Realistic STA-850 Stereo Receiver Problem FM in mono not stereo

[slobrain]

Hey folks,
I picked up a Realistic STA-850 stereo receiver recently and found the FM will not go into stereo mode, it only stays in mono.
I know these old tuners drift but wondering if anyone here has any working knowledge of this model receiver and a fix? adjustments? chips going bad? caps?

Thanks

 

[chazix]

If you're looking for a quick 'n' dirty DIY, you could try a seat-of-the-pants adjustment of the stereo decoder's free-running frequency. Misadjustment of same is a common cause of no stereo.

Tune to a strong station that you know is broadcasting in stereo. Take note of the original position of trimpot VR205. Turn the pot slowly through its range and see if stereo happens.

If it does, repeat the exercise, but note the two positions of the pot where stereo just starts to work as you turn the pot from either extreme. Leave the pot in the middle of those two positions.

If it doesn't, you will probably need the assistance of someone who's equipped to do tuner repairs and adjustments. Restore the pot to its original position.

Service manual is available on hifiengine and probably other places. If you have any trouble locating VR205, the manual will help.

HTH,

chazix

 

[Bruno Primas]

Not familiar with this model, but on a lower-powered Realistic I owned, if the stereo indicator lamp is burned-out, FM will not be in stereo. Check the lamp to see if it's good.

 

[slobrain]

Thanks for the information guys. So the lamp affects the FM stereo mode? BTW, who makes the Realistic receivers from the 80s? someone said it was Foster, some say its just different manufacturers thru the years. This one looks to be made by Technics by the build quality.

 

[Skywatcher]

Thanks for the information guys. So the lamp affects the FM stereo mode? BTW, who makes the Realistic receivers from the 80s? someone said it was Foster, some say its just different manufacturers thru the years. This one looks to be made by Technics by the build quality.

The stereo indicator light is an LED and is turned on by pin 9 of IC202. So it's not a lamp issue. Though Bruno Primas is correct that some do need the resistance of a filament bulb to complete the circuit. If you're not getting stereo in FM, you may just have too weak a signal, or someone needs to connect it to the proper equipment to determine the problem, and see if it has an actual problem (dried out caps, dry solder joint, bad IC, etc), or just needs a slight adjustment.