Home stereo amplifier issue - dummy needs advice

Thread Starter

Bluewater34

Joined Dec 27, 2020
9
Hi,

I’m sure you veterans love this next line: I’m new here, found your site when looking up an issue. I’m not proficient with electronics but can solder well and take instructions.

I googled the following, which led me here: “my AudioSource Amp300 makes a spark when I power up”. Someone had the exact same issue four years ago and posted it here. https://forum.allaboutcircuits.com/threads/home-audio-amplifier-repair.128825/page-3

There was good discussion and I did what the author did to fix the problem. Only I powered up one more time and this happened: 2A2EE422-EA81-4AB9-BA42-74800EEC3584.jpeg

There was a bigger spark, some smoke, and ceramic disc cap carnage. I don’t know if the spark came from the disc cap or if it hit the disc cap and broke it up. Needless to say, the cap (and it’s neighbor) are toast. I hope the relay (Goodsky) is ok. I guess I should say here where all this is inside the unit. It’s on the transformer side, right next to the transformer and the bank of big tall capacitors. Obviously all this is right in line with the on/off switch. The spark wouldn’t happen if I turned if off and right back on. Only happened when it was cold and I fired it up. Last week I did some PM on the unit with a can of air and some De-Ox. This sparking business happened after my PM/cleaning.

My plan is to replace the two little disc caps and try it again - unless y’all think it’s something else and I shouldn’t do this. It’s my assumption that the ceramic capacitors were bad replacing them will solve it. I don’t believe this myself - but it’s my hope. Just so you know, I was thinking the spark was coming out from under that bridge with the little heat sink on it before this major one that wrecked the cap(s). And yes, I have no idea what I’m doing. I’m going to get some new ones tomorrow at the electronics store that say 104 on them, like these burned up ones and replace them.

Some other observations: the big canister capacitors and even the small ones show no signs of bulging or leaking. I’ve replaced those in speakers often. The underside of the PCB shows zero signs of trouble - no burns, no discoloration, no nothing. I can take more pics if needed. Also, I was had the GoPro set up recording when I turned it on. I caught the pop in 4k - only I was filming from the wrong side. Glad to share still shots from that if you want - doubt it will help much.

Any advice??
 

Thread Starter

Bluewater34

Joined Dec 27, 2020
9
Hi,

I’m sure you veterans love this next line: I’m new here, found your site when looking up an issue. I’m not proficient with electronics but can solder well and take instructions.

I googled the following, which led me here: “my AudioSource Amp300 makes a spark when I power up”. Someone had the exact same issue four years ago and posted it here. https://forum.allaboutcircuits.com/threads/home-audio-amplifier-repair.128825/page-3

There was good discussion and I did what the author did to fix the problem. Only I powered up one more time and this happened: View attachment 226049

There was a bigger spark, some smoke, and ceramic disc cap carnage. I don’t know if the spark came from the disc cap or if it hit the disc cap and broke it up. Needless to say, the cap (and it’s neighbor) are toast. I hope the relay (Goodsky) is ok. I guess I should say here where all this is inside the unit. It’s on the transformer side, right next to the transformer and the bank of big tall capacitors. Obviously all this is right in line with the on/off switch. The spark wouldn’t happen if I turned if off and right back on. Only happened when it was cold and I fired it up. Last week I did some PM on the unit with a can of air and some De-Ox. This sparking business happened after my PM/cleaning.

My plan is to replace the two little disc caps and try it again - unless y’all think it’s something else and I shouldn’t do this. It’s my assumption that the ceramic capacitors were bad replacing them will solve it. I don’t believe this myself - but it’s my hope. Just so you know, I was thinking the spark was coming out from under that bridge with the little heat sink on it before this major one that wrecked the cap(s). And yes, I have no idea what I’m doing. I’m going to get some new ones tomorrow at the electronics store that say 104 on them, like these burned up ones and replace them.

Some other observations: the big canister capacitors and even the small ones show no signs of bulging or leaking. I’ve replaced those in speakers often. The underside of the PCB shows zero signs of trouble - no burns, no discoloration, no nothing. I can take more pics if needed. Also, I was had the GoPro set up recording when I turned it on. I caught the pop in 4k - only I was filming from the wrong side. Glad to share still shots from that if you want - doubt it will help much.

