Audio Panel/Com Radio questions

[flyingcheesehead]

We're having an issue with a PS Engineering audio panel, and I'm curious what the potential causes for this type of failure are, and how the wiring works.

Basically, when I turned on the audio panel this morning, I noticed that the pwr/xmit light was red (indicating transmitting, green indicates "powered on"). We had another club member report that he had problems getting both intercom and com radio audio to work the other day.

I quickly switched it off, which on the PSE puts the left seat headset and PTT onto Com1. I asked Clearance Delivery to help me troubleshoot. I quickly turned the audio panel on, asked if she could hear me, and flipped it back off. She said all she could hear was airplane noise. I flipped it on again and had David (in the right seat) say something, and she heard him. So, I figured that the right-seat PTT was stuck. Physically, the button appeared to be fine, it traveled smoothly in and out with no apparent stickiness at all.

Next step, I pulled the PTT out of the yoke and looked for any sign that it was shorting out or anything like that, and found none. So, I clipped one of the leads, hoping that if the switch was bad that would at least allow full functionality except the right-seater talking to ATC. However, there was no change at all - The audio panel still showed a reddish light and appeared to be transmitting.

What can cause this type of failure? What kind of switch is a PTT anyway, would clipping a lead off it actually help or does there need to be some sort of continuity through it to *prevent* transmission? Does this issue sound like a short/open behind the audio panel, or could something else in the radio stack be causing it?

I should mention that I also noticed that I needed the radio up at full volume (which is not normal) to hear effectively, and while we didn't have any apparent communication issues with ATC, we may have had an issue talking to other airplanes at Lake Lawn this afternoon (I've asked them for clarification on what was actually transmitted/received by all parties in another thread). There were some quality issues communicating with one airplane there, and with Pete in his glider later on (though that may have been because he was on a handheld). Are the issues in this paragraph simply related to the way the PSE is hooked up to fail to com1? Or do we need to be looking elsewhere at the cause of all of the issues?

Thanks in advance for any information!

 

[CT Arrow]

Kent, you have two interesting issues that I would think are non-related. The PTT's are isolated in both circuits, Pilot & Co-pilot. Is the PTT light steady or flashing when the unit is turned on? Could be pinched or cut wire that finally shorted.

If it was me, I would remove the audio panel and bench test it to verfiy if the PTT issue is in the audio panel or in the wiring. The audio issue could also be checked at the same time. Which model audio panel is it?

NOTE: The audio panel gives priority to the pilot’s PTT. If the copilot it transmitting, and the pilot presses his PTT, the pilot’s microphone will be heard over the selected com transmitter.​

 

[ScottM]

BTW PTTs are generally SPST switches. You are just usually switching a voltage or a ground.

 

[Areeda]

Looks like PS Engineering has most installation manuals on line in pdf format at http://www.ps-engineering.com

Here's a couple of snapshots from the first one google found. I believe these are standard:

Yoke mounted PTT

Mike plug:

As you can see they both do the same thing, ie ground the PTT wire to the cable ground. So as was mentioned before it could be anywhere in the cable.

What happens if the copilot's mike is unplugged? It could be it wasn't plugged in properly or has a short.

Joe

 

[gismo]

Andy and Scott are correct in that the PTT is a SPST NO switch to ground on a wire that normally sits at +5 to 25 volts. It's clear from your description that either this wire on the copilot side is shorted to ground or the audio panel is malfunctioning. What you could do to discriminate between those two conditions is to remove the audio panel and measure from the appropriate pin on the tray to ground with an ohmmeter. If the resistance is low you'll need to track down the short in the wire and the most likely places are where it is flexed when the wheel is moved and inside the connector on the back of the tray. If the wire appears to be open, confirm you are on the right pin by shorting the switch wires together in the wheel looking for the meter to register low ohms. You can do all of this checking with the master off so there's no chance of shorting out something and causing further problems.

You can download the installation manual for your audio panel from the PSE website and it will have the tray pinnouts.

As to the low volume issue, I couldn't tell if this was with the audio panel on or off but IME the volume is reduced somewhat (not enough to require full radio volume to hear ATIS) when the panel is switched off (emergency bypass mode). If the low volume is mostly an issue when the panel is on, it's likely because of a deliberate attenuation that's inserted normally when a PTT is active so this problem may go away when you resolve the PTT problem.

One other note, some PSE units allow the pilot to transmit on one comm radio while the other pilot uses the second comm. If your intercom has this feature you might be able to activate that and turn off the second comm in order to use the intercom until you get the problem fixed. This function would also be useful in determining which PTT is stuck but you've already accomplished that.

 

[flyingcheesehead]

Kent, you have two interesting issues that I would think are non-related. The PTT's are isolated in both circuits, Pilot & Co-pilot. Is the PTT light steady or flashing when the unit is turned on?

It's "pink." It's not noticeably flashing, but since it wasn't dark red I think it may have been rapidly flashing between red and green.

Which model audio panel is it?

The 6000 IIRC. The one that is a slide-in replacement for the King I think. (It's been in the club longer than I have, so I'm not sure about that.)

What happens if the copilot's mike is unplugged? It could be it wasn't plugged in properly or has a short.

I don't think it would have been the mike plug, since this was reported by someone else first, and David and I switched seats as well, so it would have had to screw up the same way 3 times. However, it may be a wiring issue in the mic jack itself - I think our MO tried to test it the other day and didn't have a problem, but he didn't have anything plugged into the copilot side.

As to the low volume issue, I couldn't tell if this was with the audio panel on or off

Off.

but IME the volume is reduced somewhat (not enough to require full radio volume to hear ATIS) when the panel is switched off (emergency bypass mode).

Okay, that's probably it. Normally the radio volume is comfortable turned halfway up. I could hear it fine at full or nearly full volume. I guess we'll see what happens after avionics looks at the audio panel.

One other note, some PSE units allow the pilot to transmit on one comm radio while the other pilot uses the second comm. If your intercom has this feature you might be able to activate that and turn off the second comm in order to use the intercom until you get the problem fixed.

Would the intercom still work, though? It isolates the pilot and copilot in that mode (which we do have). I didn't think to see if that was dependent on the radio being on, though. We just had to not communicate much, and shout when we did. How on earth did people fly without intercoms and headsets?

 

[weirdjim]

If the PTT is a "built in" (i.e. drilled hole in the yoke) type then indeed it is an SPST normally open switch. If it is one of the portable "velcro around the yoke" type then you really have two versions. One version is pretty much the same thing as the built-in type with the mic line passing directly through the switch hardwired directly from the mic element in the headset to the mic jack on the panel.

The other type of portable PTT switch breaks both the mic line and the key line in the inactive (not pressed) mode. Typical of these is the Telex 300 series.

Just for reference, in a 12 volt system bringing the key line below 3 volts is considered "transmit". Anything over 3 volts is "receive". Double these voltages in a 24 volt ship. Caution for Microair radios and a couple of others reported ... they do not follow this RTCA standard. THey have to be brought below 0.7 volts (one diode drop) to go into the transmit mode.

Jim