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DPete27
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Help Fixing FM Tuner Board

Sat Mar 28, 2020 4:57 pm

I've had this JVC MX GT700 stereo for 16+ years. Still enjoying it.

A long while ago, it stopped receiving any FM stations >95MHz.

Today, I finally cracked it open to discover my suspicion is true. The FM antenna jack shorted out:
Image

Image
(image links may get broken, I'll make sure to check back periodically)

I'm having a hard time locating this part. Would like to know if there's any way I can remedy the situation DIY style?
I don't really know how to "read" PCBs, but it seems the dark green lines are insulators. Can I simply solder in a jumper wire?
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just brew it!
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Re: Help Fixing FM Tuner Board

Sat Mar 28, 2020 6:01 pm

If that was due to induced current from a nearby lightning strike, it probably took some other stuff with it when it fried.
Nostalgia isn't what it used to be.
 
DPete27
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Re: Help Fixing FM Tuner Board

Sat Mar 28, 2020 8:21 pm

The stereo works perfectly except for the lack of ability to detect stations above 95MHz. I've also done a cursory inspection for other signs of shorts or damaged/bulged components and haven't found any yet. Let's just assume this was the only casualty.

It looks like the board lead between the antenna solder point and that pin down and to the left of it just disintegrated. Wondering if I should just solder a jumper wire between those two pins? I don't....think... that the black soot on the pins below the antenna pin represent any actual damage.... those three pins are all part of the same turny jigger(?) so that could be my next stop if the jumper wire doesn't fix the problem.
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SecretSquirrel
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Re: Help Fixing FM Tuner Board

Sat Mar 28, 2020 10:20 pm

JBI is likely right. Enough of a current to leave a burn mark, melt solder, and blow a trace likely took out the pre-amp/tuner (the thing in the metal box) and probably the filter crystal and probably the receiver chip too.

That said, lightning does the strangest things and if you have a soldering iron handy, it won't take you much more than a few seconds to put put a jumper in place to fix the trace. Maybe you get luck.

Image

The red line is what you need to connect.

--SS
 
SecretSquirrel
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Re: Help Fixing FM Tuner Board

Sat Mar 28, 2020 10:42 pm

A bit of searching and it looks like some Samsung tuner boards might be compatible, but its gonna be a shot in the dark and cost $50-$75 to find out. :(

For that price, you can pick up a component tuner on ebay and connect it to the aux in, assuming the system has one.

--SS
 
Captain Ned
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Re: Help Fixing FM Tuner Board

Sat Mar 28, 2020 11:10 pm

Not to be a PITA, but terrestrial FM has been a loudness war wasteland for at least a decade and public radio is usually south of 95.
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JustAnEngineer
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Re: Help Fixing FM Tuner Board

Sun Mar 29, 2020 4:58 am

A $20 FM radio + digital TV tuner USB stick would be an inexpensive replacement.
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DPete27
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Re: Help Fixing FM Tuner Board

Sun Mar 29, 2020 11:37 am

I'm just kinda sick of listening to the local rap station. That's not really my genre of choice in the first place. Before our recent move across town, I could get a good hard rock station which I enjoy.

I'll give the jumper wire a shot today. Just wanted someone more knowledgeable to confirm my assumption. Thanks SS.

Will report back with results.
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DPete27
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Re: Help Fixing FM Tuner Board

Sun Mar 29, 2020 2:57 pm

Gonna call this one a success! Jumper wire worked. Picks up full FM range.

I've probably used up all my repair luck for the foreseeable future having done this AND successfully baking my TV motherboard earlier this week...
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Re: Help Fixing FM Tuner Board

Sun Mar 29, 2020 3:08 pm

Cool. Always nice when it is something simple. Still surprised that something serious enough to fry a PCB trace didn't take something else with it.
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SecretSquirrel
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Re: Help Fixing FM Tuner Board

Mon Mar 30, 2020 7:26 am

just brew it! wrote:
Cool. Always nice when it is something simple. Still surprised that something serious enough to fry a PCB trace didn't take something else with it.


Lightning is a weird beast. But, I agree with you -- pretty surprising.

--SS

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