HFU HF Underground
Technical Topics => Equipment => Topic started by: Looking-Glass on January 31, 2018, 0342 UTC
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Have a Tecsun 2000 which is just under two years old. Last year, around January/February I noticed a hash/crud/snow type noise at the very bottom of the FM band, it pins the 'S' meter.
Well, this noise is creeping every so slowly up the band and has reached 91.3MHz FM BBC and has now made that station unreadable.
Nothing below 91.3MHz is heard, this noise is more than likely generated from the insides of the radio itself, it is on the move ever so slowly up the band, nothing below 91.3MHz can be heard, just covered in wall to wall noise.
Any one else experienced this problem with the Tecsun-2000 or its Grundig variant?
I had my doubts about buying this Chinese made radio in the beginning, also have BFO drift problems too, what next? >:(
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Got the Satellit 750 here. Have read about problems with the BFO drift with this radio but have never had any of the problems that you describe. However, have always run mine on 4 "D" cells. Your Tecsun has a built-in supply that runs off of 220v mains. You may want to try running on pure DC ("D" cells) instead and see what happens.
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It always runs on the four "D" cell batteries, so problems is not caused by AC mains power.
I use it as a bed side radio due to its size and good frequency coverage. Basically, it's a useless piece of junk when it comes to serious DXing on Utility bands where CW and SSB modes are utilised in the majority of listening.
Great radio receiver on the FM band, but that noise is creeping right up the band over the past 12 months, has wiped out my BBC on 91.3MHz FM and it still slowly moving up the band, mystery.
Tempted to pull the thing to pieces and see what I come across, being made in China I shudder to look in the back! :o
If I find something new/rare I usually get up and go to the shack and monitor via the Yaesu FT-2000D base radio for better reception qualities and frequency accuracy.
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Since you think the noise is internal to the radio, it sounds like you may have a component gradually changing value. Capacitors (especially electrolytic) are the usual suspects but could be anything. Unfortunately, have not been able to locate a service manual or schematic for this radio. So, a more brute force form of troubleshooting may be necessary. Many times a flaky component can be located by use of a can of circuit freeze spray or alternately with heat from a hair dryer with some kind of a fabricated nozzle to direct the heat at suspect components. Also, a thorough inspection for bad, cold solder joints can sometimes detect a problem. Unplug and reseat any headers or other connectors. Even just tapping various components with the handle of a screwdriver can reveal a problem. None of this is very scientific but under the circumstances it looks like you are at the point of tearing into it anyway so, go for it. This sounds crude but a lot of radios have been fixed this way.
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L-G,
Have you had a chance to troubleshoot that radio?
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Not as yet, being doing near 12 hours shifts at work so sleeping most of the time when at home, or catching up on laundry and other household chores.
The BFO issue seems to have settled down for some unknown reason, sitting in same position now and not deviating.
Might have a go at it today before getting ready for work... 8)
Had a go at it and finally got in, heaps of screws to remove, including one hidden under a silver "checked" sticker, and one deep inside the D battery compartment.
Will return with findings... ::)
Circuit board is very cluttered and everything jammed up close together, didn't bother taking it out as afraid might not be able to get the screws holding it back in properly. Track circuit very small and couldn't get my meter ends to reliably sit as ends too big for this circuitry. Soldering in general is reasonably neat, unlike some Chinese boards I have seen with solder splashes everywhere this one is pretty good and clean.
Plug ins quite secure, disconnected and reconnected to make sure, gave the board a quick swipe with a tooth brush, very little dust or solder flicks. Gave the boards a little wiggle, all seemed secure in connection.
Put it all back together and up and running, reset as it went to default settings, FM band problem still there, huge noise up to 92MHz now. Don't have time or patience to totally dismantle and run the meter over it, another day maybe? ;)
PS: Tried to post a pic I took of circuit board but attachment would not load onto this page (JPEG).
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Circuit board is very cluttered and everything jammed up close together, didn't bother taking it out as afraid might not be able to get the screws holding it back in properly. Track circuit very small and couldn't get my meter ends to reliably sit as ends too big for this circuitry. Soldering in general is reasonably neat, unlike some Chinese boards I have seen with solder splashes everywhere this one is pretty good and clean.
Plug ins quite secure, disconnected and reconnected to make sure, gave the board a quick swipe with a tooth brush, very little dust or solder flicks. Gave the boards a little wiggle, all seemed secure in connection.
Put it all back together and up and running, reset as it went to default settings, FM band problem still there, huge noise up to 92MHz now. Don't have time or patience to totally dismantle and run the meter over it, another day maybe? ;)
PS: Tried to post a pic I took of circuit board but attachment would not load onto this page (JPEG).
Well, sounds like you did all you could to make sure all is OK mechanically and connections are secure.
Next step would be to hunt for and isolate a component that may be changing value when you get enough time and nerve to dive back into the radio.
Good luck, let us know what you may find.