Help for "Stereo Led" on National Panasonic RX-7000FA

[floris1a]

Hello,
I am a boombox collector and recently I purchased a "National Panasonic RX-7000FA" with many defects.
I managed to fix many of the defects myself (I have a little experience).
The "RX-7000FA" model is rare and I could not find the service manual or a video demo for it.
It differs from "RX-7000" especially in the radio module (it also has SW).
The Stereo indicator LED stays ON, permanently as long as the Mono/Stereo switch is in the Stereo position, regardless of whether the radio station is stereo or not. Stereo broadcast stations reproduce them in stereo.
I looked for the defect, I didn't find anything and I think that's how it works.
Does anyone know if on this model the stereo LED stays on permanently as long as the Mono/Stereo switch is in the Stereo position regardless of whether the radio station is Stereo or Mono?
Thank you very much.

 

[hopey]

There is a trim pot that can be adjusted to set the bandwidth either side of the station.

 

[floris1a]

The problem is not with the trim. The LED also lights up when only the cassette player is working.

 

[hopey]

It's sensitivity might be related to recording from radio. If you find the pot and adjust it should go out between stations.

 

[Tinman]

I've never had that model but I'm assuming that it should only come on when stereo is detected.
It sounds like the led circuit could possibly be shorted.
The MPX ic controls the stereo led, I'd start looking there.
Get the number of the chip and look it up to help decipher which pins do what.
The RX-7000 should be similar enough that you might want to use that manual to help steer you in the right direction.
I just finished my Nat/Pan 5350, it was the worst experience I've had working on boomboxes.
I couldn't find a service manual for this one either so I occasionally used the Panasonic 5350 manual for some guidance.
My radio wouldn't work in FM stereo or ambience modes, just mono.

 

[AE_Stereo]

Just to confirm, as I see on my JDM RX-7000, the Mono/Stereo/Ambience switch on the RX-7000 is for altering sound from all sources, it is not specific to FM stereo. And there is only a FM Stereo indicator LED which illuminates with FM stereo reception, for which there is no separate Mono/Stereo control switch, (I believe, it is the 'FM Wireless' Band of the radio band switch plays FM in mono.). Am I right?

So in that case, either the Stereo LED has been rewired by someone else, or there is a fault in the FM signal strength detection circuit such as a failed capacitor.

 

[floris1a]

The radio block of the FM-7000FA is different from that of the FM-7000, apart from the fact that it has SW, the construction is also different. FM-7000FA does not have "FM Wireless". The LED also lights up when the cassette player is working with the switch set to stereo. My opinion is that the defect is from the integrated MPX, IC 502, BA1330, it powers the LED between stations even when I adjust the POT for 19KHz for any value. I checked and the led is connected correctly.

 

[AE_Stereo]

Please post a close-up photo of the Radio/Control Panel of your RX-7000.

 

[Superduper]

Regardless of the model, tuner stereo lights are always used as a guide to inform the user that FM "stereo" has been captured. There's no reason or point for the presence of an illuminated stereo light whenever the switch is flipped to stereo. A quick look at the knob tells as much whether the set is in stereo or other mode. I've been collecting stereos of all kinds for decades and have never seen a stereo with a led that illuminates just to tell you the mode you selected unless the led is right next to the switch in which case, it's kind of obvious that it's a selector indicator, not a "stereo" indicator.

The way most MPX circuits work in that era is that the stereo led receives current all the time. It illuminates when it is able to source ground, typically through an MPX control IC. The most likely culprit is a faulty MPX decoder chip but I've seen failures in adjacent components too, although usually any faulty resistors and caps associated with that circuit would prevent the led from illuminating rather than lighting it.

 

[floris1a]

This is how it looked when I bought it. Now it is disassembled and I am working on its repair. Repairs are a hobby, I can't occupy myself too much, so it takes time.
You're right, the LED is a "stereo indicator" and not a "selector indicator" and the RX-7000 is a serious radio, not a cheap one. In the meantime, I sent a message to a seller on eBay who sells an RX-7000F and he told me that the LED goes out between stations.

 

[AE_Stereo]

Thus, this is standard 4 band radio tuner with FM radio circuit in stereo (FM will play in stereo provided the signal is also in stereo!), with no separate switch for receiving FM in mono. The FM stereo indicator should light up only when FM signal of good strength captured in stereo.

Thumbs up for the RX-7000 branded as National Panasonic, which was the trademark used by Matsushita in the Middle East in those days.

 

[floris1a]

Now that the vacations are over, I also took care of my hobby. After I checked the capacitors connected to the MPX IC, I changed the IC with a new one and the LED went out completely. At the 19KHz setting, I also found the timer defective. Thank you all for your help.

 

[floris1a]

Excuse me "potentiometer trimmer" not timer I wanted to say

 

[Wes125]

ive had this problem with the stereo light staying on..it was the mono stereo switch contacts dirty. quick spray with the cleaner and worked the switch on off on off a few times and problem was solved