sx 1050 pops on start up

Hi,

I've got a 1050 that pops and crackles loudly when first turned on. The racket gradually diminishes and within five minutes goes away and the unit sounds fine and will play all day with no trouble. Next morning when it's turned on again, will produce more popping. If left off for two weeks or more, will produce much popping. It's in both channels. Any ideas as to what causes this?

aged or failing capacitors

It's in both channels. Any ideas as to what causes this?

Click to expand...

Both channels - Power supply caps or regulator circuit (transistors).Would be the first place to start look'n...

Check the solder joints on the power supply. The amp only runs off the +/- 60v supplies, and GUESS which transistors run hottest... hot enough to crystallize the solder joint, and then it cracks at the weak point. When it heats back up after being turned on, it expands back to making good contact.

Pay attention to the solder joints on leads that come from transistors on heat sinks in the power supply.

I'm surprised that the protection isn't kicking in and out.

NOW if it were just ONE channel..... :scratch2:

1050 pops

I finally got around to opening up the 1050. I examined the power supply with a good light and found nothing out of the ordinary. Took a reading on a transistor, and when it was supposed to be open, I got a number, which only means it has to be unsoldered to be tested. If I'm going to unsolder something, I might as well replace it while I'm at it. I got the list Mark put together and will get new transistors and caps, then we'll see if that does something for the popping.

While I was in there I noticed that one of the big 22,000 uf caps is starting to leak a little. Could this cause a pop?

Thanks, everyone, for the input.

mesure the dc voltages of the caps, and then the AC voltages. BOTH readings are to be taken across the capacitor terminals.

Some cheap meters will need a 0.1uff cap in series with the test leads to block the DC voltage so we only read the ac voltage. The cap's voltage rating must (of course) be greater than the power supply voltage.

post the dc and ac voltages for the caps, and we will compare them.

1050 caps

I got 62.2 DC on each cap and 138.1 ac. If I switch leads on ac I get zero. If I switch leads on dc only the polarity changes.

steamwhistle said:

I got 62.2 DC on each cap and 138.1 ac. If I switch leads on ac I get zero. If I switch leads on dc only the polarity changes.

Click to expand...

While the dc voltages look good, you need the capacitor in series with the test leads to get the correct ac readings.

The ac readings will be a better indicator.

1050 pops

I didn't have a cap to hook up to the dmm so I ordered one from Mouser along with the other parts. An old Radio Shack meter gave me an AC reading of 1.098, but I'm not sure if that means anything.

steamwhistle said:

I didn't have a cap to hook up to the dmm so I ordered one from Mouser along with the other parts. An old Radio Shack meter gave me an AC reading of 1.098, but I'm not sure if that means anything.

Click to expand...

The ac readings have to be compared capacitor to capacitor. We are looking for an imbalance.

1050 pop

I took the readings off both caps and they were the same. This morning I re read them, waiting ten seconds for the readings to stabilize, and they were both 1.072 v ac.

1050 pop

My mouser shipment already came in. I hooked up a .1 cap to the positive lead on my dmm and got a reading of 36.2 mv ac on the leaking 22,000uf cap and 33.6 mv on the other. Does this mean anythinig?

steamwhistle said:

My mouser shipment already came in. I hooked up a .1 cap to the positive lead on my dmm and got a reading of 36.2 mv ac on the leaking 22,000uf cap and 33.6 mv on the other. Does this mean anythinig?

Click to expand...

No significant imbalance seems to exist. Those are the correct numbers - at least in the ballpark. So the power supply isn't lopsided...:scratch2:

1050 pops

All right. I'll go ahead and recap and put in new transistors on the power amp and fire her up--see what happens. Hopefully I'll post the dancing banana next message.

