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Smoking SX-1050 : (

bowtieman427

bowtieman427

Active Member
I picked up a Spare parts SX-1050. It is very nice cosmetically all it needs is tuner nob, one toggle switch nob and the AM anttena bracket is broke. So I thought I may try to get is going again. I pluged it in no problem. Turn it on...No lights, nothing comes on and it smokes. Took the covers off tried again to see where it was smoking. The smoke is pouring out the SURGE CURRENT SUPPRESSOR ASSEMBLY AWX-098 namly out of what appears to be the large coil in the back of the board.

History guy I got it from tells me he fried it while driving 4 speakers on full bore it went off and he noticed it smokeing (I geuss he likes his music really loud)
Any ideas on how to repair ?
Any ideas where to get this part if that is all it needs ?

thanks in advance
Jim
 
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Well, for starters, it sounds like your soft-start realy isn't kicking in and bypassing the surge resistor. Chances are that you have some bad outputs, too.
 
You think there are bad ouptuts, possibley a relay and that is what took out the surpresser ?
Is there a way to do some checks with power off ?
thanks Jim
 
The typical scenerio is this: Amp blows a couple of outputs, then the fuse. Use says, "Hey! It's only a popped fuse!" Use installs new fuse, unaware of blown outputs. User fires up the amp. Soft-start relay, which relies on voltage from the regulator or main caps, cannot fire to bypass the soft-start resistor, since the shorted outputs are pulling so much current that the caps (or regulator) cannot charge. All that current due to the dead transistors is routed through this forlorn soft-start resistor, which was never meant to carry the operating current of the device for more than about 1 second at power-up. Resistor burns up, and now the device does nothing at all, acting as if it has on open primary winding on the transformer. User takes unit to clueless tech (or troubleshoots it himself), and decides the transformer is bad. Amp ends up in the landfill (or sold on eBay...same difference).
 
Translated: $$$$$$$$$$$$$$$$$$

It's going to NEED a LOT of parts. And a lot of work with an experienced eye to spot problems. A high power amp like this is nothing to fool around with in any case, but when it's been mistreated like this, it's like juggling a rattlesnake.

PLus at this point, with the soft start going up in flames, the primary wiring could be melted, as well as the secondary wiring to the outputs.

Pull and test:
1. output transistors, 8 of them plus associated components and possibly wiring
2. driver transistors, 4 of them with associated components as well
3. bias transistor circuits, probably.. hopefully the four bias diodes (stv-3h) are ok, those are VERY hard to find.
4. power supply regulator transistors if you WEREN'T lucky
5. whatever primary circuit wiring was fried.

The guy who put this up as parts knew what he was doing.

It can be done. It'll be expensive, AND a PITA.

How much did you spend for it?

At what point will it be too expensive to fix?

Do you have a DMM with a diode test? Do you know how to test transistors with a DMM diode test?

It will be a LONG time before the power is turned back on.

Take a long good look at the wide pc board in the back, mounted to the heatsinks, you will be getting INTIMATELY familiar with it and everything mounted on the heatsinks.

Did you even get the service manual?
 
markthefixer said:
Translated: $$$$$$$$$$$$$$$$$$

It's going to NEED a LOT of parts. And a lot of work with an experienced eye to spot problems. A high power amp like this is nothing to fool around with in any case, but when it's been mistreated like this, it's like juggling a rattlesnake.

PLus at this point, with the soft start going up in flames, the primary wiring could be melted, as well as the secondary wiring to the outputs.

Pull and test:
1. output transistors, 8 of them plus associated components and possibly wiring
2. driver transistors, 4 of them with associated components as well
3. bias transistor circuits, probably.. hopefully the four bias diodes (stv-3h) are ok, those are VERY hard to find.
4. power supply regulator transistors if you WEREN'T lucky
5. whatever primary circuit wiring was fried.

The guy who put this up as parts knew what he was doing.

It can be done. It'll be expensive, AND a PITA.

How much did you spend for it?

At what point will it be too expensive to fix?

Do you have a DMM with a diode test? Do you know how to test transistors with a DMM diode test?

It will be a LONG time before the power is turned back on.

Take a long good look at the wide pc board in the back, mounted to the heatsinks, you will be getting INTIMATELY familiar with it and everything mounted on the heatsinks.

Did you even get the service manual?
Click to expand...


Got the parts one for $50.00 got it as a spare for parts if ever needed as I already have a pristine like new SX-1050 got from an AKer that sounds and works great. May even take the tranformer out the junk one for a active Subwoofer project. I know this thing is worth $$$$ in parts alone. The wood is in 90% and the nobs glass etc are all real nice. I thought since it looks so nice it may be worth it to get it back into service again. Perhaps this is something I will really take my time on. I know parts are very expensive for these so I figure for $50 it was worth in just the parts I can see. I already have the service manual for it that is how I was able to id what was smoking. Have Fluke DMM, old tube scope and a cheap china meter with Transitor checker that I do not trust.
ALL in all just getting some idea what could be wrong or tips on trouble shooting it is what I was looking for.
Thanks for your input. You gave me a good starting points, great ideas and some things to look at.
-Jim
 
When you are done selling the good stuff and are ready to toss the rest, let me have the rest instead of tossing it.
 
Honestly, this is repairable without a great deal of effort...it obviously has toasted outputs, and will probably need a new soft-start resistor, but there's nothing here that would convince me that this is a parts unit.
 
Echo, Is the resitor you refer to the part that is smoking or are you refering to a different part ???? ........The part that is smoking is part of the Surge current suppressor Assembly AWX-098 ?
What all is included in the soft start ? which assemblies are part of the soft start ?
Do you think anything happend to Power Supply Assembly A or B ?
Sorry for all the dumb questions I am new to this.
thanks Jim
I think it is the 3.3ohm 20W resitor on AWX-098 that is smoking??
 
