I have an SX-1010 that I just opened up and nuked all the controls with DEOX-IT.It plays great for perhaps 60 seconds and then develops a popping and cracking in the right channel.This noise is not effected by the volume control and remains with the volume control at zero. Anybody want to lead me in the right direction?Thanks.

Is the side that's crackling getting hotter than the other side?
Does it do it in all modes?
Check the various selector switches, aux phono etc. while it's making the noise to see if they have any effect.

Oh well.This time it played great for about 5 minutes,lost the left channel,right channel got noisy,and then it went in to protection.Only thing hot is the heat sink on the power supply board.I am leaving for the weekend and will play with it some more Sunday afternoon.Probably going to be above my pay grade.

I turned it on again.As soon as it cools down it comes back on and plays fine for a few minutes.Something is obviouly breaking down when it gets hot.I just have to find it.

Have you checked the DC offset, could be protect circuit, or the bias adjustment?. It could be a number of things. It dosent make sense that it gets so warm in 30 secs. or even 5 mins. Does that model have the preout, main in jumpers, If you have, or could borrow, another preamp, poweramp, or integrated you should be able to determine wheather it is the power amp, or the prelamp by feeding (with interconnects) a good known preamp source into the questionable power amp , or feeding the questionable preamp out to another good known power amp. By process of elimination At least you should be able to determine where the problem lies. Good Luck. CC

Charlie, it IS the power amp, although it DOES have pre-out / power amp in jumpers that can be pulled, but if it goes into protect, it's the amp.

If you have a DVM, we can check the power supply voltages first, then proceed with blasts of freeze spray.

It will probably be some small transistors, driving th ebig boys nuts, the fault is probably pushing the bias way up.

OK.The power supply voltages are all within a couple of percent.The DC offset is great,5 mV on one about 10 mV on the other.When it starts acting up I can cool the heat sink that has the bias control stuff on it and it comes back.I checked the bias with a set of speakers since I don't have any 8 ohm resisters here and it is only about 25 mV on both channels.Supposed to be 50.Can I set it using speakers instaed of 8 ohm resisters?Why would they both be low?Would very low bias make the power transistors quit amplifying and shut it down?

Actually, the popping issue is likely unrelated to the bias.

I still don't see where you've isolated the issueto determine if it is originating from the preamp or the amp. The 'protection' issue may be a fault with the protection circuitry, and unrelated to the popping.

Pull the jumpers that connect the preamp to the amp, and listen for the popping. If it is gone, then it's a problem in the preamp, else it is an amp problem. My guess is that the preamp is the problem...the amp section on the 1010 is pretty bulletproof. But don't guess here - find out for yourself.

The protection board needs new caps and possibly a few new transistors to make it a reliable part of the receiver (very common deal).

The problem has evolved since the initial post.I think the popping in the right channel and the left channel dropping out are two different issues.The popping has not repeated.The left channel dropping out is reliable and freezing the C1448 will bring it back.Could be that is not the culprit ,but something on that heat sink being cooled brings it back.Maybe when I correct that it will play long enough for the popping in the right channel to come back if they are not related.

Well,I went back to set the bias and the left channel kept creeping up.Somewhere over 100 mV it dropped back to nothing and the channel dropped out.I sprayed the heat sink with some freon and it came back and I tried to adjust it and finally got it to stabilize at 50mV.It's been playing for about an hour.It's possible that the bias trimmer was dirty.

Good news bad news.Apparently the bias problem was just a dirty trimmer pot.But,the bias was what was shutting it down.Now my popping noise is back.Very intermittent,maybe once an hour,but quite loud.I may just wait and see if it gets worse.Hope it doesn't fry a speaker.Otherwise,it's a great sounding receiver.Every light works,and it doesn't appear anybody has been messing around in it.I am going to take it to the lake and aggravate my neighbors.

Pull the jumpers that connect the preamp to the amp, and listen for the popping. If it is gone, then it's a problem in the preamp, else it is an amp problem. My guess is that the preamp is the problem...the amp section on the 1010 is pretty bulletproof. But don't guess here - find out for yourself....

That problem sounds alot like my SX-1250. Tarior finally got it back to working condition, but it took a couple of trips under the knife to do it. A nice unit like a SX-1010 deserves to be working properly. It's not worth popping a good set of speakers over. Fixing the receiver first will save you in the long run. I popped a speaker cabinet once on a borderline receiver. It was exspensive to replace the parts and a pain in the butt to track them down. :yes: Brad

The popping noise has not recurred.But,the bias on the left channel kept dropping to zero and finally a 2.2k resistor in series with the trimmer resistor smoked.I replaced the 2SC1448 bias transistor thinking it was shorted.But it was not the problem.As soon as I turned it on the resistor started smoking again.Maybe the trimmer resistor shorted.Doesn't seem like it would cause enough current to be moving to burn up a reisistor,1/4 watt or not.I am way over my head.Anybody know a replacement for that ACP 040-0.Or,is it a waste of time?

