Motorboating FM with MX110

Destructor

Super Member
The FM audio from my MX110 (Z) is oscillating or motorboating. All other inputs are fine, unit is dead quiet. The problem is noticable during "busy" musical pssages and singing. A DJ or talk radio it is not as noticable. Some time ago I replaced the 4 X 50 multi section cap with a new repro. and the smaller single electrolytic cap that comes off of that (forget value). The other two big caps remain. There is another small electrolytic paper covered cap inside that remains. Unit was working beautifully for the past 6 months or so, motorboating just started. Are there any common failure prone parts that I should replace in the FM section. I lack the ability to test other than checking voltages. I was going to have the unit's alignment checked at a shop. If I can not fix it myself I'll have the shop check it out. Any advice would be appriciated.
 
Would an alignment issue crop up suddenly as this seems to have done ? I suspect I need an alignment only because after my MR67 was aligned I had something to compare it to. Are there any tubes that would cause motorboating ?
 
Never had MX-110 on the bench and no scat handy. One of the tubes in the MPX section could cause it. Yes as tubes age and get weaker, the alignment will drift.

Just speaking from experience, when aligning many tube tuners if you take the 38Khz adjustment off, it will oscilate and cause a motorboating sound.

X
 
As a general rule when you change the demux tubes in any of the McIntosh tube tuners you should realign the demultiplex or you will not have optimum separation.
 
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