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  #1  
Old 01-11-2019, 08:54 PM
Ed_Wischmeyer's Avatar
Ed_Wischmeyer Ed_Wischmeyer is offline
 
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Location: Savannah, GA
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Default Do it yourself audio panel repair (?)

So my otherwise wonderful PS Engineering 5000EX died this afternoon, and since it's out of production, support is pricey -- $200 plus time and materials. I've purchased a plug-compatible Garmin intercom, but the question is, what do I do with the old one? Sell it? Try to fix it? Use it as a boat anchor for a very small boat?

The symptoms observed this afternoon were:
1. Moderate frequency buzzing in pilots right earphone if the headphones weren't on tight. (Lightspeed Sierra headset) (That symptom might be a red herring);
2. Passenger microphone had difficulty breaking squelch;
3. Passenger microphone would not break squelch;
4. Unit died completely -- no intercom, passenger side PTT inop, no lights on the front of the unit.

Any thoughts? Suggestions? Offer$?

Thanks!

Ed
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  #2  
Old 01-12-2019, 05:07 AM
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snopercod snopercod is offline
 
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You might check the internal power supply. That would be pretty easy, I think.
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  #3  
Old 01-12-2019, 07:52 AM
FinnFlyer FinnFlyer is offline
 
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Location: Bell, FL
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+1
Typically electrolytic capacitors degrade over time. Sometimes you'll see the telltale sign of the bottom (top) bulging out.
If a voltmeter won't do for troubleshooting and you don't have an oscilloscope to look at the power supply output, you can use the brute force approach of simply replacing the electrolytic capacitors. Trying that sure beats $200+.

Finn
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Old 01-12-2019, 08:13 AM
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DaleB DaleB is offline
 
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What FinnFlyer said. Electrolytic caps are cheap, and you can probably put in better parts than original. Also look for telltale color changes on the PC board, areas where the green is a little darker or lighter. This can indicate overheating components, often a voltage regulator or amplifier.
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  #5  
Old 01-12-2019, 08:25 AM
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n82rb n82rb is offline
 
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I haven't opened up that unit, but if it's less than about 15 years old I'm willing to bet is SMT. Not easily fix with out some special equipment on the bench.

Bob burns
Rv-4 n82rb
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  #6  
Old 01-12-2019, 08:39 AM
rapid_ascent rapid_ascent is offline
 
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I would tend to disagree about the SMT caps. The electrolytic caps can be replaced by hand pretty easily depending on your soldering skills.

I had a coworker that was collecting bad PC monitors at our work. He investigated and it turned out that most had bad caps. He bought some caps and told others how to fix them if they wanted.

Given that your failure was not a "hard" failure I would tend to agree with the assessment. When the caps dry out you lose their filtering capability. This results in the power supply having more AC noise on the DC supply. This is probably what you are hearing.
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  #7  
Old 01-12-2019, 08:51 AM
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Ed_Wischmeyer Ed_Wischmeyer is offline
 
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Thanks, all. This was a gradual degradation to a total failure -- now the lights won't even come on.

I've got the unit apart, emboldened by the knowledge that a replacement is on the way and that if I do irreversible damage to this unit while I'm screwing around with it, no big loss.

It has two surface mount boards with a zillion tiny components, a few custom ICs, and one umpty-gazillion pin connector running down the middle. One board is only half populated, indicating that that board was designed to work on other units as well.

There are no immediate signs of any distressed components -- no obvious discoloration, no holes where the smoke escaped etc. I'll get out the magnifiers and look again, but at this point, no smoking guns... or anything else smoking.

I'll get any number of hundred dollar hamburgers out of this one and won't even have to drive to the airport.
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RV-8 (steam gauges), RV-9A at KSAV (Savannah, GA; dual experimental touch screens with autopilot, IFR GPS)
Previously RV-4, RV-8A, AirCam, Cessna 175
ATP CFII PhD, so I have no excuses when I screw up
2019 dues slightly overpaid
Retired - "They used to pay me to be good, now I'm good for nothing."

Last edited by Ed_Wischmeyer : 01-12-2019 at 09:38 AM.
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  #8  
Old 01-12-2019, 08:59 AM
FinnFlyer FinnFlyer is offline
 
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Start at the +12 volt input and see if you can track the traces from there.
I do agree that trying to repair surface mounted components is a lot harder than old stuff. I actually pretty much stopped doing electronics repairs around the time they became prevalent. (Yes, I'm old)

Finn
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  #9  
Old 01-12-2019, 09:39 AM
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DaleB DaleB is offline
 
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I have found that a 10x lighted bench magnifier, a pair of curved sharp pointed tweezers, and a decent soldering station with very fine tips for the iron make SMT work not that big of a deal. Doesn't take anything really fancy, my Weller WES50 was under $100. I've hand soldered a number of fairly dense prototypes. I use solder paste and a heat gun when able, but using the iron is not that tough.

And speaking of the heat gun... Ed, another thing that will cause intermittent problems degrading to total failures, as you have experienced, is bad reflow solder joints. They can be almost impossible to spot. SMT boards like that get a solder/flux paste applied with a mask (similar to silkscreening), then the components are placed by robot. After that they go through an oven that melts the solder and everything gets soldered at once. Problem is, sometimes that reflow process is not perfect. You can get bad solder joints that don't show up for weeks, months or even years. Trust me, I've had it happen on my own products. If you have nothing left to lose, a heat gun or toaster oven can be used to gradually heat the board until the solder flows again. That may fix it. Gotta be careful with a heat gun, though -- it's possible to melt the solder and blow the components out of place.
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  #10  
Old 01-12-2019, 09:56 AM
rv7charlie rv7charlie is offline
 
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Dale's not kidding about the toaster oven. One of the products quite a few of you guys have in your panel has its circuit board soldered in a literal toaster oven. You do need to know the correct temperature & timing, though.

Charlie
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