There are TWO 2.2k resistors, and both should have only +/- 1.8 V on them on the trimmer/bias side, if that 2.2k is smoking, it's got a LOT more voltage across it, like if the bias trimmer VR1 (470 ohms) has opened up, then the trimmer will also have more than +1.8 on it's connection to the 2sb528's collector, probably more like 50 volts.

But much more could be wrong on the other side of the 2.2k, because that much current is allowed to flow, either the 2sd358 is shorted, the 2sc945 could be working correctly OR it could be shorted.

Looking at the 2sc945 circuit, the base is connected to the emitters of the output transistors, so that IF the emitters get over (0.6v x one over the R37 (2.7k) and R39 (1.2k) voltage divider = 1.95v) 1.95v volts (with 0.6 ohm emitter resistors that means there is 3.25 amps of output current), it will be a fault condition, the 2sc945 is turned ON, and the collector to emitter current of the 2sc945 is switched on hard, shorting the base drive to the output, thus shutting down the bias drive to that section, and PERHAPS that 2.2k 1/4 resistor is INTENDED to blow, to protect the outputs.

Thus the bias fault could be blowing up the 2.2k resistor (intentionally!??), to protect the outputs. Correct the bias fault, replace the 2.2k and you could be ok.


Check the voltages as per the schematic, I expect you still have bias trimmer problems, or bias problems in general. Quite frankly, the bias section can be the most destructive during a fault, and I would replace flakey trimmers.

Now I see what EchoWars MIGHT have ment when he said "the amp section on the 1010 is pretty bulletproof".

edit: ahhhh acp-040... I understand...... bourns trimpots.... 470 ohms..... specific footprint..... looking......

That bias trim pot has a little over 23 volts on it now!

That's waaayyyyy bad....

THe green line is the bias current circuit, with the voltages shown, the red circled 1.8v readings are the most important.

You read the power supply circuits, this shouldn't be much of a stretch.

The red line around the pot represents a bypass short around the pot, do this to see if the voltage returns to about 1.8v. If so, the pot is at fault.

If not, check the stv-3h diodes, CAREFUL, THE LEADS ON THESE ARE FRAGILE, especially at the component case. When you find the component with a huge voltage differential across it (usually jumping from a positive to a negative voltage ) that should be your culprit. The two transistors should be the components with 50 volts across them.

http://www.audiokarma.org/forums/attachment.php?attachmentid=54672&stc=1&d=1184625722

Mark,let me ask you this.I know the 2SB528 has 56 volts on one side and -25 on the other when it should be +1.8.The trimmer measures the same resistance as the working one on the other channel, so I think I was chasing a squirrly transistor with it the whole time and the trimmer is probably OK.It couldn't have that much effect on the voltage anyway.I have to drive 100 miles round trip to get electronic parts.So,I might as well change every transistor on that board that could be the problem.R23 is the reisistor that is cooking.The voltage on everything is negative,so I guess it's coming from the 2SC1451 side.Anyhow,I need to change any transistor that could be doing this.Are these the only two?

There are alternatives to driving a lot, especially if you are in the U.S. and you have a bit of patience.

Digikey.com has a $5 small order charge for under $25 IIRC...
mouser.com has no minimun order, and on small orders they will if asked ship the order first class mail, usually costing less than 3 bucks for shipping.

I do it all the time.

The trick to testing the transistors is to either look for emitter to base voltages at about 0.6 volts, or to remove the thing and do the 6 way dmm diode test.

This thread: http://www.audiokarma.org/forums/showthread.php?t=43186 explains.
this post explicity breaks out the 6 way tests: http://www.audiokarma.org/forums/showpost.php?p=835508&postcount=59
this diagram also illustrates the 8 way tests: http://www.audiokarma.org/forums/attachment.php?attachmentid=29556&d=1162593500

Mark,let me ask you this.I know the 2SB528 has 56 volts on one side and -25 on the other when it should be +1.8.The trimmer measures the same resistance as the working one on the other channel, so I think I was chasing a squirrly transistor with it the whole time and the trimmer is probably OK.It couldn't have that much effect on the voltage anyway.I have to drive 100 miles round trip to get electronic parts.So,I might as well change every transistor on that board that could be the problem.R23 is the reisistor that is cooking.The voltage on everything is negative,so I guess it's coming from the 2SC1451 side.Anyhow,I need to change any transistor that could be doing this.Are these the only two?


It's the positive side that's not drawing (enough) current, to PULL the negative voltage up.

emitter to base voltage (~0.6v), that's the key.