Any advice??
E86294B4-10C2-42BC-A558-DA0DF6756CA0.pngI decided to post a still of the “explosion”. This is the brightest part.
 

Hymie

Joined Mar 30, 2018
976
As a general rule of thumb – a voltage of 1kV can jump a clearance of 1mm, in reality it takes a greater voltage than this.

The amplifier is using a linear transformer with the secondary reservoir capacitors rated at 80Vdc. Therefore under normal operation the peak voltage difference (primary to secondary) will be a maximum of 400V (based on a 240V mains supply).

But the spark in your video and the posted link would need a voltage difference of at least 3kV (IMO). The only way this could be developed is if the transformer windings are being switched on/off rapidly (causing a collapse in the transformer magnetic field, generating the peak voltage pulse). Therefore I would suspect the relay (white component) is switching in and out for some reason (switching the input or output of the transformer).

Normally high power linear supplies use a relay to switch out a resistor used to limit the peak reservoir capacitor charging current at initial switch on. This resistor may have failed open circuit causing the issue.
 

MisterBill2

Joined Jan 23, 2018
8,727
A whole lot depends on where that device that looks like a capacitor is located in the circuit. I have come across varistors that have failed short circuited and popped a fuse, and after replacing the fuse and removing the short circuited varistor the receiver played perfectly for many years. Many varistors look a whole lot like disc capacitors, and so lead to a lot of confusion.
If a bridge rectifier has failed that would be a totally different situation, I am not sure why that even got into the discussion.
One simple thing would be to simply clip out the failed part and see if the amplifier still works.

Now that I examined the photo again I see a mark indicating that the device is a capacitor. If we knew what the connections to the nearby terminals are and if we can see the connections to the terminals and capacitors on the bottom side of the circuit board then an additional conclusion could be reached.
 

Thread Starter

Bluewater34

Joined Dec 27, 2020
9
First of all, thanks to everyone for joining in. Please remember my limited experience with electronics - basically the sum total of my experience is simply changing out capacitors on old speakers and even old receivers, just to update them. There’s a store nearby that can fix my problem, I’m trying to get good at this on my own. Your dumbed down advice is welcome.
 

MisterBill2

Joined Jan 23, 2018
8,727
OK, So now here is an educational request, which is to look at the foil side of the circuit board and see if the connections from those failed capacitors connect to the nearby connectors. Then let us know what the circuits are that go to those connectors. If they are, then probably you can just remove those small capacitors remains and all will be OK.
 

bassbindevil

Joined Jan 23, 2014
158
That's a strange problem. Could arcing at the relay contacts combine with transformer inductance to create a high-voltage spike?
If the schematic in the earlier discussion applies to this amp, there is no soft-start resistor; the relay just switches the transformer secondary.
 

Thread Starter

Bluewater34

Joined Dec 27, 2020
9
OK, So now here is an educational request, which is to look at the foil side of the circuit board and see if the connections from those failed capacitors connect to the nearby connectors. Then let us know what the circuits are that go to those connectors. If they are, then probably you can just remove those small capacitors remains and all will be OK.
Thanks MisterBill2, I did flip the board obviously and the soldering all looked great and there was zero signs of trouble from the arcing on that side. So I went to the local store and bought new capacitors to replace those that were burnt and said “104” on them. The guy there guessed that the burned up ones were 250v and only had some bigger ones - he said they’d be fine as long as I could physically fit them in. These are 630v. I had the space to fit them in, though it looks ugly as both are leaning away from each other. I did a good soldering job. Hooked it all back up and put the GoPro on it in case there was a new spark. There wasn’t. It worked as normal. I’m so glad it’s repaired, but at the same time a little sad that it wasn’t more than that - I didn’t learn much. Thanks so much for everyone’s help.

PS - there seems to be an empty resister space just to the left of the black wire. I didn’t move it - is that weird?

5E2822C7-405C-4FCA-93B9-26258F8BC667.jpeg
 

jpanhalt

Joined Jan 18, 2008
11,088
You probably know that a capacitor marked "104" is a 0.1 uF capacitor. If not, that might help when or if there is another failure.

