Marantz PMS7000
- Thread starter BoomboxLover48
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HI Bill,
I cleaned it well! It looks very good. I will measure and see for any breaks. Have you seen those 10K trimmers go bad? I never knew that.
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Hi Norm, I tried to connect parallel to the LED leads and that didn't show any voltage.
Imagine it was working well, then stopped and worked once again after going completely dead.
The radio reception don't sound in stereo with separation.
Wait, what did you do? And why?
I thought you were trying to determine whether or not the LED is still good. You should try to light it, and to do that, the simplest way is to probably just use a 1.5v battery. Solder leads to the battery, unless you have a single cell battery holder with already attached leads. Include a resistor in parallel, anything 270 - 470 ohm will probably do it, and probe to the led connections, see if it will light. For obvious reasons, observe polarity.
You just said something about showing voltage. What does that mean, are you measuring voltage across the led leads, and is this live? You do know that when you connect a voltmeter across the led leads, you are basically trying to measure voltage drop right? MPX circuits don't light leds like you normally imagine they would. It's not like the circuit captures stereo and then just sends 1.7v to the led, it's more complicated than that and the led (-) usually is not tethered to ground. Instead, it's sources ground through the MPX circuit, often just an IC.
I suggest you determine the following first:
(1) is LED working. (see test above)
(2) verify that the 19khz pot is working properly. To do this, use your DMM in ohm mode, and test from the leads at the extremes, that should tell you the pot ohm rating. Make sure it matches specs. Then measure from center lead to either extreme. Regardless of pot position, the sum of those 2 readings should equal the reading from end to end. For example if you conclude that the pot is a 5k unit, and you get 3.5k and 1.5k from the center lead to both of the other 2 leads, then the pot is good. Move the setting to another spot to confirm. If the pot is bad, replace before proceeding.
(3) I do not have a service manual, and don't want to download anything from that POS thieving website HFE. However, most boomboxes of that era utilize an MPX IC chip for the stereo decoding chores. It is most likely the closest IC to the adjustment and test points. Google the IC# and verify that it is the MPX IC. The appurtenant components are very important. Oftentimes, they'll get a bad connection due to poor solder joints. Reflow those. Also test the components that connect directly to the IC. There are usually a few resistors and capacitors. Make sure they are still good and within specs; if bad, replace. You may have to lift a leg to get an accurate reading. If all those checks out, then you may have a bad MPX IC. That is not uncommon. Replace.
Proper method of MPX adjustment is not by tuning to a strong station and turning pot until it lights. Lacking a stereo signal generator, find a stereo station that is close to the center of the tuning dial. Turn the pot slowly until you find the center point between when it lights and extinguishes. You need to do this from both directions and find the midpoint. If you adjust it using a very strong station, there is no guarantee that it will still be accurate for weak stations. Strong stations trigger the led much easier than weaker ones and have a wider latching spectrum, so choosing the strongest station isn't the best choice. Ideally, you'd tune to a quiet location near the center of the dial and inject a stereo signal to the tuned frequency, then make the adjustment using not the LED as a guide, but a frequency counter at the TP. Adjust pot until you get 19khz. Many decent DMMs will have a frequency counter mode, although they aren't as useful as a standalone frequency counter as DMM's don't have any way to adjust signal level threshold. Lastly, you should know that a tuner that is getting weak may not be able to trigger the stereo light. Is your tuner getting weak or are stations coming in strong?
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Thanks so much for the detail oriented reply Norm! Wow! Thanks for your time!
FM radio reception is very strong and clear with the Marantz. It was all working fine when the stereo LED started non functioning. It don't sound like stereo anymore and is all from the middle area of the boombox. Did the stereo detector circuit failed for some reason? I don't know. This is a beautiful boombox with super nice sound.
I was doing the wrong way unlike you mentioned while doing the trimmer adjustment. I will try exactly like you mentioned and see if that works. Basically I went to a strong station on the right far end around 106MHz and turned the trimmer both ways to see if the LED lights up.
I will try your recommendations and advice and get back soon.
Radio raheem
Requiem Æternam
only other thing i would suggest is to test the stereo separation on headphones my man while working on the tuner
May I ask you're opinion or anyone's here for that matter on how these TOTL large Marantz boxes stack up to the other high end boxes of other makes?? I have heard nothing but wonderful things on the build quality and feel but not much on the sound quality.
All opinions welcome!
(I hope you have been able to make more progress getting her back to 100%!!!)
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