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FM tuner alignment?

michiel - 2013-11-04 10:05

Hey Guys, I got this radio and the FM only gives white fm noise. It isn't receiving any station. Not even a little bit, just the same noise while turning the tuner knob. What could this be? Alignment maybe? The other lower bands are working fine, SW, LW, MW.

Any change I can allign it myself? Or do I need fancy equipment to do so? Is this the first time I gonna need a pro?

deliverance - 2013-11-04 10:19

it wont be alignment michiel as your receiving nothing get hold of schematic/service manual and go from there       

deliverance - 2013-11-04 10:25

just to add to do a alignment properly you need signal  generator, frequency counter, dvlm and all sorts but you can do a tweek here and there   .

michiel - 2013-11-04 10:29

Thanks Chris, I have the service manual. Will start with the voltages  

michiel - 2013-11-04 10:33

Originally Posted by deliverance:

just to add to do a alignment properly you need signal  generator, frequency counter, dvlm and all sorts but you can do a tweek here and there   .

I have a signal generator, frequency counter and scope, but I never used them for the higher frequencies. Don't now if they capable. If I only had some reception I could do some tweaking, but with totaly nothing is hard to do 

deliverance - 2013-11-04 10:38

Originally Posted by Michiel:

Thanks Chris, I have the service manual. Will start with the voltages  


good man thats the spirit    

seb968 - 2013-11-04 10:56

Hi Michiel

Very often the FM section of a radio has its own RF amplifier chip. This will be one of the first components after the antenna. These are vulnerable to static discharge particularly from severe lightening storms etc. There is also often a protection diode on the antenna but this won’t always save the chip. I have had several Sharp boomboxes that have had problems like this and they have been rectified by simply replacing the chip. The radio shouldn’t need re-alignment.

 

michiel - 2013-11-04 12:13

Thanks Seb! It's indeed a very simple tuner. Four transistors 2xFM RF, 1x FM OSC and 1x Mix in front of an IC. The IC is combined FM and AM and the am part is still working fine, so I doubt the ic is gone. But at least the ic is not obsolete, so that's nice  It's a Hitachi HA11251 ic in a JVC RC-550 box.

 

 

seb968 - 2013-11-04 12:34

Originally Posted by Michiel:

Thanks Seb! It's indeed a very simple tuner. Four transistors 2xFM RF, 1x FM OSC and 1x Mix in front of an IC. The IC is combined FM and AM and the am part is still working fine, so I doubt the ic is gone. But at least the ic is not obsolete, so that's nice  It's a Hitachi HA11251 ic in a JVC RC-550 box.

 

 

Ah, suppose I'd go for the RF transisters first, the closer to the FM antenna it is the more likely a failure has occured. On my little Sharp GF-4343 the ant goe's straight to an IC, a TA7335P I beleave this chip does what the two RF transistors do in yours. You could try and check them with the diode test on a muti meter. Between base and emitter and base and collector the transistors sould read approx. 0.6v one way and (swap the meter leads round) open circuit the other way. Hope this heps mate.

michiel - 2013-11-04 12:45

Thanks Seb!