Sansui QRX 5500 quadrophonic receiver one channel is out but then an accident brought it b...

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This is my own receiver. It is mounted and wired into my home entertainment
 system cabinet. I rescued it from the junk pile about 35 years ago and for
 the first ten years or so it worked flawlessly. At one point though I bega
n to notice that For some time the channel on the far right side, (looking  
at the front of the unit) was lower than the rest. At some point it quit co
mpletely and I just used it on two channels.  

Last year I got the chance to pick up one of these receivers for parts. I c
leaned mine all up and swapped the two four channel boards from the organ d
onor into mine. I bench tested it for weeks before returning it to the cabi
net.The unit worked great for three days after which I once again lost that
 fourth channel.  

I hate to shotgun repairs but this is a very difficult receiver to service  
because boards were built one on top of another. In other places switch ban
ks are obstructed by component placement and you have to disassemble a lot  
of stuff to get at what you're after. In short when it's working it's great
 but just hope and pray that you'll never have to service it. It's your bas
ic nightmare.  

Over time, I worked on this fourth channel problem, John Del who is one of  
the finest technicians I know worked on it and I even had it to a repair ce
nter outside of Boston. None of us had any luck. So not wanting to haul thi
s 85 pound monster back down to the shop once again I just resigned myself  
to just using it as a two channel receiver.  

Then last night something happened that piqued my interest and changed my m
ind. We were watching a TV show on the lap top. The computer's headphone ja
ck was plugged into a line input on the receiver. For whatever reason the p
rogram audio was very low so we had the receiver volume level cranked up. A
fter the program ended my wife unplugged the 3.5mm plug from the computer w
ithout first dropping the receiver audio level. The sound was something you
 don't ever want to hear. I thought that I had just lost three working chan
nels as well as the speakers.  

But to my relief everything seemed OK. And in fact after the "event" the pr
eviously non working fourth channel was once again working perfectly. So fo
r a brief time I sat back and enjoyed some four channel music as it should  
sound. I shut it off last night and this morning I wasn't surprised to find
 that the channel was out again.  

I seem to remember working on some of the receivers of the day back in the  
mid 70's and I recall that we had problems with flaky FET's. The receiver w
ould start crackling and touching a hot soldering iron to the bad FET would
 either fix the problem or make it worse. Of course whatever component it m
ay be because of the way it was built, finding the bad one in this receiver
 could be next to impossible.  

There was gentleman who I spoke with in the past on this forum about this r
eceiver. It seems that he used to work on them and he was a wealth of infor
mation. His name was chuck but I don't have his email address. Does anyone  
know how to get in touch with him? In any event if anyone has any insight o
n this problem I would sincerely appreciate your input. Thanks, Lenny

Re: Sansui QRX 5500 quadrophonic receiver one channel is out but then an accident brought it back, (for a breif time)
Believe it or not, this is a common failure.  The protection relays get a b
it of corrosion on them and don't pass the signal along.  You can try clean
ing the contacts or just replace the relays.  The increased signal level of
 the higher volume can sometimes "span the gap" and appear to work OK.

Dan

Re: Sansui QRX 5500 quadrophonic receiver one channel is out but then an accident brought it back, (for a breif time)
On 08/11/2019 00:19, abrsvc wrote:
Quoted text here. Click to load it

Or mechanical stress on the circuit board jolts the contacts.

--  
Adrian C

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