kr-70 help/service manual

biggal76

Active Member
Hi,
I recently picked up a KR-70. It was working well but now the FM Stereo is not kicking in. I originally thought it was the lightbulb, but it is the whole stereo circuit as flipping the switch on the front panel does not change the sound. I cannot find a service manual anywhere online. Does anyone have one or know what to check first?
 
Which circuit board would control stereo/mono? Is it on the preamp board? I doubt MPX board since it seems to be a problem on any input, not just FM, right? I'm still pretty new to this stuff but have had some good luck fixing a few things lately and would like to get this resolved.
Thanks
 
try one input into aux.. say left first then right .. see if sound comes out of both channels in stereo mode ..also see if balance is working correctly .
 
Pete, Thank you for responding. I just did what you asked. It looks like maybe it is just an FM issue. When I only have one input, sound only comes out one side in stereo and both in mono. Balance works properly. So is this likely on the IF or the MPX board? The IF board is identical and the MPX board is very very similar to the KR-77 which I have the service manual for (link in my 2nd post). Any advice on where to go next?
 
so you are getting both channels mixed in mono tuner only driving left right main amps ? and balance working ?
does this also happen with am or fm only ?
 
This unit does not have AM (I've never seen a receiver without AM before this one). The FM Stereo light does not have voltage to it (well, it has something like 0.08V) and I cannot hear a difference when going from stereo to mono using the switch, so I assume I'm getting both channels mixed. Balance will fade from left to right normally.
 
is there a fm mute ? not that i think its that ..just getting an idea of it .
my first thoughts are antenna problem.. i guess you ruled that out though .
must admit i am not that well clued up on fm circuitry . i sort of have a basic understanding that's all .
 
Pete,
No mute switch. Thanks for helping me figure out that it is just in the FM and ruling out the preamp board. Hopefully someone else can help me narrow down if its the MPX board or IF board. What does the IF board control? I assume it's the MPX board.
 
I don't quite understand what you are asking. There are two leads to the bulb. I connected the meter to both leads and it only reads .08V
It was working properly and all of a sudden the bulb went out. I could retune back to the station and it would come on for a second or two and then go out. It did that several times and now does not work at all.
 
The MPX board on this schematic is very similar to mine. It's the same part # but with a different letter at the end and looks the same at a glance. You have to register at Hifiengine.com to download it, but that site is a great resource to use and has service manuals for tons of equipment. I've found the forum here to be more helpful, but the library of manuals there seems to have a lot more.

http://www.hifiengine.com/manual_lib...od/kr-77.shtml
 
Oh, I couldn't find that manual anywhere. I searched a lot. Maybe your UK search engines are better than Google?
 
i use google ...searched for "kr-70 service manual " was seventh down in list ..
looks like you have a few things there with voltages to check ..
 
could be as simple as a shorted cap . or maybe needs a slight adjustment .few voltage checks should find it .
 
Thanks for your help. I'll probably be able to figure it out but might be a while as I'm going out of town for a week soon.
 
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