1050 pop

I put in all new caps in the power supply and the unit powered up and played with no pops or crackling. So then I put in q4 and powered up again. The unit sounded good. Then I put in q3 and all sound stopped. I made sure to get the right legs in the right holes, ecb instead of bce. I tested the old q3 and it was okay so I reinstalled it. Still no sound. When I flip the tone lever, there is a big pop and protection goes on for three or four seconds. No dancing banana for me! Any hints at what happened?

Several things:

one, post the parts list you are working from
two, read and post the voltages on pins 16 & 15
three, turn it off and wait. the voltage on pin 15 should be about half of pin 16's 60 volts.

if q3 went in bad or something, q1, q2, q3 & D1(especially) are now all suspect.

it's hard to say what went wrong, nobody was watching or filming what was done.. it's all water under the bridge now anyways......

1050 pops

Here she goes:
here's an update of an old post, with all the parts to do an entire rebuild, prices are probably a bit off, it's old:

sx-1050 power supply
q1 2sd313 to-220 bce npn 60v 3a 30w 5mhz
replacement part # 512-ksc2073tu_q @ $0.53 ea (bce, same layout) 150v 1.5a 25w 4mhz
q2, q3 2sc869 to-92 bce npn 50v 30mA .2w 150mhz
replacement part # 512-KSC2310YBU @ $0.11 ea (ecb, opposite layout) 150v .05a 0.8w 100mhz
q4 2sc1318 to-92 ecb npn 50v .5a .6w 200mhz
replacement part # 512-KSC2690AYSTU to-126 (ecb to ecb, same layout, different case) 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
q5 2sb507 to-220 bce pnp 60v 3a 30w 5mhz
replacement part # 512-KSA940TU_Q @ $0.54 ea (bce, same layout) 150v 1.5a 25w 4mhz
q6,q7 2sa628 to-92 ??? pnp 25v .1a .15w 100mhz
replacement part # 512-ksa733clta @ $0.05 ea (ebc layout) 50v .150a .250w 180mhz
q8 2sa720 to-92 ecb pnp 60v .5a .625w 200mhz
replacement part # 512-KSA1220AYS to-126 (ecb to ecb, same layout, different case) 120/a160 1.2a 20w 155mhz 35-320hfe $0.39
q9,q12 2sd325 to-220 bce npn 35v 3a 10w 8mhz
replacement part # 512-ksc2073tu_q @ $0.53 ea (bce, same layout) 150v 1.5a 25w 4mhz
q10,q11,q13 2sc945 to-92 ecb npn 50v .1A .25w 150mhz
replacement part # 512-ksc945clta @ $0.06 ea (ecb to ebc, different layout) 50v .150a .250w 180mhz

d1 wz-140 mouser.com part # 512-1n5244b @ $0.04 ea
d2 wz-130 mouser.com part # 512-1n5243b @ $0.04 ea
d3,d4 wz-140 mouser.com part # 512-1n5234b @ $0.04 ea

c1,c9 220uF 80v mouser.com part # 647-UHE2A221MHD 220uf/100v $1.48ea
c3,c12 47uF 16v mouser.com part # 647-UPW1E470MDD 47uf/25v $0.31ea
c6,c14 47uF 35v mouser.com part # 647-UPW1H470MED 47uf/50v $0.34ea
c7 10uF 35v mouser.com part # 647-UPW1H100MDD 10uf/50v $0.25ea
c8 1uF 50v mouser.com part # 647-upw1h010mdd 1uf/50v $0.23ea
c15 100uF 35v mouser.com part # 647-UPW1H101MPD 100uf/50v $0.50ea
c16 220uF 25v mouser.com part # 647-UPW1V221MPD 220uf/35v $0.56ea
c17 47uF 10v mouser.com part # 647-UPW1E470MDD 47uf/25v $0.31ea
c20 100uF 25v mouser.com part # 647-UPW1V101MPD 100uf/35v $0.15ea
c22 47uF 10v mouser.com part # 647-UPW1E470MDD 47uf/25v $0.31ea
c23 2.2uF 50v mouser.com part # 647-UPW1H2R2MDD 2.2uf/50v $0.23ea
c24 220uF 16v mouser.com part # 647-UPW1V221MPD 220uf/35v $0.56ea

Sharp eyes will notice that Q4 and Q8 have been substituted with transistors with different, larger cases. They can handle more power, and will not be straining even under reasonable overload conditions. They also have small enough leads that they will fit through the current holes. A final bonus is that there are no metal tabs exposed to short out accidentally, any heat sinks will not be electrically live, but will most likely NOT be needed on Q4 or Q8.

