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Posted: 6/19/2017 1:07:08 AM EDT
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Hey everyone.
I picked up a pvs-14 in a trade. The image is clear, but considerably dimmer than my Pvs-7D's. In addition the manual gain does not appear to work. Opening the unit up, everything looks ok. No connections are cut or appear damaged, but I haven't done any electronic testing on them. The unit is fully functional, I'm just disappointed in how dark the picture is. Is the tube going bad or damaged? Anything I can do to isolate the issue? Also, I've been trying to ID the tube. It's unmarked except for the ser # and KM272864-8 (which I believe is the power supply). Thanks in advance for any help! Chris |
| The image noise appears fairly low. The picture is just considerably darker than my 7D. It is especially pronounced when indoors or shadows using only ambiant light. When using the IR illuminator, the image is greatly improved. It feels as though the tube is not magnifying the light enough, or as you mentioned, the gain is stuck in the low position. |
| I bought a "brand new" single battery compartment to upgrade an old dual battery PVS-14. I had the exact same problem. The issue was in the new battery housing. A second replacement housing fixed the problem. I think a lot of the "brand new" surplus battery housings are junk. I never investigated the housing. I just returned it from whence it came. It could be something as simple as a miswired gain potentiometer. |
| Can you measure what resistance values the pot gives you? Would narrow the possibilities down by one at least. The tube could be tested by itself by wiring a pot to the pigtail, or a resistor. I don't remember the values, someone else need to give you those sorry. |
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The tube needs just a 3V source, 2xAA or 1 CR123, or a variable power supply you can tune to 3V. The pigtail doesn't need anything if just checking for a second, but it will be on very high gain without a resistor in between. That though would probably tell you already a lot of the problem if the gain jumps sky high (too high!) for the quick test.
But, please wait for others to tell you the actual resistor values so I don't tell you anything that messes your tube up! |
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So I hooked up a multimeter to the board. The gain potentiometer is showing 0-180 (depending on position) ohms, which I believe is about right (200 ohm is spec I believe). Im concluding that the potentiometer itself is working properly. I also measured the DCV power output. The power supply is putting out 2.97v constant, regardless of where the gain potentiometer is set. Is this correct? I'm assuming that the power variable is in the tube as the pigtail is attached to it?
I'll try to test the tube later this evening. |
| if the housing part is all ok then you could try to adjust the gain on the pigtail board or look at the mcp voltage as the screw for that looks exposed and might have been fiddled with(top of tube ). just make a note of each adjustment so you can put it back to the positions if you need to |
| A little addition to what johnelot said, and I may be reading his post wrong as I am not a native English speaker, but you can't actually look or measure the MCP voltage, it's internal, but both the pigtail and the exposed potentiometer on top of the tube adjust the MCP voltage which then dictates max gain. |
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Quoted:
if the housing part is all ok then you could try to adjust the gain on the pigtail board or look at the mcp voltage as the screw for that looks exposed and might have been fiddled with(top of tube ). just make a note of each adjustment so you can put it back to the positions if you need to 
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| Ok, so I did some testing on the tube. All electrical connections appear to be working as expected. I used a couple of alligator clips to apply power from he power source to the tube without the pigtail connected. Viola! Everything worked properly. Gain was high and the adjustable gain functioned normally. I reassembled the unit and tested again holding the device shut. Again, everything was bright and working as it should. I put the four screws back in and tested it again, and Boom, back to square 1. Low gain, adjustable gain not working. I removed the screws and sure enough, the unit started working normally again. I found that depending on how tight the cover was affected how the unit worked. At this point I have no idea why. I do feel however, that this latest discovery eliminates the tube as being defective. The tube appears to perform normally under the right circumstances. I now need to find what is causing the variance when the unit is tightly sealed (screwed together) vs. being loosely held together. |
| I would start with where the forked connectors meet the contact pads on the tube. With no bateries smear a light coat of grease on the pads amd tighten the screws. Open the unit back up and look to see if the forked connectors didnt loose contact with the pad area |
| So I've made some progress on troubleshooting. Was able to borrow a PVS 14 from a friend and connected his battery housing to my tube. When doing so, the NVG worked fine. So now I know the problem exists in the battery housing. Moving on from there, I attached power leads from the battery housing to the power contact points on the tube. Again, the unit works fine in this configuration. Only when the unit is assembled and the screws torqued down does the problem resurface. If i put the unit together loosely, it works fine. As the screws are torqued down, the gain goes dark and the gain adjustment ceases to function. My suspicion at this point is that something is getting pinched/bent when the unit is torqued together. Does anyone out there have any last troubleshooting ideas, or should I go ahead and buy a new a battery housing? |
| you could put the alligator clips on the power supply contacts and power just the battery compartment up -keep an eye on the voltage , then poke about and press here and there to see if the pcb is cracked or if there is a dry joint on it somewhere , like i said , it seems to be the latest type housing with an earlier gain switch so if that has been swapped then maybe a joint is loose etc. |
| My thinking exactly. I did just what you said. Problem is, the results baffled me even more. Keeping the board apart from the Tube, I applied power and everything worked normally as I expected. I then began applying pressure to various locations on the board hoping to find an area where I could reproduce the problem. No matter how much pressure I applied to the board, I was unable to reproduce the issue. I then had the though that maybe the board was getting shorted some how. So I covered the board using electrical take and reassembled. The tape made no difference. More data points, but I'm still baffled by this one. |
| so you get the right volts on the contacts testing the battery compartment that way but it could be the pigtail connection that is at fault as it seems the gain is lost when you tighten the screws so - did you try the other persons tube or another tube in the housing ? - just in case its a bad connection internaly on your tube and when it has any pressure on the side of the tube it goes bad ? or hold the tube on the battery conpartment (pigtail plugged in )as if it is in the housing and press gently here and there - be very carefull and not too rough though (in a dark room ) sorry a lot of ideas there |
| Yeah. I tried the battery housing from a known good PVS 14 and it worked fine. Also, if I assemble the unit without the gain connected, the tube is at full brightness. To me, that eliminates the tube as the culprit. I've ordered a new battery housing. We'll see if that fixes it. I'll report back once I get it wired up |
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So just to close out this thread...
I got the new battery housing. Wired it up and everything now works as it should. Gain works properly and Tube is nice and bright. I never really was able to determine what the actual defective component was. All I know for sure is that it was something within the batter housing. Luckily, I was able to find a user battery housing on the EE for a great price. (Thanks ARMCOM) Thanks again to everyone on this thread who helped me to get to the bottom of this. Thanks to you all I have a fully functional PVS-14 again! |
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Quoted:
So just to close out this thread... I got the new battery housing. Wired it up and everything now works as it should. Gain works properly and Tube is nice and bright. I never really was able to determine what the actual defective component was. All I know for sure is that it was something within the batter housing. Luckily, I was able to find a user battery housing on the EE for a great price. (Thanks ARMCOM) Thanks again to everyone on this thread who helped me to get to the bottom of this. Thanks to you all I have a fully functional PVS-14 again! you should donate it to me, for science and learning and stuff. 
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