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do you have buzzing too? Pioneer SX 990 / SX 2500 ..??

now I know that the buzzing comes from the RCA Pre Out connectors.

I tried to connect another device to the Pre Out SX 2500 and the same hum was heard in the another device.

The Elko cap are new, so it is possible that some transistor does it, or...
 
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Sorry I did not realize the clip was there... da. Sounds to me like a power supply problem. I noticed, looks like your amp was rebuilt. I wonder if any work was done to the power supply and I don't mean the supply for the power amp. The lower voltage supply, I don't have a schematic. If you have another amp you could take the MAIN OUT to another amp (Aux or Tape in) if you get the noise then most likely from the low voltage supply. It is difficult to tell exactly without being there. Hope this helps.
 
JRC75 said:
Sorry I did not realize the clip was there... da. Sounds to me like a power supply problem. I noticed, looks like your amp was rebuilt. I wonder if any work was done to the power supply and I don't mean the supply for the power amp. The lower voltage supply, I don't have a schematic. If you have another amp you could take the MAIN OUT to another amp (Aux or Tape in) if you get the noise then most likely from the low voltage supply. It is difficult to tell exactly without being there. Hope this helps.
Click to expand...
Yes,I just wrote it for you that I connected the Pre Out output and connected it to another amplifier, and the same buzz was heard there as well.
now I replaced the original Q3 and Q5 2SC870 transistors with new KSC1845FTA ones.

Measurement from the power board to the ground.
Q1 2SC1061
B 12,860V
C 19,485V
E 12,335V
//////////////////////
Q2 2SC971
B 0,651V
C 4,655V
E 0V
///////////////////////
Q3 NEW 1845
B 1,203V
C 4,670V
E 0,654V
///////////////////////
Q4 2SC1061
B 14,165V
C 21,340V
E 13,584V
/////////////////////////
Q5 NEW 1845
B 14,770V
C 21,350V
E 14,210V
/////////////////////////
Q6 2SC627
B 85,29V
C 88,87V
E 84,75V
/////////////////////////
Q7 2SC485
B 40,493V
C 71,23V
E 39,985V
////////////////////////
Q8 2SC968
B 14,142V
C 40,460V
E 13,590V

============================
voltage outputs from the power board
B1 21,878V
B2 -5,05V
B3 12,423V
B4 13,662V
B5 26,436V
B6 84,78V
B7 89V
B8 39,987V

contact N.7 84,96V
contact N.8 21,735 V
 

Attachments

  • SX2500 PS.jpg
    SX2500 PS.jpg
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The DC voltages may be OK, but there could be AC ripple if you do not have an oscilloscope, you could try measuring with an AC multimeter. Also look at all the ground connections (do this first). You could also replace the electrolytics on the PS board, are they original?
 
JRC75 said:
The DC voltages may be OK, but there could be AC ripple if you do not have an oscilloscope, you could try measuring with an AC multimeter. Also look at all the ground connections (do this first). You could also replace the electrolytics on the PS board, are they original?
Click to expand...
yes, I checked the grounding and the electrolytic capacitors are new.
.Do you mean AC on the rectifier diodes?or which AC voltage?
 
The PS voltage out could have an AC componet on the DC which AC should not be there. I watched a Tube video where a guy used a signal tracer to find a bad componet in the power supply. Can't remember which one. This PS I think it was a zener generating the noise, been a long time ago. Try looking up ripple on power supplies.
 
I replaced all functional original Q with brand new ones, and nothing improved.
Q1 2SC1061 -> KSC2334
Q2 2SC971 -> KSC2690
Q3 2SC870 -> KSC1845
Q4 2SC1061 -> KSC2334
Q5 2SC870 -> KSC1845
Q6 2SC627 -> KSC3503
Q7 2SC485 -> KSC2690
Q8 2SC968 -> KSC2383


Please is there an owner of such a Pioneer SX 2500 and there is no buzzing, humming, noise in the speakers at minimum volume, or no volume?
 
Yes, I have an sx-2500. It's original as far as I can tell. I didn't even clean the pots.
With volume set to minimum I can still hear sound and hum (60 or 120hz, can't tell the difference, not just yet)
On power up it has a massive thump and that's why it's not in use.
With all the above problems it still sounds wonderfull and I hope to restore it one day.
 
Thank you for your information.
yes, even without a relay, these devices make a real boom in the speaker when turned on, but their sound is awfully good At least I like it very much.
maybe it would help a little to clean the main switch, but probably the best solution is a soft start relay.
I cleaned the power switch but it didn't help when it turned on.

If this device can be used without such intense hum in the speakers, the best solution is to look for the problem with an oscilloscope.

But maybe they are the owners of such a device, which is without interference, and they know how to advise and facilitate the repair, by publishing information, and also help other users of this or similar device.
 
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Have the same issue and actually starting to clean this sx2500 up. Ironed out a lot of issues. Next will be the faint buzz. Anyone come across a fix?
 
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