Help with crackling/popping Sansui QRX 5500

[Ziegert123]

Hello,

I am new to AK and by no means an audio expert so I would greatly appreciate any input I can get. I have a Sansui QRX 5500 from the mid '70s that has been experiencing some issues. The unit worked perfectly fine for a year, then I moved to a new house and had to re-attach all my speakers and turntable. After hooking everything up again I would turn the unit on and there would be loud crackling coming from one speaker. After disconnecting that speaker the crackling would move to another speaker, but seemed to occur only with a few of the speaker channels. The crackling was present despite the speakers receiving no audio signal. In other words, the second I powered up the Sansui I would hear crackling (also no crackling when headphones were used). I've tried swapping out the affected speaker with another speaker. No change. I've tried changing out all my speaker wire with new, high quality wire. No change. And I have opened up the Sansui and cleaned all the pots and switches and such with Deoxit. But the crackling still persists. Can anyone help me out with this situation? I am getting quite frustrated at this point...

 

[cademan]

This may be beyond your capabilities but in my experience, it sounds like it could be a driver transistor in that specific channel. When they begin to crap out, they produce static in the channel they are driving.

Isn't the QRX a quad receiver? Four channels and only one is showing signs of being problematic.

 

[Ziegert123]

Thanks for the quick reply! Yes the QRX is a quad receiver and I'm only experiencing problems with one or two channels. Looks like I'll have to take her in to get fixed up. Thanks for your help!

 

[Shadz]

Hello,

I am having the same problem with my QRX-4500. Crackling on the front right speaker even when the volume knob is down.
Where you able to get yours fixed ?
Do you know which parts were replaced ?

Thanks !

 

[teal'c]

Hello,

I am having the same problem with my QRX-4500. Crackling on the front right speaker even when the volume knob is down.
Where you able to get yours fixed ?
Do you know which parts were replaced ?

Thanks !

Ziegert123 was last seen:
Jan 15, 2017

 

[blhagstrom]

Hey Shadz,

Where are you?

I just rebuilt a QRX-5500 for a customer.
It’s not cheap but after you hear it, you forget about the cost.

 

[teal'c]

Hey Shadz,

Where are you?

I just rebuilt a QRX-5500 for a customer.
It’s not cheap but after you hear it, you forget about the cost.

Did you run into anything like this?

The earlier boards, which were in the QRX5500 and QRX7500, are even more interesting. There is a crucial electrolytic cap that makes them work (crucial value). If you just replace the caps on the board, more than likely, since electrolytics have such a wide tolerance, the crucial cap will not get replaced with the correct value cap, and the boards will no longer process at all. You can imagine how many hours it took us to figure this out, the hard way.
.

I asked him about it in the thread and through PM if he recalled which cap but it seems he wants to keep it a secret since I never got a response.

 

[blhagstrom]

The unit I worked on had issues.
At least one channel was out, maybe two.
Noisy channels.

The owner wanted a restore so all new caps throughout and a deep cleaning and she was fine.


Crackling through a speaker with no signal and volume down indicates a flacky transistor for the most part.
But, a bad capacitor does the same thing.

Does that help?

No?


Because "which" transistor or capacitor or whatever is bad is the mystery and you will not get any useful information on an internet forum that will lead you straight to a solution.

Warning: hard Fact.
It's old, it's not working right, i.e. broken. It needs repair. It's vintage electronics. It needs a qualified service person (probably has a sticker on it that says that, something like "no user serviceable parts inside").

Warning: Hard Fact
The "qualified service personal" are old, probably not working either. So, finding someone that knows how to find the bad transistor or capacitor or whatever is going to be tricky.

I can tell you something like, "Oh I'll bet it's transistor Q17, replace that and see if that fixes it", but the chances are poor that it would help.

You've said you are not an audio expert.
I am assuming you know nothing about electronics and have no tools or skills.
I may be wrong.