Pioneer SX-1050 No FM Output

[lucapatt]

I have a Pioneer SX-1050 that I restored about two years ago (complete recap and replacement of troublesome transistors). At the time that I finished recapping, my FM/AM output worked perfectly. However, recently I noticed that I am unable to get any audio output with FM toggled despite a very centered tuning needle and nearly max signal strength w/ the stereo light on. I get AM output fine. There is also no difference with FM muting on our off. I do not suspect this is a dirty function switch as they have been cleaned thoroughly.

Pins 29 and 3 have their full 13V reference voltage.

Here is the HA1196 readings I have - they look pretty good to me:

Pin #	Ref	Measured
1	12.4	13.5
2	3	3.1
3	7.6	7.7
4	10.5	10.9
5	10.5	10.9
6	6.4	6.5
7	6.3	6.5
8	GND
9	0.8	0.8
10	2.4	2.4
11	2.4	2.4
12	2.4	2.4
13	2.4	2.4
14	2.4	2.4
15	3.1	2.4
16		4.9

Any help is much appreciated!

 

[kwayde]

Is there a signal to the caps (C70 & C47) before the low pass filter? Are there signals after the caps?

Signals to the low pass filter? Coming out of the low pass filter?

 

[zebulon1]

There's a reed relay at the output of the FM tuner.
The SX-1250 and Spec 2 has a similar circuit.
24v reed relay from Littlefuse HE751A2400, mounted dead bug style.
You can check for the signal at the input to the relay with a scope or your meter set to ACmv.

 

[painttoad]

The SX-1250 and Spec 2 has a similar circuit.

sx1010 as well.

i've been able to diagnose non working reed relays by dragging a magnet end to end. the magnet will engage/disengage it.

the why then has to be diagnosed.

 

[kwayde]

There's a reed relay at the output of the FM tuner.
The SX-1250 and Spec 2 has a similar circuit.
24v reed relay from Littlefuse HE751A2400, mounted dead bug style.
You can check for the signal at the input to the relay with a scope or your meter set to ACmv.

View attachment 3854184

Now that you mention this I remember having a bad one in mine years back.

 

[painttoad]

Now that you mention this I remember having a bad one in mine years back.

same relay as in the sx1010.

mine was only pulling 1 side in. when i used a magnet, i could pull in both channels.

 

[lucapatt]

Hey all! Thanks for the replies - I ended up figuring out the issue and feel like an idiot!

Is there a signal to the caps (C70 & C47) before the low pass filter? Are there signals after the caps?

Signals to the low pass filter? Coming out of the low pass filter?

I have a scope and was probing (C70 & C47) - these caps were replaced with WIMA film caps of respective uF during the restoration. My memory must have served me wrong with thinking FM functioned after recapping because I discovered that my replacement caps were installed in the wrong orientation. They should be bridging the circuit in parallel orientation with the low pass filter - not running North to South like pictured. Once swapped FM started working perfectly fine again.

Appreciate you steering my attention to the area I needed to look!

There's a reed relay at the output of the FM tuner.
The SX-1250 and Spec 2 has a similar circuit.
24v reed relay from Littlefuse HE751A2400, mounted dead bug style.
You can check for the signal at the input to the relay with a scope or your meter set to ACmv.

View attachment 3854184

The issue is corrected, but I wanted to clarify something with the reed relay - doesn't toggling FM muting off bypass the reed relay altogether?

 

[rcs16]

Look at the schematic, the FM muting relay contacts short the outputs to ground.