Pioneer sx-626 Popping Noise when turned on

You probably have some transistors with the corroded legs. Somehow, the corrosion makes it's way inside, and you get all kinds of popping.

If your 626 is anything like my 535, you can isolate the power amp board by removing the three input wires. If the popping stays, the fault is here. If it goes away, the fault is in the pre-amp stage. Try tapping on the small transistors with a plastic pen and see if you can get it to pop.

You can see my threads here.

http://www.audiokarma.org/forums/showthread.php?t=404240

http://www.audiokarma.org/forums/showthread.php?t=407623

Lee.
 
Thank you both for the suggestions. When I get some time to carefully check it out I will let you know what I found. By the sounds of it, the problem has nothing to do with the power switch, so it looks like I will get my first chance to poke around inside.

Could you lead me to a good source for replacement electronic parts?

Thanks
 
The 626 has cap coupled output's. Meaning that there is NO Protection Relay and there are TWO(2) 2A fuses for protection. The thump immediately upon power up is the coupling caps charging with DC leaking thru. The thump is the DC Voltage. This is typical for cap coupled amp's with marginal or failing caps. Look for the 2200uf/35V caps on the amplifier board(s). You can increase the value's of these to 3300uf/50V or 4700uf/50V.

Until you get the new caps, put it on a power strip. Then when you power down, turn the speaker switch to OFF, and turn off power at the strip. To power up, Switch on the power strip, count to 5 and turn the speaker switch to which ever speaker lead your's are connected to, ("A" or "B" or "C").

The manuals are @ hifiengine.com. You'll have to register, but it's free.

Mouser will have the parts.

Main Filter Cap.
UVR1J332MRD6 3300uf/63V QTY=1
http://www.mouser.com/ProductDetail...piMZZMtZ1n0r9vR22afkwEr%2bqyzvlw9tR0%2bo79c=

COUPLING CAPS
UPW1H222MHD 2200uf/50V 18mmx35.5mm QTY=2
http://www.mouser.com/ProductDetail...GAEpiMZZMtZ1n0r9vR22eD8a%2bFprAqc79oSbdIHPbo=

OR
UPW1V222MHD6 2200uf/35V 18mmx 25mm QTY=2
http://www.mouser.com/ProductDetail...GAEpiMZZMtZ1n0r9vR22eD8a%2bFprAqc8ccKvqogJ9E=

or UPW1V222MHD 2200uf/35V 16mmx31.5mm QTY=2
http://www.mouser.com/ProductDetail...GAEpiMZZMtZ1n0r9vR22eD8a%2bFprAqcC4CpvmWYBJo=

The last two are the same except for size.

for the Coupling caps on the amplifier board. I'd go with the 50V coupling caps.

This should either eliminate or greatly attenuate the thump. Again the thump is a byproduct of a cap coupled design. The speakers are connected to the amp all the time and when powered up, with marginal caps, you will get a thump, due to DC voltage getting by the cap to the speaker. When the cap is charged fully, the thump stops. That's why the recommendation of a power strip until you can recap the unit.


Larry
 
Transistor Q13 (2sc893) in the power amp is a turn on delay for the input / idle current amplifier stages. R43 (56k) and C21 (100uf) set the delay. C21 could have lost capacitance - replace it as well as recap the power supply regulators, and check that Q13 isn't shorted.
 
I know this is an old thread but did you ever reduce the speaker pop/thump on your SX-626 huck1978? I have the same model and l have replaced Q13, C21, the output coupling caps and the power supply caps, R43 measures perfectly at 5.6K. No improvement has been made, must be the nature of these. I have owned many cap coupled amps from this era with varying degrees of this symptom though to be fair.
 
I also have a thump when turning my on my SX-626. I recapped the power amp board, but I did not replace the 63v 3300uf main filter cap. Would replacing this cap help reduce the thump?
 
A thump is normal in a coupled amp. Try this: put your speakers on B output. Turn on the unit, wait few seconds then turn to speaker B. That little delay allows the main caps to charge.
 
A thump is normal in a coupled amp. Try this: put your speakers on B output. Turn on the unit, wait few seconds then turn to speaker B. That little delay allows the main caps to charge.

Thanks. I moved the speakers from A to B to C and the thump is only when the speakers are connected to B or C. There's no thump when connected to A.
 
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