McIntosh MR80 Stereo Mode not working.
- Thread starter Drummerboy2
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Drummerboy2
Well-Known Member
Here's a pic of my MR80 in now working condition. 
Drummerboy2
Well-Known Member
Well, celebration short lived. Today was the 2nd time in 3 days that when I was listening to my MR80 today after a few hours it jumped to a lower band that was 87.7 where there was no music or anything just white noise, two days ago after I got it working it sudden jumped to a higher band 106.8 where there again no music just white noise. the Stereo mode is still working.
We have been having bad weather here in SD and it rained a lot the last two days. I have been listening for hours and no issues until those two and all good after. Now I'm wondering if those 4 pots where I made the adjustment R908 to get the 228KHz back work are drifting? I will double check again tomorrow for the 228KHz and the IC901 pins 2 and 3 for "0", might have to adjust that R905.
We have been having bad weather here in SD and it rained a lot the last two days. I have been listening for hours and no issues until those two and all good after. Now I'm wondering if those 4 pots where I made the adjustment R908 to get the 228KHz back work are drifting? I will double check again tomorrow for the 228KHz and the IC901 pins 2 and 3 for "0", might have to adjust that R905.
I doubt there’s any connection between that pot and the tuning issue.
The tuning is controlled by a completely separate voltage. If you hit scan up, that voltage will ramp up until it hits an active station and will stop once the station is tuned in. Likewise the voltage ramps down for scan down. For non-scan operations the tuning and preset pots control the tuning voltage.
It alsmot seems as though there’s a power supply issue or issue on that tuning board where the preset pots are. Particularly if it suddenly jumps (rather than stepping through the band gradually) I’d suspect something intermittently shorting or not making good contact.
The tuning is controlled by a completely separate voltage. If you hit scan up, that voltage will ramp up until it hits an active station and will stop once the station is tuned in. Likewise the voltage ramps down for scan down. For non-scan operations the tuning and preset pots control the tuning voltage.
It alsmot seems as though there’s a power supply issue or issue on that tuning board where the preset pots are. Particularly if it suddenly jumps (rather than stepping through the band gradually) I’d suspect something intermittently shorting or not making good contact.
Drummerboy2
Well-Known Member
I was just actually wondering about those 4 pots since the one I adjusted was a little on the non-linear side. and if they may need to be replaced. At work we used "Spectral" pots and on the older pcbs that had them they became nonlinear and would drift and had to change the venders due to this, it was for a pcb used in a life support device. So this is why I was wondering.
Stereo mode is still working great and since we were having rain/storms here in SoCal it was hard to get stations that are further out.
As for that Jumping stations, it has not done it since I reported it here. I do remember touching the Scan Up the first time it jumped to an upper non station just noise. and the the last time I remembered touching the Scan down hours earlier before it jumped to the Lower band. I had touched them because you mentioned that since the stereo was working maybe the Scan function be working also. No go.
The MR80 is sounding better and better and those upgrades are finally shinning through.
I did notice the Headphone Jack is loose and I do hear some faint hum when no signal is coming though, It seems like the power switch/volume control is the issue sine it slightly goes away as I turn up the volume on the headphone section. So I will look into that later, it doesn't happen on the "Fixed Output" only on the Headphone out. I can fix this issue.
I will have Mike Z. look at it soon for alignment but it's low priority right now.
Drummerboy2
Well-Known Member
So I did do an experiment with touching the Scan buttons and waiting, seem like when I do that about a few hours later it will jump or scan to the station depending on which Scan button I pressed. If I press the Upper Scan button it will go to the next station up, if press the Lower Scan button it goes to the lower station. Like I said, I have done this about 4 different times after I first turn on the tuner and this is what happens, it has never gone in the opposite direction than what Scan Button I have touched. So it seem like it's holding in a position and when it get the proper level/logic it then moves.
