Ray Gianelli
Super Member
Several years ago a friend brought by 2 Kenwood KR-9600's. According to him, one had one channel out and the other had FM issues. The one with a channel out had a bad TA-200W output IC that appears to be NLA, so I focused on the other one.
The FM didn't pick up any stations, so I figured I'd just swap the tuner. Still nothing, so I set it aside to focus on the backlog piling up around my bench.
Fast forward several years. I now have a spectrum analyzer and an AM/FM stereo signal generator. My friend said he has someone who wants to buy a KR-9600, and asked me to revisit it.
I injected a an unmodulated signal into the antenna terminal from the generator. I took a look at the IF on the main board, and I could see the IF signal, but still couldn't hear anything. I started checking the op amp outputs after the ceramic filters, and saw good signal out of both op amp outputs, but nothing going into the FM IF chip. Problem turned out to be a bad ceramic filter, which had a lead rotted off of it. I replaced it with one from the donor unit, and now got a few stations, but nowhere near what I should have gotten.
I took the tuner I had pulled out of the unit I'm fixing and put it on the bench. I hooked it up to my bench power supply, signal generator and spectrum analyzer. The IF coming out of the tuner was way higher than what I was seeing when measuring the one in the receiver. I put it back in, and all was good.
The moral of the story is that unless you have a way to see what you're doing, you may make thing worse instead of better. Once I had the necessary test equipment it was relatively easy to see what was wrong.
Here's pics of the old tuner on the bench. I didn't take any pics of the other one, and it's already with its (delighted) new owner. The old tuner had to have the signal from the generator cranked up to pass any signal.
The FM didn't pick up any stations, so I figured I'd just swap the tuner. Still nothing, so I set it aside to focus on the backlog piling up around my bench.
Fast forward several years. I now have a spectrum analyzer and an AM/FM stereo signal generator. My friend said he has someone who wants to buy a KR-9600, and asked me to revisit it.
I injected a an unmodulated signal into the antenna terminal from the generator. I took a look at the IF on the main board, and I could see the IF signal, but still couldn't hear anything. I started checking the op amp outputs after the ceramic filters, and saw good signal out of both op amp outputs, but nothing going into the FM IF chip. Problem turned out to be a bad ceramic filter, which had a lead rotted off of it. I replaced it with one from the donor unit, and now got a few stations, but nowhere near what I should have gotten.
I took the tuner I had pulled out of the unit I'm fixing and put it on the bench. I hooked it up to my bench power supply, signal generator and spectrum analyzer. The IF coming out of the tuner was way higher than what I was seeing when measuring the one in the receiver. I put it back in, and all was good.
The moral of the story is that unless you have a way to see what you're doing, you may make thing worse instead of better. Once I had the necessary test equipment it was relatively easy to see what was wrong.
Here's pics of the old tuner on the bench. I didn't take any pics of the other one, and it's already with its (delighted) new owner. The old tuner had to have the signal from the generator cranked up to pass any signal.