Raytheon JPS SNV-12 Preventative Maintenance Tip

[Wile E. Coyote]

After battling some odd audio problems with one of our older SNV-12 voters, I managed to troubleshoot the problem to the Power Supply Module. When I called Raytheon tech support, they identified two capacitors in the -12V circuit that have been known to go bad with age.

The next time you service a JPS SNV-12 voter that is 10 or more years old, you may want to replace C11 and C12 on the Power Supply Module. They are both 100uf, 25V caps. Because they are co-located near a number of heat sinks, I used high-temp caps (Mouser # 647-UVZ1E101MEH).

So far I have replaced the caps in eight older voters and ALL of the removed caps tested poor. I hope this will help some of you (and your customers) out.

WEC

[Bill_G]

Right on. thanks!

[Lake Effect]

What kind of odd audio problems did you see? I ask because a customer reports hearing some kind of "echo" when a certain site is voted.

L.E.

[Wile E. Coyote]

We observed intermittent staticy/hissy TX audio and tones from the console and all sites. Eventually the LLGT was delayed or missing all together. Apparently the -12V supply is key to some of the audio switching circuitry in the rest of the system. As the caps go bad, the -12 rail will begin to sag.

The -12V LED on the face of the PSU is not on a comparator, it's just an led with a resistor on the -12V rail. If the voltage begins to sag, you might notice the LED getting a little dim, but it will not go out (unless things have really gotten bad)!

@ Lake Effect - As for the echo, check to make sure all of the settings in your SVM are set correctly. You can verify this by swapping the SVM for your problem site with another known good one. See if the echo follows the site or the SVM.

[Pat]

Is a dim -12V LED indicative of the capacitors failing? The -12V LED on our SNV-12 is noticeably dimmer than the +12V LED. Our SNV-12 is only about 5 years old, however.

Pat

[Wile E. Coyote]

Pat,

The tech at Raytheon did say that the LED would look dimmer if the voltage started to sag. I have replaced caps in 4 more voters since my last post - ALL of them tested marginal (around 20% rated value) or poor (>20% rated value).

I had one 100 uF cap read 5 uF on the tester. It's standard practice to replace these caps in our shop now. If you have a dim -12V LED, then I would definately think about replacing the caps. besides, it's not like the parts are expensive or hard to access.

Good luck with your voter!
-WEC

P.S. - If this solves your problem, let us know!