Hey guys, I'm new to the forum. I just bought an Infinity SSW-212 subwoofer that had a dead amp (doesn't power on, the fuse is fine). I bought it because the woofers were in god physical condition, it was cheap, and I supposed I might be able to fix it. After visually inspecting the entire circuit board, I only saw one visible problem: the inrush current limiter seems to be blown. I'm rather new to DIY electronics repair, but I found this part on digikey and want to verify that it would work as a replacement: Digi-Key - 570-1032-ND (Manufacturer - SL22 10005)
The amplifier itself has a line-in fuse that is 120V, 5A, 3AG slow blow. I have a feeling that ICL on digikey will work, since it's the same part number as what is printed on the blown ICL and it is rated for 5A.
Please let me know if that's correct! I'm really hoping replacing this piece will fix it because it's cheap and a really easy solder job.
Below are pictures of the blown ICL from my amp, including the part number stamped on it.
View of the ICL... you can see that it doesn't look quite right 🙂
A closer view of the ICL, showing the damage.
The other side of the ICL showing the part # (it reads "USS 10005").
Thanks in advance guys,
- Brett
The amplifier itself has a line-in fuse that is 120V, 5A, 3AG slow blow. I have a feeling that ICL on digikey will work, since it's the same part number as what is printed on the blown ICL and it is rated for 5A.
Please let me know if that's correct! I'm really hoping replacing this piece will fix it because it's cheap and a really easy solder job.
Below are pictures of the blown ICL from my amp, including the part number stamped on it.
View of the ICL... you can see that it doesn't look quite right 🙂
A closer view of the ICL, showing the damage.
The other side of the ICL showing the part # (it reads "USS 10005").
Thanks in advance guys,
- Brett
yeah, that thermistor looks broken! and the one from Digi Key looks just fine to replace it. But it is not to often to see a thermistor broken like that. it must be a big "inrush" to break one like that.
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You might want to go up a step on the current rating for the replacement part. Also see if you can figure out why it blew - does the bypass relay work? Does the timer circuit that triggers the relay work? Is there a short circuit downstream from the transformer? Etc.
It could be that the part was under spec'd and hit end of life, or that it had some manufacturing defect that made it die an early death. But it would be prudent to check the rest of the supply and amp to see if there was some other cause and the thermistor was the weakest link and therefore first to go. Don't make any assumptions based on the fuse being good, when the amp died that was probably the first thing that the person you bought it from tried.
It could be that the part was under spec'd and hit end of life, or that it had some manufacturing defect that made it die an early death. But it would be prudent to check the rest of the supply and amp to see if there was some other cause and the thermistor was the weakest link and therefore first to go. Don't make any assumptions based on the fuse being good, when the amp died that was probably the first thing that the person you bought it from tried.
Thanks for the replies! Indeed, the original owner saw the fuse was blown and replaced it (which obviously did not fix the problem). I would assume the fuse and the thermistor went at the same time (possibly a power surge).
I agree it would be prudent to perform more testing. I don't know much about electronics, but I don't think there is a timer circuit (this sub has no auto-on/off function). How would I do a more thorough test for shorts? Again, visibly there is no indication of a short anywhere on the board. The only visible damage is with the thermistor.
If I were to step up the current rating, how high should I go, and what would be the consequence of going too high? If the amplifier is rated for 5A max, wouldn't I want to limit the inrush current to 5A?
Thanks again,
- Brett
I agree it would be prudent to perform more testing. I don't know much about electronics, but I don't think there is a timer circuit (this sub has no auto-on/off function). How would I do a more thorough test for shorts? Again, visibly there is no indication of a short anywhere on the board. The only visible damage is with the thermistor.
If I were to step up the current rating, how high should I go, and what would be the consequence of going too high? If the amplifier is rated for 5A max, wouldn't I want to limit the inrush current to 5A?
Thanks again,
- Brett
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you can go higher with the thermistor but, never go higher with the specified fuse.if anything goes wrong the fuse will burn.
Cool. I ended up ordering the 5A thermistor just to replace what was there. If it ends up blowing later I'll get one rated for a little more amperage. As for the fuse, I could only find 5A 3AG slow-blow rated for 250V (checked mouser and digikey), despite the owner manual specifying 125V. From what I understand, it's ok to have a fuse be rated for a higher voltage... I could be wrong though :| We'll see what happens!
