ragedracer1977 Posted February 13, 2019 Report Share Posted February 13, 2019 Thoughts on how to troubleshoot this? Most of the time, the gauge works fine, but now and then (and becoming more frequent) the gauge just reads nothing. I've checked connections behind the panel but everything looks ok. Could the probe itself be failing? Trying to get a grasp on what might be wrong before I hand it over to the AP Quote Link to comment Share on other sites More sharing options...
carusoam Posted February 13, 2019 Report Share Posted February 13, 2019 This is probably the most simple gauge/sensor system in the panel... 1) find the sensor. Thermocouple. 2) follow the wires back to the panel... 3) Expect to find the sensor connected to some wires that are connected to the gauge... 4) clean each connection.... 5) the voltage is micro volts... any oxidation can cause a problem... 6) if the display/gauge is old, the microvolts may not be strong enough to power it any longer... Will probably work for the next 50 years... PP thoughts only, not a mechanic... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
zaitcev Posted February 13, 2019 Report Share Posted February 13, 2019 What is a Garwin gauge? Is it anything like this (mine is dead too): Quote Link to comment Share on other sites More sharing options...
ragedracer1977 Posted February 14, 2019 Author Report Share Posted February 14, 2019 3 hours ago, zaitcev said: What is a Garwin gauge? Is it anything like this (mine is dead too): Mine looks like this Quote Link to comment Share on other sites More sharing options...
carusoam Posted February 14, 2019 Report Share Posted February 14, 2019 Possibly the same six, in a different panel layout.... PP thoughts only, not a mechanic... -a- Quote Link to comment Share on other sites More sharing options...
Marauder Posted February 14, 2019 Report Share Posted February 14, 2019 What is a Garwin gauge? Is it anything like this (mine is dead too): If I recall correctly, the flat version are made by Rochester. Sent from my iPhone using Tapatalk Pro 1 Quote Link to comment Share on other sites More sharing options...
ragedracer1977 Posted February 15, 2019 Author Report Share Posted February 15, 2019 So. .. any suggestions? Quote Link to comment Share on other sites More sharing options...
Marauder Posted February 15, 2019 Report Share Posted February 15, 2019 So. .. any suggestions? Probe is high on the list for usual suspects for what you are seeing. If the connections look good, I would try to find a replacement probe and try that first. Pulling the gauge to send it out for repair is a bit of work. Sent from my iPad using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
Niko182 Posted February 15, 2019 Report Share Posted February 15, 2019 From what I remember, CHT isn't required as a Primary engine gauge so you can fly with it broken. Check the cable if its grounding or resisting somewhere. To be fair that box is probably a couple decades old. I'd at least look at a JPI 700 for EGT's and CHT's. if you want to get rid of all the engine gauges and so on JPI 900 or EI c30. Quote Link to comment Share on other sites More sharing options...
ragedracer1977 Posted February 15, 2019 Author Report Share Posted February 15, 2019 4 hours ago, Niko182 said: From what I remember, CHT isn't required as a Primary engine gauge so you can fly with it broken. Check the cable if its grounding or resisting somewhere. To be fair that box is probably a couple decades old. I'd at least look at a JPI 700 for EGT's and CHT's. if you want to get rid of all the engine gauges and so on JPI 900 or EI c30. It is required, unfortunately. Fortunately it's currently working, but something is going wrong as occasionally it isn't. I guess I need to trace the wire first, check connections on the back, and then the probe. See what I can see 1 Quote Link to comment Share on other sites More sharing options...
bradp Posted February 15, 2019 Report Share Posted February 15, 2019 First place is I’d check the number three bayonette if it’s working or not. Second if you’re sparky you can check the gauge with a power supply if you know the correct voltage across the thermocouple Third trace the ground . Quote Link to comment Share on other sites More sharing options...
zaitcev Posted February 17, 2019 Report Share Posted February 17, 2019 On 2/14/2019 at 6:57 PM, ragedracer1977 said: So. .. any suggestions? I'm just back from the airport. Mine turned out to be a poor connection at the probe. The terminal was annoying to reach and required a rare 3/16" nut driver. I didn't use any cleaning agents and I didn't have to solder. I updated the wire bundle clamp in hopes to reduce the vibration at the terminal connector. Very happy that I didn't need to source a replacement for Rochester cluster. It's harder to find than your Garwin. I took my Fluke with me, but the cold probe shows 0.000V and I didn't try the hot one, since my repair was successful. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted February 17, 2019 Report Share Posted February 17, 2019 Did someone say microvolts...? 1) millivolts... 10-3 those first three 000s after the decimal point... where that fluke meter is reading... Now for the hard part... 2) microvolts... 10-6 the next three 000s further to the right on the fluke’s screen! Glad you got the problem fixed without needing a more accurate tool... Sure makes the TC and meter a really impressive combination... Somebody (like Hank) Probably reminded me of this detail a few times before I got it into memory.... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
ragedracer1977 Posted February 17, 2019 Author Report Share Posted February 17, 2019 1 hour ago, zaitcev said: I'm just back from the airport. Mine turned out to be a poor connection at the probe. The terminal was annoying to reach and required a rare 3/16" nut driver. I didn't use any cleaning agents and I didn't have to solder. I updated the wire bundle clamp in hopes to reduce the vibration at the terminal connector. Very happy that I didn't need to source a replacement for Rochester cluster. It's harder to find than your Garwin. I took my Fluke with me, but the cold probe shows 0.000V and I didn't try the hot one, since my repair was successful. I think the first order of business is to replace the wiring. We poked around everything and didn't find any breaks or shorts. Traced both leads all the way back to the Garwin cluster. Everything looks ok (but old and the jacket is cracking in places) right up to the connections at the probe. It's a combination of plastic tubing, tie string, electrical tape, knife connector and spade connectors. It might be something that mess that causes the intermittent issues or it could be the probe or gauge itself. We'll try rewiring first. That's cheap and easy. Quote Link to comment Share on other sites More sharing options...
