Realistic STA-52B Problems (Stereo Indicator & FM Oscillator Trimmer)

[Werkes]

I'm having a few problems with my STA-52B I picked up for a garage stereo. I got the whole exterior reconditioned but the interior is giving me problems.

The bulb for the stereo indicator didn't work, the manual says it's 6 V 60mA. So I wired in a 5mm red led with a 220 Ohm resistor on the positive lead. It works now but I have a problem. The LED is still super bright while tuning with static. Should a just submit and use a Christmas light?

Also, it says I should have an FM Oscillator Trimmer (TC 103) in the service manual but it isn't on my PCB. Also, the FM ANT (L 101) trimmer capacitor looks broken. I'm guessing these are unobtainium?

I'm hoping to find a place or person local by The Villages Florida that can help me get my FM aligned. I was going to have my buddy that does Air Force RF do it but he won't be here until November. I would tackle it myself but I feel like it's something you really need the proper equipment for. The Sencore SG-165 seems to be going for a lot right now & the cost of an OScope on top of that makes me even more unwilling.

Thanks.

 

[markn2wae]

I can't tell what is "broken" on the FM ant. trimmer, but the "missing" FM OSC. trimmer is at the top of the main tuner assembly and NOT on the PCB.

As for using the LED instead of a filament lamp, try putting a 100 OHM resistor ACROSS the lamp leads, then add your 220 Ohm resistor and led across the 100 Ohm resistor (same as you did before).

The reason the led lights on static is the circuit draws SOME current even when it "should be dark", the lamp needs higher current and stays dark, the led continues to light because it needs less current than the lamp (the 100 Ohm resistor "simulates" the standard lamps lower resistanc).

Mark T.

 

[Werkes]

I can't tell what is "broken" on the FM ant. trimmer, but the "missing" FM OSC. trimmer is at the top of the main tuner assembly and NOT on the PCB.

As for using the LED instead of a filament lamp, try putting a 100 OHM resistor ACROSS the lamp leads, then add your 220 Ohm resistor and led across the 100 Ohm resistor (same as you did before).

The reason the led lights on static is the circuit draws SOME current even when it "should be dark", the lamp needs higher current and stays dark, the led continues to light because it needs less current than the lamp (the 100 Ohm resistor "simulates" the standard lamps lower resistanc).

Mark T.

I'm going to try that with the LED, thanks for the suggestion! I tried a 100 Ohm and it helped a little but still occurs. I'll be going to my shop tomorrow and picking up my DMM (I borrowed a neighbors and it's one of those cheapy $3 ones, so bad), I have a suspicion this is way more than 6V & something is out of wack

Ah, I totally overlooked that 5th adjustment on the tuner, I looked at the diagram and seen TC 103 on the PCB in relation to where it is on the diagram. Thank you!

The little hex adjustment looks cracked/split. here's a close up.