From: No.Spam@No.Where.com   
      
   "Adamfarber"  wrote in message   
   news:Adamfarber.65d1add@audiobanter.com...   
   >   
   > 'Fred[_12_ Wrote:   
   >> ;911336']"Adamfarber"  wrote in   
   >> message news:Adamfarber.65c721d@audiobanter.com...-   
   >> >   
   >> > 'Fred[_12_ Wrote:-   
   >> >> ;911292']"Adamfarber"  wrote in   
   >> >> message news:Adamfarber.65bc95d@audiobanter.com...--   
   >> >> >   
   >> >> > David Nebenzahl;911263 Wrote:-   
   >> >> >> On 6/13/2010 12:56 PM Adamfarber spake thus:   
   >> >> >> --   
   >> >> >> > Hi Mark, I unhooked everything and hooked up a speaker to one   
   >> of-   
   >> >> the-   
   >> >> >> > outputs and listened to FM and I still heard the him. Thanks,-   
   >> >> Adam---   
   >> >> >>   
   >> >> >> The "him"?   
   >> >> >> Oh, you must mean the "hymn".   
   >> >> >>   
   >> >> >>   
   >> >> >> Whoops, meant HUM, thanks, Adam---   
   >> >>   
   >> >> Most likely a cap in one of the low voltage supplies has failed,   
   >> >> feeding unfiltered   
   >> >> DC to a regulator which cannot maintain smooth output voltage   
   >> because   
   >> >> the input   
   >> >> is going to zero 120 times a second.   
   >> >>   
   >> >> You have to be a technician with troubleshooting skills, experience   
   >> >> with AV receivers,   
   >> >> test equipment and service information to fix this.  Assuming   
   >> that's   
   >> >> not you, the unit   
   >> >> needs to go to a Yamaha warranty station for repair (Yamaha's   
   >> warranty   
   >> >> stations have   
   >> >> access not just to service manuals but also to confidential service   
   >> >> bulletins, and more   
   >> >> importantly they have access to the technical staff at Yamaha, which   
   >> is   
   >> >> the only really   
   >> >> competent technical staff in the business).  I can call Allen at   
   >> >> Yamaha, give him the   
   >> >> model number, and he'll tell me what the problem is and how to fix   
   >> it   
   >> >> because he and his   
   >> >> staff know their equipment that well.   
   >> >>   
   >> >> Obviously, I work for a Yamaha warranty station.  That's the only   
   >> >> company we still do   
   >> >> warranty audio work for, because it's the only one with a staff   
   >> that   
   >> >> knows a damn thing   
   >> >> about their product.  Well, them and McIntosh, but there are no Mac   
   >> >> dealers around here,   
   >> >> so they don't figure they need a warranty station here (Reno, NV).   
   >> >>   
   >> >> Fred   
   >> >>   
   >> >>   
   >> >> Hey Fred, thanks for the post. I am somewhat handy, if someone   
   >> could   
   >> >> narrow down which part(s) may be suspect I will replace them so any   
   >> >> help you could give me would be GREAT!  Adam--   
   >>   
   >> I'll check the service manual & bulletins when I get back to work (I'm   
   >> out with   
   >> the flu at the moment, and don't know for sure when that will be;   
   >> sometime in   
   >> the next day or three) and see if I can give you any worth while   
   >> advice.  Some   
   >> models are damn near impossible to take apart and get back together   
   >> without   
   >> the manual.  There can be 20 or more cables that have to be unplugged   
   >> and   
   >> then plugged back in to the right socket on the right board on   
   >> reassembly, just   
   >> to get to the board(s) you need to work on.  I'm assuming you want to   
   >> try a   
   >> shotgun approach and just replace every cap that could be causing the   
   >> problem.   
   >> It'd take a 'scope to figure out what cap *is* the problem.   
   >>   
   >> Watch this thread; I'll post again when I have some information for   
   >> you.   
   >>   
   >> Fred   
   >>   
   >> Shall do Fred, thanks again for trying!  Adam   
      
   Hi Adam,   
      
   Finally got back to work today, and had a look at the service manual.   
      
   First, you want to check the + & - voltages to the output stage.  To do this,   
   you'll need a Digital Multi-Meter (DVM).  You want to check the voltage from   
   chassis ground to the collectors of any two adjacent output transistors in the   
   power amp with the unit powered up.  Be careful not to let the meter probe   
   touch anything else while doing this, or you'll get a big arc and blown fuses   
   or   
   worse.  The exact voltage will depend on your line voltage and the setting of   
   the 4/8 ohm switch on the rear panel; the range is approximately +/- 40V to   
   +/- 70V.  What's important is that the + voltage equals the - voltage within a   
   volt or two.  If the voltages are not nearly equal, the main filter cap for the   
   lower of the two voltages is probably bad.  Those caps are on the Main (3)   
   board at the left rear of the unit.   
      
   It the unit passes that test, one of the following capacitors is probably bad,   
   and without a scope the only way to proceed is to obtain replacements for   
   all of them and replace them all.   
      
   On the Power (5) board, in the left front of the unit, mounted on the power   
   xfmr   
   secondary: C451 & 452, 330uf @ 50V.  C453 & 455, 4700uf @ 25V.  C458 &   
   463, 4700uf @ 16V.  Lastly, on the Main (3) board previously mentioned, C760   
   & 761, 100uf @ 50V.   
      
   If replacing these caps doesn't eliminate the hum, or if all this sounds way   
   over   
   your head, it's either off to a warranty station with the unit, or off to the   
   electronics store in search of a replacement.  I would expect repair to cost   
   between $100 & $200.  This is a pretty old unit; the service manual was printed   
   on paper.  These days everything is in PDF on the computer.   
      
   Hope this helps,   
      
   Fred   
      
      
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