Sansui QRX 5500 quadrophonic receiver one channel is out but then an accident brought it back, (for a breif time)

[captainvi...@gmail.com]

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 began 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 completely and I just used it on two channels.

Last year I got the chance to pick up one of these receivers for parts. I cleaned mine all up and swapped the two four channel boards from the organ donor into mine. I bench tested it for weeks before returning it to the cabinet.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 banks 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 basic 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 center outside of Boston. None of us had any luck. So not wanting to haul this 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 mind. We were watching a TV show on the lap top. The computer's headphone jack was plugged into a line input on the receiver. For whatever reason the program audio was very low so we had the receiver volume level cranked up. After the program ended my wife unplugged the 3.5mm plug from the computer without 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 channels as well as the speakers.

But to my relief everything seemed OK. And in fact after the "event" the previously non working fourth channel was once again working perfectly. So for 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 would 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 may 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 receiver. It seems that he used to work on them and he was a wealth of information. 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 on this problem I would sincerely appreciate your input. Thanks, Lenny

[abrsvc]

Believe it or not, this is a common failure. The protection relays get a bit of corrosion on them and don't pass the signal along. You can try cleaning 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

[Trevor Wilson]

**Output relays. Replace 'em or clean em. Very common in 40 ~ 50 year
old equipment. In fact, I have a Sansui AU919 with precisely that problem.

--
Trevor Wilson
www.rageaudio.com.au

[Phil Allison]

Trevor Wilson wrote:

-----------------------

>
> **Output relays. Replace 'em or clean em. Very common in 40 ~ 50 year
> old equipment. In fact, I have a Sansui AU919 with precisely that problem.
>
>

** Certainly true.

I can spend hours on an old Jap receiver, from one of the major brands before it is all working again.

Corroded toggle, pushbutton and rotary switches, pots, RC sockets, multi-pin connectors, wire wrap joints, fuse clips, bulb sockets, noisy tuning gang bearings, bad headphone jacks, dead back lights and maybe a few leaky or open electros. Plus of course speaker relays.

Almost nothing in parts, but heaps of time that must be paid for.



..... Phil

[Trevor Wilson]

**My AU919 customer was real lucky. He bought it from a US seller on
eBay. It arrived in it's original packing box. When I pulled it out, I
realised that it had seen very little use, based on how much dust was
inside and the cosmetic condition of the knobs and switches. It's
probably the best one I've ever seen. Replacing the deadly 'black flag'
caps with silvered mica (at the customer's request) and ceramics, two
new relays (I could have cleaned them, but what the Hell, they were only
9 Bucks each from RS) and the job is done.

However, next week, I face off with this beast:

https://classicreceivers.com/marantz-4400
https://www.hifiengine.com/manual_library/marantz/4400.shtml

Built to be easily repaired in case of an output stage fault (which
hardly ever happens).

One of my all-time favourites. I repaired quite a few back in my Marantz
days. Nicely built, but crowded. Replacing the lamps is a nightmare. The
CRO doesn't work, but I am hopeful it's a power supply issue. A full set
of electros, lamps and all the other stuff will take me the best part of
all week to sort out. Worth it though. Arguably, the best, most
desirable 4 channel receiver ever made.

Gotta love those hipsters. :-)

--
Trevor Wilson
www.rageaudio.com.au

[Adrian Caspersz]

On 08/11/2019 00:19, abrsvc wrote:
> Believe it or not, this is a common failure. The protection relays get a bit of corrosion on them and don't pass the signal along. You can try cleaning 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.

Or mechanical stress on the circuit board jolts the contacts.

--
Adrian C