Also the voltage ranges of the electrolytic capacitors has been increased, most specified caps now have a 50 volt rating. The difference is just a few pennies at most and are better suited to survival under fault conditions as well.

mouser.com EZ buy BOM import tool data:
647-UHE2A221MHD
647-UPW1E470MDD
647-UPW1H470MED
647-UPW1H100MDD
647-upw1h010mdd
647-UPW1H101MPD
647-UPW1V221MPD
647-UPW1E470MDD
647-UPW1V101MPD
647-UPW1E470MDD
647-UPW1H2R2MDD
647-UPW1V221MPD
512-ksc2073tu_q
512-ksc2310YBU
512-ksc2310YBU
512-KSC2690AYSTU
512-KSA940TU_Q
512-ksa733clta
512-ksa733clta
512-KSA1220AYS
512-ksc2073tu_q
512-ksc2073tu_q
512-ksc945clta
512-ksc945clta
512-ksc945clta
512-1n5244b
512-1n5243b
512-1n5234b
512-1n5234b
__________________
voltage on 16 was 64.6
voltage on 15 was -2.16
turned off, when 16 dropped to 0, 15 read -13mv

I checked for shorts along the foil side of 15's track and found nothing. No bridging at solder points.

The trouble started when q3 went in. I used heat sinks on q3's legs while soldering. I did not shield a little 1000pf ceramic cap which shares a solder joint with q3.

well, this is interesting...

the pin 16 voltage of 64v is a bit high, but we don't know what it was originally since you never posted any "before" troubleshooting readings I am aware of.

the pin 15 voltage of -2v means Q4 is either destroyed, or it's base (or even the collector) is shorted to ground, and Q4 supplies most of the signal electronics, so no sound.

So first take and post readings from Q4's collector, base and emitter to see what it is being told to do by the circuit.

Then take and post readings of Q1's collector, base and emitter, as well as pin 2.

1050 pops

Pin 2 = 78 volts. Few other pin readings make sense because the unit is in protection mode.

Q1

Pos to base, Neg to emitter =.584 v
Pos to base, Neg to collector = .581v
Neg to base, Pos to emitter = 1.054v
Neg to base, Pos to collector = .595v
Neg to emitter, Pos to collector = 1.002v

Q4 readings as above

.571
.567
climbs to 1.1 v, then opens
.898
.581

steamwhistle said:

Pin 2 = 78 volts. Few other pin readings make sense because the unit is in protection mode.

Q1

Pos to base, Neg to emitter =.584 v
Pos to base, Neg to collector = .581v
Neg to base, Pos to emitter = 1.054v
Neg to base, Pos to collector = .595v
Neg to emitter, Pos to collector = 1.002v

Q4 readings as above

.571
.567
climbs to 1.1 v, then opens
.898
.581

Click to expand...

sorry, my bad for not being explicit, the requested readings are voltage measurements made referenced to the chassis ground.
We have to sort out the power supply before moving on to the protection.

pin 2 says that the circuit is being fed properly.

This:

voltage on 16 was 64.6
voltage on 15 was -2.16
turned off, when 16 dropped to 0, 15 read -13mv

I checked for shorts along the foil side of 15's track and found nothing. No bridging at solder points.

The trouble started when q3 went in. I used heat sinks on q3's legs while soldering. I did not shield a little 1000pf ceramic cap which shares a solder joint with q3.

Click to expand...

is the trouble point we are at