Wondering if anyone can help guide me on something as tuners are admittedly my biggest weakness when restoring vintage audio.
I have a Sony STR-6065 that was dead with 1 channel completely toast; rebuilt the power supply and power amp board, new filter caps, new outputs... everything works and sounds great, except FM. When in FM mode, at first it was doing nothing. No sound, nothing. I threw new caps in the MPX board since it was already open and now I am hearing something, and it's tuning and pulling stations, but only at a fraction of the volume of everything else. I pulled the IF board and started re-working that, but something keeps pushing me back to the MPX board.
In the schematic it looks like the MPX board goes direct out to the power amplifier. I'm still trying to get my head around the block diagram (again, tuners are a weakness). Would it be most likely if I'm getting any type of volume drop before it hits the amp section, it would be in that board?
I also just noticed that there are a few tantalum caps in the MPX that I didn't change and should pull.
I have a Sony STR-6065 that was dead with 1 channel completely toast; rebuilt the power supply and power amp board, new filter caps, new outputs... everything works and sounds great, except FM. When in FM mode, at first it was doing nothing. No sound, nothing. I threw new caps in the MPX board since it was already open and now I am hearing something, and it's tuning and pulling stations, but only at a fraction of the volume of everything else. I pulled the IF board and started re-working that, but something keeps pushing me back to the MPX board.
In the schematic it looks like the MPX board goes direct out to the power amplifier. I'm still trying to get my head around the block diagram (again, tuners are a weakness). Would it be most likely if I'm getting any type of volume drop before it hits the amp section, it would be in that board?
I also just noticed that there are a few tantalum caps in the MPX that I didn't change and should pull.
Have you got an oscilloscope and are their any signal levels indicated on the schematic you have? If so, you could measure whether the MPX signal has a reasonable level.
First bypass mpx, use mono signal going to mpx, check its sound quality and volume.
This signal has to be normal few hundred mV.
If mpx is working well, mono signal going into the stereodecoder should be the same signal level as going out.
This signal has to be normal few hundred mV.
If mpx is working well, mono signal going into the stereodecoder should be the same signal level as going out.
Ok, let me just make sure I understand what you mean. Do I disconnect the input of the MPX board, and inject say a 1khz signal into the board and see if it's coming out the same?
No, devinitely not. I meant that before you even start poking in stereodecoder, you need to know if front end and demodulator are working correctly. That is if there is actually correct strong signal going out from demodulator.
Yeahhh, so even that is over my head... does it help that once I land on a stereo station, i can flip the muting on and it stays on? It literally sounds like the FM level is just way lower than every other function (including AM)
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I'm really junior, so take my advice with a pinch of salt but what I can offer is to look at the values I have on a similar unit (Sony STR-6045). See this post.
If you have a strong signal (the stereo light should turn on), then it could be the muting circuit that is always on. From the service manual:
Verify if Q209 is cut off or not and that Q207 is conducting.
If you have a strong signal (the stereo light should turn on), then it could be the muting circuit that is always on. From the service manual:
Verify if Q209 is cut off or not and that Q207 is conducting.
Hey any advice is better than none. I just buttoned this unit up last night and decided to leave the FM circuit alone. I will never listen to FM and this was more of a completist thing than a practical thing. I did pull those FETs from the board and tested them with my meter and using a Peak Atlas just to see if they were shorted and they seemed good so I put them back in.