Typically the thermistor is in parallel with a relay. When the switch is first turned on, AC flows through the thermistor to the transformer and then to the power supply, limiting the inrush current. After a few seconds the relay is turned on shorting across the thermistor, so the AC current flows through the relay to the transformer for all but the first few seconds after power-on. A simplified schematic and spice model is here: AC to DC Power Supply - diyAudio (got to put in a plug for the LTspice wiki.)
So look for the relay, then check that the relay is getting turned on a few seconds after the unit is switched on. You wouldn't want your sub amp to be sucking current through the thermistor full time - that would limit performance and mean an early death for the thermistor.
So look for the relay, then check that the relay is getting turned on a few seconds after the unit is switched on. You wouldn't want your sub amp to be sucking current through the thermistor full time - that would limit performance and mean an early death for the thermistor.
Just to give an update. There is no bypass relay. Current goes straight through the thermistor always. Basically current flows like this: line AC -> fuse -> thermistor -> switch.
Anyway, I got the new thermistor and put it in. I plugged in the amp, flipped the switch, and... the fuse blew. Thermistor is fine. I'm hoping no components were damaged.
I found the schematic for my amp online for $1 (I should have bought it sooner), and it actually shows a thermistor with a resistance of 20 ohms. Would using the 10-ohm thermistor cause the fuse to blow (by letting in too much current)?
On digikey, the only 20-ohm 5A ICL has a tolerance of +-25%. I saw a 30-ohm 5A ICL with +-15%. Would using a 30-ohm thermistor cause problems or should I just get the 20-ohm?
Anyway, I got the new thermistor and put it in. I plugged in the amp, flipped the switch, and... the fuse blew. Thermistor is fine. I'm hoping no components were damaged.
I found the schematic for my amp online for $1 (I should have bought it sooner), and it actually shows a thermistor with a resistance of 20 ohms. Would using the 10-ohm thermistor cause the fuse to blow (by letting in too much current)?
On digikey, the only 20-ohm 5A ICL has a tolerance of +-25%. I saw a 30-ohm 5A ICL with +-15%. Would using a 30-ohm thermistor cause problems or should I just get the 20-ohm?
For some reason I can't edit my post. The 30-ohm thermistor I found has a +-20% tolerance, not 15.
Also, I am aware there might be a short somewhere, but I haven't done a thorough check yet. I might be able to get an electrical engineer friend of mine to come help me find the short.
It sounds like the thermistor isn't the problem, most likely there is a short circuit somewhere, perhaps a shorted output transistor in the amp.
Get a multimeter, and start by disconnecting the transformer from the rest of the power supply. Replace the fuse, and then make sure you have the proper AC voltage at the output of the transformer. Check the rectifier diodes - typically these fail open, but check anyway. Do a visual inspection of the power supply capacitors, look for any bulging or leaking electrolyte. If all of that looks good, then disconnect the power suppy output from the amplifier, hook the transformer back up, and then check the DC output of the power supply.
If you can switch on the power supply without the amplifier circuit connected and you get proper DC levels, then chances are one or more of the output transistors is blown. Post a pdf of the schematic here and we can have a look.
Be careful messing around inside the amp - AC line voltage at best can give you a very nasty shock, at worst it can be lethal. The bulk capacitors in the power supply can hold a charge for a very long time, and depending on the voltage can be very dangerous. If there are no bleeder resistors across the bulk capacitors, then it is a good idea to short across the caps with a screwdriver to make sure they are discharged before working inside the chassis.
Get a multimeter, and start by disconnecting the transformer from the rest of the power supply. Replace the fuse, and then make sure you have the proper AC voltage at the output of the transformer. Check the rectifier diodes - typically these fail open, but check anyway. Do a visual inspection of the power supply capacitors, look for any bulging or leaking electrolyte. If all of that looks good, then disconnect the power suppy output from the amplifier, hook the transformer back up, and then check the DC output of the power supply.
If you can switch on the power supply without the amplifier circuit connected and you get proper DC levels, then chances are one or more of the output transistors is blown. Post a pdf of the schematic here and we can have a look.
Be careful messing around inside the amp - AC line voltage at best can give you a very nasty shock, at worst it can be lethal. The bulk capacitors in the power supply can hold a charge for a very long time, and depending on the voltage can be very dangerous. If there are no bleeder resistors across the bulk capacitors, then it is a good idea to short across the caps with a screwdriver to make sure they are discharged before working inside the chassis.
I'll try everything you suggest later tonight when I'm home. I've already visually inspected the capacitors and they show no visible sign of damage. I'll discharge them tonight and check them with my multimeter.