Echo sure knows how to spoil a good parts party! All in good fun, I'm not really looking for parts for any SX-1050's. I'd just had a couple of light drinks and thought I'd make a funny.:yes: Brad
 
bowtieman427 said:
I think it is the 3.3ohm 20W resitor on AWX-098 that is smoking??
Click to expand...
That's right. All input current is routed through this resistor until the power supply charges, then there's a relay mounted next to the board that takes the resistor out of the circuit (takes about 1/2 a second after power-up for all this to happen).

The resistor may not be bad, yet. But if you want to troubleshoot this, you need a dim-bulb tester (light-bulb fixture in series with the power cord to limit current).

I got your PM, but I'll tell you here that swapping out the entire amp assembly is very likely harder than fixing what you have. Pioneer used solid-core wirewrap for all the connections to that amp board, and to shoehorn a new one in place means a lot of solder-blobbing to attach the new wires. Always looks like hell, and since I'm on a personal mission to eradicate solder-blobbing, I say fix the amp that is in it, or have it fixed.

All the output transistors need to be pulled and tested before you even think of trying to power it up again, and when you do, it needs to be on a current-limited supply, such as the dim-bulb tester.
 
This may be a real noob question but what is a dim-bulb tester ? Also I need to limit the current what about. Any concerns on voltage during bring up ?
Perhaps the use of a variac will be needed. I will work on geting the transistors out and get them checked.
Thanks agian for all you help
Jim
 
bowtieman427 said:
This may be a real noob question but what is a dim-bulb tester ? Also I need to limit the current what about. Any concerns on voltage during bring up ?
Perhaps the use of a variac will be needed. I will work on geting the transistors out and get them checked.
Thanks agian for all you help
Jim
Click to expand...

An incandescent lightbulb is inserted in series with the power line, like a 120v line fuse. If there is too much current drawn the bulb will continue to glow brightly, absorbing much of the power that would otherwise cause damage elsewhere in the unit.

Normally that energy would cause the fuse to pop, usually way too late....

In a functioning unit, the bulb will glow brightly for a few seconds as the capacitors store up energy, then the bulb will grow dim as the power draw on the line drops. If it doesn't dim, there is a problem.

Thus the description: "dim bulb tester".
 
Variacs don't limit current, which is why a dim-bulb tester with a 100W bulb is the way to go.
 
OK I did somehing risky tonight I took the 8 output transistors out of the circuit and powered up all came on like normal relays worked and all the lights came on. NO SMOKE :yes: I then took the transistor assembly out completly out. How do I test them ? All I have is a DMM.
I was wondering if I could just find the bad ones looking for a short but I also figure if one shorted it may have tackin something with it.
thanks
Jim
 
bowtieman427 said:
OK I did somehing risky tonight I took the 8 output transistors out of the circuit and powered up all came on like normal relays worked and all the lights came on. NO SMOKE
thanks
Jim
Click to expand...

It is said the Almighty protects fools and drunks..... I said it will be a long time before power is turned back on. DID you AT LEAST rig a dim bulb tester for protection???

The last few fellas that jumped ahead on me in troubleshooting threads did a LOT more damage to their units.

Those were well thought out instructions I posted way back.

bowtieman427 said:
OK I did somehing risky tonight I took the 8 output transistors out of the circuit and powered up all came on like normal relays worked and all the lights came on. NO SMOKE :yes: I then took the transistor assembly out completly out.
thanks
Jim
Click to expand...

Are the transistor sockets still connected to the board, and since the transistors are not in the sockets, they could come loose from the heatsink assembly? I hope you marked where each of the old ones came from......

I REALLY hope you didn't unwrap any of those connections. (Nobody said NOT to, but...)

bowtieman427 said:
How do I test them ? All I have is a DMM.
I was wondering if I could just find the bad ones looking for a short but I also figure if one shorted it may have tackin something with it.
thanks
Jim
Click to expand...


markthefixer said:
Pull and test:
1. output transistors, 8 of them plus associated components and possibly wiring
2. driver transistors, 4 of them with associated components as well


Do you have a DMM with a diode test? Do you know how to test transistors with a DMM diode test?
Click to expand...

????????

When part of a response is underlined, it is a LINK to something else. If somebody took the time to go and GET a link to something. it should be considered vital information.

There are at least two output transistors blown, and because transistor matching is important in a high power amp for load sharing, you should replace all 8. AND when replacing them they NEED the old white goo cleaned off, and new applied. Also there are insulators between the transistors and the heatsink... be very careful with them, they will crack and break. If the three transistor leads are NOT insulated electrically from the heatsink, the short circuit will destroy things fast.

from mouser.com you will need:
four: 863-MJ21194G to-3 NPN 250v 16A 250W 4mhz 8-75hfe $4.10 each
four: 863-MJ21193G to-3 PNP 250v 16A 250W 4mhz 8-75hfe $4.10 each
ten: 534-4662 mica insulators $0.16 each (two spares)
one: 532-249 1 oz thermal compound $4.71

more will be added to this list...


bowtieman427 said:
How do I test them <snip> but I also figure if one shorted it may have tackin something with it.
thanks
Jim
Click to expand...

Thus the step 2:
markthefixer said:
Pull and test:
1. output transistors, 8 of them plus associated components and possibly wiring
2. driver transistors, 4 of them with associated components as well
Click to expand...

1: associated components R61-R68 all 0.5 ohm 5 watt resistors, R57-R60 10 ohms 2 watt resistors.
2.a.: Q17, Q18, Q19, Q20 which are the 1/2 inch square transistors mounted on the little heatsinks on the amplifier board.
2.b.: Q13, Q14, Q15 & Q16 which are little water droplet sized transistors on the amplifier board
 
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