sx-550 with a hum issue

pqrannes

pqrannes

Tubes warm your heart too
I could help myself picking up a nice looking sx-550 receiver at the scouts' weekly garage sale (at 4 usd). It is an American 110v version but my huge 220v-->110v converter take cares of that part.

But the sx-550 has a strange hum. The thing is that it has a hum that is unconnected to the volumen button (doesn't turn up with the volumen) but go away when ever the sx-550 gets a clear signal either from the build in FM radio or via the aux input.

To my experience it is not the 220v-->100v giving my trouble.

Any clues?

Peter
 
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First download the sx-550 service mannual from the AK database. It is in tricomp's section and is about 9.7 meg.

Then check the ac voltages across the two big filter capacitors, and the DC regulated voltages being output from the power supply. Also do an ac voltage reading of the dc power supply's output voltage, which should be very low.

When testing for hum, only the power and speakers should be connected, eliminating any chance of ground loops.
 
markthefixer said:
First download the sx-550 service mannual from the AK database. It is in tricomp's section and is about 9.7 meg.

Then check the ac voltages across the two big filter capacitors, and the DC regulated voltages being output from the power supply. Also do an ac voltage reading of the dc power supply's output voltage, which should be very low.

When testing for hum, only the power and speakers should be connected, eliminating any chance of ground loops.
Click to expand...

thx markthefixer,

It seems the way to go. I couldn't get the access to the pioneer database to work though.

What is strange about this hum is that it goes away as soon as the receiver gets music to play either via aux input or via the tuner part: the hum is there when the tuner is between stations but disapperes when there is music - it is not that the hum can't be heard for the music it just goes away- Strange!


Peter
 
pqrannes said:
What is strange about this hum is that it goes away as soon as the receiver gets music to play either via aux input or via the tuner part: the hum is there when the tuner is between stations but disapperes when there is music - it is not that the hum can't be heard for the music it just goes away- Strange!
Peter
Click to expand...

The hum is there when switched to aux input? and if you change the TUNER it disappears?
Or the hum is there until a signal is fed into the AUX, WITHOUT touching the tuning?
Is the hum there in AM???
Is the hum there in PHONO?? (even without a phono cartridge OR cables connected?)

If you have another receiver, in aux, fm, phono and am, run the TAPE MONitor outputs into the other receiver and check for the hum.
 
I'll be combining two 550s to make one real soon. If there's any parts you may need, if I'm not using them, you can have them.

Dunno what it would be to ship to you, however.

But keep it in mind and pm me if interested- I'll make a note of it (otherwise I'll forget).
 
thx again,

The hum must be tuner related.

It is there when the tuner is not tuned precisely to a station.

But it is there whether the receiver is set to radio, aux or tape (haven't check phono yet).

If you turn the dial of the tuner away from a station while listening to something through the aux or the tape the hum comes back.

The hum doesn't come and go when you use the (tuner) muting selecter.

Some tuner part most be causing this.

Thx thedelihaus for the kind offer of parts. We'll see to that.


Peter
 
I have been researching this problem, it is very strange.

I would suspect some sort of small electrolytic capacitor used in the tuner circuits to be bad. A small capacitor that would be used for bypassing noise generated inside of the tuner circuits.

But it could also be a bad circuit board ground.

I would check each and every solder joint carefully, with a magnifying lens and a sharp pointed tool (with the power off!!) to see if the component lead is loose because the solder joint has fractured.

But after that, much more sophisticated equipment would be needed to track it down.
 
If you want, I'll have a parts unit after all. yours, just send me the cost of shipping, and your address.

Only catch, is I'll need to know this week. sorry for the short window of time.

I'll also dissassemble whatever you need and just send that. If it's small and cheap enough, I'll take care of the shipping, gratis.
 
thedelihaus said:
If you want, I'll have a parts unit after all. yours, just send me the cost of shipping, and your address.

Only catch, is I'll need to know this week. sorry for the short window of time.

I'll also dissassemble whatever you need and just send that. If it's small and cheap enough, I'll take care of the shipping, gratis.
Click to expand...

Thx thedelihaus for the kind offer. The little pioneer is nice but is only one of many receivers in my stack, so I won't go to the end of the world to make it working. I might pass it on to someone with more technical skill than me.

:tresbon: thx markthefixer for putting your efford in to the issue. It is indeed strange.

Peter, Denmark
 
I realize now that I never told the ending of this story.

The Pioneer receiver still had it's 110V power plug, but it turned out that it never the less was set for 220V! As soon as it was fed with 220V it played like baby. The strange hum issues were gone like ... clouds on a sunny day!

The receiver has now found a new (and better) home.

PQR
 
I hope it didn't you almost 2 years to figure it out! :D

Glad to hear that it's working correctly and it's getting used.
 
MAXZ28 said:
I hope it didn't you almost 2 years to figure it out! :D

Glad to hear that it's working correctly and it's getting used.
Click to expand...

No, I did figure it out a while back. But 2 years with vintage audio is like a split second, itsn't it?

PQR
 
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