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New to McIntosh, Tuner Issues

Freddie73 said:
Changed the opto-coupler and all back to normal.
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Might I have the part number for the opto coupler and did you purchase this from McIntosh? If not , where? This what mine looks like. Made by Mitsumi ( photocell module MPL-1011. I also saw on another site to install a 1k ( somewhere on the circuit board) resistor if an led type bulb is used. Was this done in your case and can someone chime in with this recommendation. Is this to alter the forward voltage?
Regards paul
 

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I just took my MR 78 to audio Classics. I’m only about 2 1/2 hours away so I dropped it off because I recently bought it and I wanted to put back into factory specs and they told me yeah it’s got this in this wrong, we can handle it so come back in 14 weeks so sometime mid October I hope to get it 4 to 600 bucks they told me.
 
lbcgav said:
They were XVive branded VTL5C9s.
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I see these on ebay. I am hoping someone chimes in with that 1k resistor recommendation. I believe its because its an led vs an incandescent bulb. I also saw where McIntosh may have these for $55 bucks or so.
 
paulram said:
I see these on ebay. I am hoping someone chimes in with that 1k resistor recommendation. I believe its because its an led vs an incandescent bulb. I also saw where McIntosh may have these for $55 bucks or so.
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I think the ones on eBay are counterfeit. They look different than the ones I received from Thonk.
 
Paulram, for the McIntosh MR74 the McIntosh replacement part number is 144-179-00. I purchased it from Audio Classics. I did not add a resistor as it is supposed to be a drop in replacement. I played my tuner for about 30 minutes after replacing as I will replace the electrolytic capacitors before long term playing.
 
Mine was about $55.00 plus tax and shipping. The original 144-014 has an incandescent bulb inside the replacement 144-179-00 is LED. It Was/Is a known issue with the MR74 that the incandescent bulb can burn out so McIntosh ( I have read) developed it as a drop in LED replacement specifically for the 144-014 knowing it requires different voltage. I read it did not require a resistor. I hope long term that proves to be the case.
Hopefully someone with more knowledge will chime in.
 
Paulram I see you previously posted that you have a McIntosh MX114 and I downloaded the schematic and it originally had a 114-013 opto-coupler that is replaced with the 144-179-00 according to AI. It looks as if yours has previously been replaced.
Do you know if that is the case?IMG_5849.png
 
Freddie73 said:
McIntosh might also have part number 144-179-00.
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Thank you for all your responses . The fm volume is ok on my unit ( MX114) , its just that there is no fm stereo and AI suggests that the optocoupler may not fix that issue. AI pointed to other components like a transistor ( forgot which). The photo that I posted of the coupler does indeed looks like a replacement.
 
I also read that a bad opto-coupler can cause low/no volume and no FM stereo. Mine had both extremely low volume and no stereo signal. I guess I can say I’d try the McIntosh replacement ( because it fixed my mr74) but it cost about $65.00 delivered. But when running right these are worth much more. Let us all know what happens.
 
Freddie73 said:
I also read that a bad opto-coupler can cause low/no volume and no FM stereo. Mine had both extremely low volume and no stereo signal. I guess I can say I’d try the McIntosh replacement ( because it fixed my mr74) but it cost about $65.00 delivered. But when running right these are worth much more. Let us all know what happens.
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I'll certainly order one and see what happens after installing it.
SaturationPt said:
“AI” is not a trained and experienced Technician nor Enginee
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Point taken!!
 
paulram said:
I see these on ebay. I am hoping someone chimes in with that 1k resistor recommendation. I believe its because its an led vs an incandescent bulb. I also saw where McIntosh may have these for $55 bucks or so.
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I received the optocoupler from Audio Classics and here is what it looks like. Note the rounded end is the LED side with the anode (+ve) lead wire being longer. The old style incandescent couplers appear not to exist anymore and there is nothing stamped on the part to suggest it is a VTL5C9 which my research suggests it should be. As far as I can tell the optocoupler resembles images I see with a google search and does not appear to
be a proprietary part. I am inclined to add the 1K resistor as outlined in a service bulletin ( 039406) from Mcintosh. One challenge I have ahead of me is to determine where to connect the anode of the LED to the circuit . One lead of the old coupler is connected to the collector of the Q103 transistor and the other to the muting switch , a capacitor to ground comes off this junction. I will elaborate with schematics soon and do note for those of you with the MR74 that the transistor Q designation in the MPX section is different, being the Q one hundred numbering in the MX114 and seemingly the 400 numbering for the MR74.
 

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From what I see this should be the positive lead ( circled in red ) on the mx 114 mpx board. Maybe more experienced members could chime in. IMG_5903.png
 
I installed the optocoupler and I am awaiting a transistor so I can remove the old one (Q101) as the emitter and base voltages were way off. Installing the
optocoupler did not solve the no fm stereo issue and research indicates that correct voltages from the said Q101transistor may rectify this. This is fun!
 
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