MAC 1900 receiver - FM MPX (Stereo) light does not on

[anti-doom]

MAC 1900 FM MPX light does not turn on. Lamp is good. Got 0 V at the lamp socket which connects to C of Q502 on PS board.

At Q502, got 37V at both B and E which are correct with schematic. Schematic shows B of Q502 connects to pin 14 of IF MPX board but it actually connects to pin 15 of IF board. Please look at the attached image.

Can anyone explain how FM MPX stereo light circuit works and hox to fix if light does not turn on?

Thank you.

 

[mea2112]

This is probably obvious but make sure your FM antenna is connected properly and is working well and the Stereo button is activated..

 

[anti-doom]

This is probably obvious but make sure your FM antenna is connected properly and is working well and the Stereo button is activated..

Yes, antenna is connected and Stereo button is activated.
Thanks

 

[anti-doom]

FM MPX light is on.
It was Q106 shorted.
Q106 is132-075 part which can be replaced by 2SC2240BL (120V/120V/5V/0.1A/0.3W/hFE min 350) which then can be replaced by ZTX694B (120V/120V/5V/0.5A/1W/hFE min 500).

Still looking fot sub of 132-077. Please let me know.
Thanks.

 

[ramjet]

Siemens BC148C is the original, available on eBay now. Do you have this? http://www.tubebooks.org/file_downloads/McIntosh/semiconductor_data.pdf

 

[w3jn]

Mc cross references sez Siemens BC148C

 

[anti-doom]

Thanks for the info. Now I will be looking for BC148C. Worry about fake on Bay but will try.
Thanks

 

[ramjet]

NTE123AP, BC238C, 2N3904, 2N3568, etc.

 

[anti-doom]

NTE123AP, BC238C, 2N3904, 2N3568, etc.

That's what I am looking for. Thanks a lot.

 

[Fairlane]

https://audiokarma.org/forums/index.php?threads/mac-1900-fm-mpx-light-problem.971921/#post-15070914

I had the same problem and its a simple fix with the right transistor.

 

[anti-doom]

https://audiokarma.org/forums/index.php?threads/mac-1900-fm-mpx-light-problem.971921/#post-15070914

I had the same problem and its a simple fix with the right transistor.

Thanks. I read that post too.

 

[IASTM]

FM MPX light is on.
It was Q106 shorted.
Q106 is132-075 part which can be replaced by 2SC2240BL (120V/120V/5V/0.1A/0.3W/hFE min 350) which then can be replaced by ZTX694B (120V/120V/5V/0.5A/1W/hFE min 500).

Still looking fot sub of 132-077. Please let me know.
Thanks.

So what’s the best replacement for Q106?

 

[ArturoARTART]

Sorry, does anyone have a guide to replacing this lamp (FM MPX)? thanks