No stereo FM on Kr-7060

[Gertjan90]

Hi guys,

I recently picked up a Kr-7060 (same as 7600) in OK condition.
Everything works fine, except the FM stereo apparently.
I can tune in to FM stations beatifully, but they are all mono. This unit is supposed to automatically switch to stereo when detected, but that never happens. The stereo light never lights up and pressing the mono button doesn't alter the sound, so I don't think it's just a blown bulb.
I'm using a T-style 300ohm antenna and the signals I'm getting are plenty strong.

I have the service manual.

Does anyone have any experience with this receiver/ problem?

Any help is appreciated.

 

[hopjohn]

It could be one of many things gone wrong in the decoder section of the tuner. An alignment issue due to drift, a bad MPX IC, or possibly a bad or weak transistor or other component within the FM pilot circuit. You may also want to check that the FM muting is disengaged (you'll know it's off if there is static between stations) to ensure the problem doesn't exist there instead. One simple thing you can try to help further diagnose what's going on is to measure the voltage across the stereo lamp and compare it while tuned to a strong signal with the mono switch on and off. The differences in voltages could say something about how the mpx decoder is behaving.

 

[gort69]

Nice receiver - the KR-7060 is scarce.

- Sometimes it's hard to tell if you're actually receiving stereo, and listening through headphones makes it easier.

- Make certain the bulb isn't burned out. It's not too difficult to access and remove it and test it with a meter set to continuity. If you need help accessing the bulb, post back and I'll help with that.

- Once you are positive that the lamp is good and you are tuned to a known strong stereo station, usually an adjustment of the VCO (voltage controlled oscillator) will get you back in the game. In your service manual, locate the VCO trimmer - it is VRg2. It will be labeled VR2 on the tuner board, but the trimmer probably covers the writing. The s/m shows where it is. (I have seen these receivers with a different tuner board than what is listed in the manual - in any case VR2 is what you want to adjust)

Make a note of how trimmer is adjusted before you start. Use a non-conductive screwdriver or a metal one covered with heat shrink or elec tape, and slowly turn the trimmer one way or the other and see if the stereo lamp lights up. If it doesn't light going one direction try the other. Once it lights up keep going until it turns off again, then go back to roughly the middle of the "on" setting.

If adjusting the VCO doesn't solve the issue, move the trimmer back to where it was before you started, then punt.

 

[sregor]

+1 adjusting the VCO. You may want to start with deoxit or cleaner and work the VCO back an forth a couple of times.
Access to a scope? Check and see if signal at test point. There is a cap that can go open, causing no mpx. Cg44 Calls for polyester film, but any good quality cap will work.

 

[Gertjan90]

Thanks for the quick replies!

The bulb was burned out, but this wasn't the problem, unfortunately.
I replaced it with a known working one, but still no stereo.

I'll try adjusting the VCO next.

 

[Gertjan90]

Ok,
Before I even started adjusting, the stereo light suddenly started shining, but it was very hard to lock on to a station.
So I moved the VCO a bit and this became a bit better. Because I'm using a makeshift antenna on my work bench, I should be able to get stereo FM on my propper antenna.
But.. now my signal meter light blew ( was apparently on it's last legs anyway).
Is there a place where I can source bulbs for this unit?
I need two source selector lights and an 8V 0.3mA bulb for the meter.
The needle on the signal meter is also somewhat stuck and the tuning meter is missing altogether, so if anyone should happen to have these lying anound, I'd love to hear it!

 

[gort69]

Best for the meter (and dial) lamps are 8v 250ma wedge lamps. I doubt you'll find the original style. The 8v 50ma lamps for the indicators are still available in the original style. You can get both styles from this AK member https://sites.google.com/site/dgwojocom/ Both types are also available here: http://www.wjoe.com/diallamps.htm

 

[hopjohn]

Sometimes you can carefully clean meters such as this where there's is a bit of debris in them making them stick. Do this by removing the clear plastic cover (just held on by transparent tape) and using a bulb syringe (like that for a baby's nose) to gently blow some air at the needle base while preventing the needle from moving. I've had success with this in the past, and though its not always foolproof it's worth suggesting.