TV Fool  

Go Back   TV Fool > Over The Air Services > Special Topics > Antennas

Notices

Reply
 
Thread Tools
Old 18-Apr-2019, 1:40 PM   #1
dustyz
Junior Member
 
Join Date: Jan 2013
Location: KY
Posts: 29
Troubleshooting a dead pre-amp

I have a few pre-amps that have "died" over the years. Both still show voltage from the injectors, but neither show any boost in signal.

Is there a basic troubleshooting guide for the electronics in these things? Something that tends to go bad with electric spikes or lightning? I see no signs of burning or failure on the boards... mosfets seem fine.

Links or ideas? Maybe just a place to start? Thanks!
dustyz is offline   Reply With Quote
Old 18-Apr-2019, 9:39 PM   #2
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,549
Quote:
Originally Posted by dustyz View Post
I have a few pre-amps that have "died" over the years. Both still show voltage from the injectors, but neither show any boost in signal.

Is there a basic troubleshooting guide for the electronics in these things?
There is no basic troubleshooting guide for the electronics in preamps.
Even if you found a bad part, could you remove and replace a tiny surface mount component?

There are external tests you can make like measuring the current to the preamp, measuring the voltage at the preamp when it is connected, and measuring its gain. If it fails those tests, replace the preamp.
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html
rabbit73 is offline   Reply With Quote
Old 18-Apr-2019, 10:07 PM   #3
dustyz
Junior Member
 
Join Date: Jan 2013
Location: KY
Posts: 29
Gotcha. I've replaced plenty of parts on PC/videocard motherboards, so I could probably do ok with what I see on these. What could it hurt to try, ya know? I'd need to dust off the extra hands/magnifier, probably!

I was just curious if you typically started with the power, or the signal side... or if spikes caused X to go bad before Y. I'll see what I can dig up, and test what I can. Thanks.
dustyz is offline   Reply With Quote
Old 18-Apr-2019, 11:45 PM   #4
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,549
First power, then signal.

The spikes from nearby EMP or static discharge would take out the first LNA IC.

In the Winegard LNA200, it would most likely be Q2 even though it has 2 transient suppressors.











__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html

Last edited by rabbit73; 20-Apr-2019 at 6:25 PM. Reason: Added Q2 LNA IC specs
rabbit73 is offline   Reply With Quote
Old 7-May-2019, 4:17 PM   #5
dustyz
Junior Member
 
Join Date: Jan 2013
Location: KY
Posts: 29
Sorry for the late reply, but that is very helpful. Thanks for sharing. I will delve into my broken amps and see what I can find out.

I appreciate it.
dustyz is offline   Reply With Quote
Old 7-May-2019, 7:54 PM   #6
Tower Guy
Senior Member
 
Join Date: Dec 2009
Location: Delmar, NY
Posts: 1,164
The LNA-200 appears to amplify UHF and VHF separately. Q2 is the UHF amp. Q1 is the VHF amplifier. While both could be bad, if the amp works in VHF but not UHF, change only Q1. If it works on UHF but not VHF, change only Q2.
Tower Guy is offline   Reply With Quote
Old 7-May-2019, 7:57 PM   #7
Tower Guy
Senior Member
 
Join Date: Dec 2009
Location: Delmar, NY
Posts: 1,164
Q3 appears to be a voltage regulator for Q2. If the voltage on inductor L16 is not 3 volts +/-, change Q3.
Tower Guy is offline   Reply With Quote
Reply

Bookmarks

Go Back   TV Fool > Over The Air Services > Special Topics > Antennas


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off




All times are GMT. The time now is 3:30 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright © TV Fool, LLC