Can a faulty Electronic device interrupt another good device?

Thread Starter

mohammod

Joined Aug 10, 2022
2
I am using a VHF RT, it's power supply requirement is 27 V DC. When this RT becomes unserviceable and I run RT and HUD(Head Up Display of an aircraft), HUD becomes blurred. The power source is the same for both these devices. Though there is no physical connection between these two devices but why it's happening?

(Sorry for my bad English)
 

ci139

Joined Jul 11, 2016
1,867
When the RT inserts some waveform to the supply , then it may be pass through the HUD supply filter (if any such is implemented)

This however requires relatively high impedance 27V supply --OR-- relatively lengthy parallel running power lines for both mentioned devices
 

MisterBill2

Joined Jan 23, 2018
12,697
Short answer is YES, one device on a power circuit, in some fault modes, can easily interfere with other devices on that same power feed. Solving that problem may not be at all easy.
 
Are you sure it's not a power supply issue? If one is working, but the other causes both to not work correctly I would look at power connections first. Make sure you still have 27V at your connectors with both connected and ground is the same as battery or chassis ground.
 

petermif

Joined Dec 8, 2016
3
This sounds like a power supply issue ( good chassis grounding, filtering, noise injection, loading etc) or possibly the RT is faulty and generating noise / spurious oscillation on the supply lines which disrupts the HUD. Your comment about the RT becoming unserviceable is a bit ambiguous so perhaps a bit more detail here would help.
 

MisterBill2

Joined Jan 23, 2018
12,697
First of all, the TS stated Power SOURCE, not a power supply. The source being 27 volts points toward it being avionics equipment. A "VHF RT" I am guessing is what I would calla VHF transceiver, which means both transmitter and receiver. "unservicable" could mean stuck in transmit for some reason. That could be a big load on the power source, or be transmitting interference causing the symptom.. And in aircraft the stuff is often connected via a digital bus of some sort.
 
My thought was maybe there is a weak connection that will cause both to draw the incoming power down far enough to cause problems. Power source and supply means nothing in the context of my line of thinking. A weak connection is a weak connection.
 

MisterBill2

Joined Jan 23, 2018
12,697
Certainly a weak connection can lead to other problems and interaction between unrelated systems. If the radio is drawing excess current that is one problem, if it is putting noise out into the power connection that can be another set of symptoms, and if it is stuck in the transmit mode that can be additional problems. So switch off the radio and see if that stops the interference.
 
I saw your last post and got a bit cranky I guess. In post #1 the TS states this is in a aircraft. Post #4 mentions a 28V auxiliary power supply unit. Personally I was thinking a 24V automotive type system as I don't have experience with aircraft.
Other than that everyone has had valid thoughts and suggestions based on what little information has been given so far.
 

MisterBill2

Joined Jan 23, 2018
12,697
If for any reason the RT (two way radio) becomes "unserviceable" then the aircraft should remain on the ground. Failing avionics is a good start towards a fire while aloft, leading to bad situations, at best. So the first requirement is to do what is required to make the "RT unit" serviceable.
 

Ya’akov

Joined Jan 27, 2019
6,264
To answer the question posed in the subject: if two devices share a power supply they have a connection that will allow one of them to possibly affect the behavior of the other.

If this will be the case depends on things like the capacity of the supply relative the the current requirements of the devices and the design of the devices involved.

So yes, two devices sharing a power supply can interact because of that shared connection even though they are not otherwise connected.
 
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