I will read more on this and see. It's not a big issue since it seems to be following what I push. Other than that, it has shown recently on first power up the station it was on when I turned off the power for the night before has shifted by .1 up or down and never more than that.
So once I fix the very faint humming in the headphone section I will then send it off to be aligned. I could like with it the way it is now but it deserves a alignment since power supply and other stuff may have been upgrade (Caps) that I don't know about.
The Stereo Mode is still working great.
I will read more on this and see. It's not a big issue since it seems to be following what I push. Other than that, it has shown recently on first power up the station it was on when I turned off the power for the night before has shifted by .1 up or down and never more than that.
So once I fix the very faint humming in the headphone section I will then send it off to be aligned. I could like with it the way it is now but it deserves a alignment since power supply and other stuff may have been upgrade (Caps) that I don't know about.
The Stereo Mode is still working great.
There is a touch sensitivity adjust pot on the display PC board. Might be a giant pain to get to it though. R509.
Strange that it happens some time after you hit the button.
The frequency being slightly off isn't a concern. This tuner is voltage tuned, ie voltage divided off a potentiometer tunes the oscillator, mixer, and front end filters. It'll change value slightly, as will the regulated voltage that feeds it, as it warms/cools. Also the AFC might have pulled to lock to a station and when you turn it off that AFC voltage disappears.... then when you turn it back on the station might be slightly out of the AFC capture range. Long story short, lots of reasons for it and none mean anything is wrong.
Strange that it happens some time after you hit the button.
The frequency being slightly off isn't a concern. This tuner is voltage tuned, ie voltage divided off a potentiometer tunes the oscillator, mixer, and front end filters. It'll change value slightly, as will the regulated voltage that feeds it, as it warms/cools. Also the AFC might have pulled to lock to a station and when you turn it off that AFC voltage disappears.... then when you turn it back on the station might be slightly out of the AFC capture range. Long story short, lots of reasons for it and none mean anything is wrong.
Drummerboy2
Well-Known Member
Ah, ok I get what you mean about the station being off by 0.1 when sometimes turn ON in the morning. Yesterday after wrote the latest things going on, it was on 96.4 so I set it to 96.5, after an hour I happened to look at the display and it was at 96.6. So maybe once everything settled in Voltage wise moved up which would have been at 96.5 if I would not have touched the dial. It remained dead on all day and night.
Everything else receiving stations wise work properly since that 228KHz adjustment you suggested. These other things are very minor and I could live with it MR-80 tuner as is, the stations come in very strong and are rock solid once tuned in. I have a tree that the branches have grown out and is directly in the signal path of the antenna for getting those LA stations that play Jazz. Once I cut them it will have a direct signal path to those stations. Between San Diego, LA, and Tijuana I have access to 5 stations which are not compressed San Diego City College, Long Beach City College, USC College, one Local Rock station, and the Station in Tijuana that plays really good music from Jazz, Funk, Fusion, R&B, Brazilian, and others types of music all uncompressed. This Shows me what the MR80 is capable of and I really enjoy listening to that variety of music and stations. Regular FM station come in clear with some sounding better than other but those 4 just kill them.
Hello,The frequency was off and measuring 225KHz. Took a few attempts but got into spec. Hopefully it holds there. I was remembering when I was adjusting that R908, that someone mentioned a long time ago on a thread to look into that Pot but didn't give any specifics and I didn't want to touch anything without know what I was doing. I took the measurements right at where the Jumper goes to the edge of the board.
Also, I remember replacing that cap right next to that jumper wire when I recapped the tuner after finding some caps not correct with the SM.
Audio is clear and sounds wonderful. I really don't care about the touch buttons for the Presets and Scan Up and Down.
I will play with the tuner for the rest of the days and see if I find any other issues but I'm a happy camper right now.
Here's a pic.
I recently picked up a MR80 that works well, except it does not tune to stereo. I am hoping to do this adjustment but I am not sure which pot is R908. Would you be able to clarify? Regards.
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Thank you for the info Bob!