am

As was mentioned in an earlier thread for a SX-99 the capacitor is usually between 80-120pf and is not critical as long as the slug tunes thru a complete peak. A 120pf seems to be the most common value Ive found and this can easily be done by trial and error with the replacement cap external across the terminals.

Carl
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steve_b



Posts : 5
Join date : 2010-10-16

PostSubject: Thanks guys....   Wed Oct 20, 2010 7:09 am

I'm on it...I really appreciate all the help I've gotten on here...

The XYL has fallen in love with this old monster...I have a feeling that it will be replacing
the DX-302 she uses all the time...

Rolling Eyes


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OZ132HOME



Posts : 9
Join date : 2010-10-13

PostSubject: Re: SM migration help   Wed Oct 20, 2010 9:10 am

We need to start a March of Dimes or something to support a cure for this dreaded disease (SMD)... Rolling Eyes Rolling Eyes Rolling Eyes Rolling Eyes Rolling Eyes
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k9uwa



Posts : 18
Join date : 2010-10-13

PostSubject: Re: SM migration help   Wed Oct 20, 2010 9:57 am

OZ132HOME wrote:
We need to start a March of Dimes or something to support a cure for this dreaded disease (SMD)... Rolling Eyes Rolling Eyes Rolling Eyes Rolling Eyes Rolling Eyes

Don't forget guys This HORRIBLE Disease is not just inside IF Cans. It can and does rear its UGLY HEAD in Mica Caps as well. Had it recently happen in a Zenith 10s153 type chassis.
Same ugly type sound. Snap Crackle and Pop ... thought I was about to have my breakfast of Champions.

John k9uwa
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radiotechnician



Posts : 35
Join date : 2010-10-12

PostSubject: Re: SM migration help   Wed Oct 20, 2010 11:31 am

Finding early stages of SM was done with signal tracers like the Heathkit T-3.

The high gain amplifier probe was biased with about 90 volts through a high resistance
in the 'noise test' , Power-down chassis then could be probed to find noisy capacitors,resistors, or even suspect insulation failures (whiskers and carbon tracks).

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Tim Tress



Posts : 12
Join date : 2010-10-17

PostSubject: Re: SM migration help   Thu Oct 21, 2010 6:14 pm

On first glance, my newly-found RCA Radiomarine AR-8516 has the dreaded silver-migration-prone IF transformers, but a study of the schematic shows that they all have outboard mica capacitors. Maybe the problems with those IF transformers were known early; apparently, it's from around 1957.

Tim KA3JRT
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