Here's a link to the PDF (it's two pages but they are overlapping... apparently it couldn't all fit on one page when they scanned it): http://dl.dropbox.com/u/10756584/SSW212_SUBWOOFER.pdf
I appreciate you all being so helpful. This task definitely ended up being above my skill level, but I'm enjoying the learning experience.
Here's a link to the PDF (it's two pages but they are overlapping... apparently it couldn't all fit on one page when they scanned it): http://dl.dropbox.com/u/10756584/SSW212_SUBWOOFER.pdf
I appreciate you all being so helpful. This task definitely ended up being above my skill level, but I'm enjoying the learning experience.
Shorting across caps with a screwdriver can be very dangerous.
I would make up a resistor with two long leads and use that to discharge any caps.
I would make up a resistor with two long leads and use that to discharge any caps.
Another update... I tested the capacitors. They were already drained (checked with my multimeter first). The capacitor C28 (named such on the schematic) had no initial resistance and did not charge when testing my multimeter. I tested C29 and it was fine (had high initial resistence and charged). I took C28 off the PCB and tested the leads and it was actually fine (charged up and held the charge). There's a short somewhere else. When I attached C28 to the PCB again, it no longer held a charge and read 0 on my ohm meter. I tested continuity between the now-empty + and - solder points where C28 sat, and there is continuity. Now I need to hunt for the short. I guess I've narrowed it down to a particular section of the circuit, at least...
Also, mod, is it possible to rename this thread to something more appropriate? I'm embarrassed by the title I gave it now that it became a big adventure 🙂
Also, mod, is it possible to rename this thread to something more appropriate? I'm embarrassed by the title I gave it now that it became a big adventure 🙂
OK guys... I feel like such an idiot. What's missing from the picture? Just the AMPLIFIER. I can't believe I didn't notice that before. I seriously feel dumb 🙁 The part is an STK-4050V and I can get it online for like $15. But where the heck did it go? Why did the previous owner take it? Oh well... I still need to find the short, though. I'm about to check the rectifier diodes, but I just had to share this!
Take a look at what's missing:
Take a look at what's missing:
An externally hosted image should be here but it was not working when we last tested it.
Just another update. As mightydub suggested, I ended up finding that one of the rectifiers (D3 on the schematic) was shorted. There don't seem to be any more shorts in the circuit. I ordered a replacement rectifier and a replacement STK-4050V. Once the rectifier comes I'm going to put it in, test for shorts, then try powering on the power supply. If that doesn't cause anything bad to happen, I'll install the STK-4050V. I'll post again once I've done these things.
Check the subwoofer itself. Depress the cone - does it grate? If so, it's toast and if you put in a new chip, the chip will just die. The previous owner obviously removed the chip to test it or something.
Haha, yeah if the woofers were bad it would make the whole project basically pointless. I can verify that the woofers are good. I depressed the cones before I even bought it to make sure they weren't obviously damaged. I checked them with an ohm-meter later and they were each about 8 ohms. Finally, I hooked them up to a receiver I have just to see if I get sound out of them and they are both good.
Good looking out, though 🙂 I didn't check them with a multimeter until a coworker told me I should (that was another "duh" moment).
Power Input Current Limiter.
Put a 40W or 60W lamp in series with the 110V supply (or across the fuse holder and fuse removed) and no signal input before initial switch on to confirm that DC operating conditions are correct.
If the lamp glows brightly you still have a fault.
If all is ok (lamp glows dimly) refit fuse and connect signal and try it out.
Eric.
Put a 40W or 60W lamp in series with the 110V supply (or across the fuse holder and fuse removed) and no signal input before initial switch on to confirm that DC operating conditions are correct.
If the lamp glows brightly you still have a fault.
If all is ok (lamp glows dimly) refit fuse and connect signal and try it out.
Eric.
Looks like you're on the right track to getting the problems sorted out and you'll soon have a working subwoofer for cheap. Careful or you'll end up getting sucked into this hobby like the rest of us - if you start thinking "how can I get more bass?" or "how would it sound if I..." get yourself to rehab quick.
Not to keep bumping this thread, but I need to give another update. I finally received the replacement rectifier diode and installed it on the PCB. NOW I can turn on the power supply and it stays on... no shorts or blown fuses! Woohoo! So now I am waiting for the amplifier which was mysteriously missing. I will post one more update when that is installed and tested. Hopefully it will be my last post about this.
Pretty much... I'm now thinking about other electrical devices I can try fixing. I'm having a blast with this project!
Pretty much... I'm now thinking about other electrical devices I can try fixing. I'm having a blast with this project!
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