Luxman R-115 troubleshoot

[MusicCity]

Saw a few Luxman R-115/117 threads here and thought I'd seek some expert guidance. Was all-in on Luxman back in the late 80's, with two R-115s, a DZ-111, a K-105 cassette deck, and the factory remote repeater. Drove everything from some Klipsch Heresys to some Maggie 1.6s with ease. One of the R-115s still operates just fine. The other will only play a signal fed through the CD connection and then only when CD Direct is switched on. With CD Direct on, it will play fine sans the typical scratchy volume knob/uneven output issue detailed elsewhere on this forum. If the normal CD input is selected without CD Direct on, you can very faintly hear the signal. I mean very faintly. Like turn it all the way up and set you ear next to the speaker. Otherwise nothing. Won't even send AM radio static to the speakers. Doesn't matter if the A or B speaker posts are used.

I plan to get around to the volume knob issue if the main input/output issue can be corrected. Otherwise, this one goes back to the closet or onto eBay as a parts donor. Welcome any ideas. Experienced auto mechanic. Very inexperienced electronics repair guy, but I do own a can of Deox-it!

 

[AnalogSteph]

Try some bridges (RCA cable) between SIGNAL PROCESSOR OUT and IN jacks. There's normally a switch bypassing the loop when nothing is plugged in but it might be badly oxidized.

If that's not it, odds are you've got a bad input selector IC (IC381 = TC9163N). These are kind of sensitive, and there appears to be no input protection whatsoever in this model (quite the oversight). If any of the inputs has ever been subjected to voltages outside the DC supplies, and that easily happens with mains leakage and stuff when plugging things in, the IC could easily have been zapped.

BTW, this one's got a pretty fancy tuner section for a receiver. 5-gang frontend with RF AGC, 2 MLs in wide + another MZ1 in narrow, so all GDT filters (no surprise then that a review found low distortion, even if I suspect that even Narrow isn't exactly the pinnacle of selectivity and rather ought to be called Normal in return). Even the AM still sports a dedicated RF preamp and a 4-element ceramic filter, either of which was becoming a rare sight even in dedicated tuners at the time.