zaitcev Posted February 17, 2019 Report Share Posted February 17, 2019 1 hour ago, carusoam said: Did someone say microvolts...? 1) millivolts... 10-3 those first three 000s after the decimal point... where that fluke meter is reading... It's millivolts for common junctions http://www.ni.com/white-paper/4231/en/ 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted February 17, 2019 Report Share Posted February 17, 2019 Great charts, Zaitcev! I’m not understanding one detail though.... 1) TC type... got that... 2) temperature being measured... got that too... 3) millivolts being produced... check. 4) What is represented in the first column on the left? This just became a 3D challenge when I was expecting a 2D one... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
MikeOH Posted February 17, 2019 Report Share Posted February 17, 2019 (edited) That’s the starting temperature, you add the additional temp across the top to get the total temp. E.g., for 110 degrees you’d go down the first column to 100, then move across the cell under the 10 column...5.814 mV. Edited February 17, 2019 by MikeOH 1 Quote Link to comment Share on other sites More sharing options...
ragedracer1977 Posted February 22, 2019 Author Report Share Posted February 22, 2019 Solved! It ended up being a bad ground wire. Could not find any breaks in the insulation or any wire, but we tested a new wire and voila, it's back. So, ran new wires for both the ground and positive side. On another note, does anyone have a lead on a cheaper AN5546-1 probe than over $350?? My probe is now working fine, but the wires permanently installed to the probe are looking pretty ratty. If it was a regular bayonet probe for $40, I'd replace it, but I'm seeing $3-500 for the correct probe, and at that rate, I'll live with some less than pretty wires. Quote Link to comment Share on other sites More sharing options...
carusoam Posted February 23, 2019 Report Share Posted February 23, 2019 Brice can you tell what type of thermocouple it is? Typically they are K type. And if you stay with the same type, they are interchangeable... It is also possible to use a special splice kit if you want to replace the wires between the sensor and the gauge... usual +/- orientation still applies... the color of the insulation is a hint to what type of metal the wire is... mixing wire types will generate bad data... and win you a prize for being an errant CB... See what aircraft spruce has... PP thoughts, but ChE experience... not as good as a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
ragedracer1977 Posted February 23, 2019 Author Report Share Posted February 23, 2019 3 hours ago, carusoam said: Brice can you tell what type of thermocouple it is? Typically they are K type. And if you stay with the same type, they are interchangeable... It is also possible to use a special splice kit if you want to replace the wires between the sensor and the gauge... usual +/- orientation still applies... the color of the insulation is a hint to what type of metal the wire is... mixing wire types will generate bad data... and win you a prize for being an errant CB... See what aircraft spruce has... PP thoughts, but ChE experience... not as good as a mechanic... Best regards, -a- It's not a thermocouple, as it turns out. It's an RTD, which apparently increases the price by .5AMU. Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted February 23, 2019 Report Share Posted February 23, 2019 If you have the skills to disassemble it, you can just replace the RTD sensor inside for around $50.Tom Quote Link to comment Share on other sites More sharing options...
zaitcev Posted February 24, 2019 Report Share Posted February 24, 2019 (edited) On 2/22/2019 at 3:25 PM, ragedracer1977 said: Solved! It ended up being a bad ground wire. Could not find any breaks in the insulation or any wire, but we tested a new wire and voila, it's back. So, ran new wires for both the ground and positive side. Stupid question: where did that ground wire run, to and from? In my case, the return for the sensor was through a common ground strap to the engine block. Edited February 24, 2019 by zaitcev Quote Link to comment Share on other sites More sharing options...
ragedracer1977 Posted February 24, 2019 Author Report Share Posted February 24, 2019 1 hour ago, zaitcev said: Stupid question: where did that ground wire run, to and from? In my case, the return for the sensor was through a common ground strap to the engine block. All the way to the gauge cluster. Quote Link to comment Share on other sites More sharing options...
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