Garmin SL-40 Circuit Board Question

[Pilotjim77]

A friend accidentally crossed the positive and negative cables while installing a new battery on his airplane and turned on the avionics switch. He did not notice any smoke or burning smells, but after correcting the cable connections, the SL-40 and the GTX-327 don't work. After reading about Garmin's flat fee policy, I decided to open the units to have a look. The photo below is the SL-40 circuit board. My question is, is the substance under the 3 capacitors evidence of melting/burning, or does it appear normal (some kind of insulation)?

I tested the internal fuse in both the SL-40 and the 327 with a multimeter, and they both appear to be blown (no continuity).

Thanks for any help and input.

 

[rich]

It’s a type of glue to stabilize the capacitors from vibration.

 

[Pilotjim77]

It’s a type of glue to stabilize the capacitors from vibration.

That's good news, thank you.

Any thoughts on trying to replace the fuses on the circuit boards on each unit? I'm not confident to try it myself, but I thought maybe a local computer repair shop or radio shop. Doesn't make financial sense to send it to the manufacturer. The comm is $940 flat fee to repair, and the xpdr is almost $800. I could probably find used replacements for less.

 

[AZSteve053]

You could solder an automotive fuse across the factory soldered-in fuse and apply power, or just use clip leads to do it - and run a bench test to see if the power supply survived.
AND - There could be other issues hiding in the aircraft wiring & other components. Reverse voltage events are very unpredictable.

 

[rcarsey]

You've applied power to the devices directly.. or verified that the power pins in the tray have voltage .. and they still don't power on? I can't believe that they wouldn't have any reverse polarity protection.. thats like.. the cost of 1 diode. You can probably trace the path from the power pins to the first few components.. im sure the problem has to be very close to the power input pins..

 

[AZSteve053]

You've applied power to the devices directly.. or verified that the power pins in the tray have voltage .. and they still don't power on? I can't believe that they wouldn't have any reverse polarity protection.. thats like.. the cost of 1 diode. You can probably trace the path from the power pins to the first few components.. im sure the problem has to be very close to the power input pins..

A very standard avionics power supply design technique involves an internal fuse with a protection diode on the power supply side of the fuse which will be forward biased if reverse voltage is applied. The diode, in forward bias, draws enough current very quickly, to blow the internal fuse hopefully protecting internal parts from damage.

 

[Pdtofly]

A friend accidentally crossed the positive and negative cables while installing a new battery on his airplane and turned on the avionics switch. He did not notice any smoke or burning smells, but after correcting the cable connections, the SL-40 and the GTX-327 don't work. After reading about Garmin's flat fee policy, I decided to open the units to have a look. The photo below is the SL-40 circuit board. My question is, is the substance under the 3 capacitors evidence of melting/burning, or does it appear normal (some kind of insulation)?

I tested the internal fuse in both the SL-40 and the 327 with a multimeter, and they both appear to be blown (no continuity).

Thanks for any help and input.

If you can’t replace the fuse, pick up another unit. The GTX327 can be bought between $300 and $500 here.

As for the SL40, if you can’t replace the fuse, pick up another unit. They will cost around $800 to $1200. You are then better to send it in to Garmin for the flat rate repair and get it upgraded to the newest mod, and a warranty. The next best option is replace it with a new GTR200B. New radio, warranty, and new technology. The SL40 is 20 plus year old technology.

If you decide to upgrade, I know how to replace components on PCB, and would be interested in buying it from you, and take a chance at repairing it. If interested, email me at [email protected]

Brian

 

[Pilotjim77]

You could solder an automotive fuse across the factory soldered-in fuse and apply power, or just use clip leads to do it - and run a bench test to see if the power supply survived.
AND - There could be other issues hiding in the aircraft wiring & other components. Reverse voltage events are very unpredictable.

I thought about clipping leads and applying 12v power but was concerned about powering on the units without antennas.

 

[Pilotjim77]

You've applied power to the devices directly.. or verified that the power pins in the tray have voltage .. and they still don't power on? I can't believe that they wouldn't have any reverse polarity protection.. thats like.. the cost of 1 diode. You can probably trace the path from the power pins to the first few components.. im sure the problem has to be very close to the power input pins..

Yes, there is power to both tray connectors.

 

[AZSteve053]

I thought about clipping leads and applying 12v power but was concerned about powering on the units without antennas.

It's Ok to bench power either unit with no antenna connected, for the transponder do not select a transmit mode - standby will be Ok
For the SL40 - your fine as long as you do not try to transmit & of course you have no Push to talk sw so no problem
Be sure to not jumper around the internal fuse by just applying 12 volts to the power supply side - use an inline fuse like 7 amps for either to provide protection in case the unit is shorted out... protecting your bench supply (should be current limited) or test battery.
If units come-up... then solder in a replacement fuse and give them a test in the plane...

 

[Pilotjim77]

It's Ok to bench power either unit with no antenna connected, for the transponder do not select a transmit mode - standby will be Ok
For the SL40 - your fine as long as you do not try to transmit & of course you have no Push to talk sw so no problem
Be sure to not jumper around the internal fuse by just applying 12 volts to the power supply side - use an inline fuse like 7 amps for either to provide protection in case the unit is shorted out... protecting your bench supply (should be current limited) or test battery.
If units come-up... then solder in a replacement fuse and give them a test in the plane...

Outstanding, thanks for the info, Steve.