I liked Hymie's comment, because it was not simply a guess at the problem but a logical "pathophysiological diagnosis," to borrow a term from biology. Of course, it may well be completely wrong, but I would not forget its message should the problem recur.
 

Thread Starter

Bluewater34

Joined Dec 27, 2020
9
You probably know that a capacitor marked "104" is a 0.1 uF capacitor. If not, that might help when or if there is another failure.

I liked Hymie's comment, because it was not simply a guess at the problem but a logical "pathophysiological diagnosis," to borrow a term from biology. Of course, it may well be completely wrong, but I would not forget its message should the problem recur.
Definitely, I took the path of least resistance in this case. I saw two burned up ceramic disc capacitors and figured they needed replacing - but in the back of my head I thought they had been destroyed by a different problem, not that they had gone bad. So I really didn’t listen to myself and got lucky. I truly thought the arc was coming from under that bridge rectifier with the wire posts. Maybe that’s where the arc went, not came from??? In any case, problem solved but in a cheap and non-learning way. I have a trashed out amp that I may pull apart to see if I can get it going again - that would truly be a good learning experience. This stuff is fascinating to me, but there’s SO MUCH to learn it seems really intimidating.
 

Hymie

Joined Mar 30, 2018
976
Looking again at the toroidal transformer it has two blue, two brown and a grey wire located close together. These are almost certainly the primary wires, and therefore the amp appears to be configured to switch automatically between 120V and 240V operation*. And therefore the arcing might be due to the voltage selection relay switching in and out as a result of a fault (switching between 120/240V operation).

* the amp’s marked rated input voltage should read 120/240V with the amp having no manual voltage selection switch.
 

jpanhalt

Joined Jan 18, 2008
11,088
Ceramic and metallized film (e.g., polyester, Mylar ) capacitors have very low failure rates after the first 100 hours or so. That is quite different than the large aluminum electrolytes that have increased failure rates with age.

Like I said/implied, those capacitors may only be acting as fuses. If it fails again, look for a root cause.
 

MisterBill2

Joined Jan 23, 2018
8,727
This is the first I have heard about an automatic voltage selection function. On all of the amplifiers that I have ever worked with that had a relay, it was a speaker protection relay to avoid that massive thump when the amp is switched on.

An automatic voltage selection relay is a new one on me. Does this amplifier really have that feature? Or is that just a guess.

And when I suggested looking at the foil side of the board it was NOT to check for damage, it was to look at connections to see what those capacitors were connected to. That is quite a big difference.
 

Hymie

Joined Mar 30, 2018
976
It is an educated guess that the amplifier has automatic mains input voltage selection – otherwise why take the two independent primaries (brown/blue wires) to the PCB.

Having stated that something is generating voltages of at least 3kV to cause the arcing, the only possible source is the collapsing field of the transformer windings.

If some fault were to occur in the input voltage selection relay circuitry, causing the relay to switch between the two input voltage settings – this could very well be the source of the high voltage spikes.
 

Thread Starter

Bluewater34

Joined Dec 27, 2020
9
This is the first I have heard about an automatic voltage selection function. On all of the amplifiers that I have ever worked with that had a relay, it was a speaker protection relay to avoid that massive thump when the amp is switched on.

An automatic voltage selection relay is a new one on me. Does this amplifier really have that feature? Or is that just a guess.

And when I suggested looking at the foil side of the board it was NOT to check for damage, it was to look at connections to see what those capacitors were connected to. That is quite a big difference.
Ahh, I inferred that you wanted to see if there was any discoloration on the back side of the PCB, not for mapping. Sorry. Now that it‘s all fastened back up and back in the rack, I think I wont be taking that panel back out again, unless there’s a new problem. However, the reason i‘m on this site is from a google search that led me here as it showed me someone that had the exact same issue and posted on allaboutcircuits.com. I tried to link it above, but somehow it goes to the relay spec sheet. If you search this site for “home audio amplifier repair” it will take you to the thread I found about this issue with this amp. He had taken pics of the underside of the PCB and it looks identical to mine. I’ve attached it. 56C37BA1-39B9-4F0C-A2E9-C5B05C45B69A.png

Sorry, not sure how to draw lines to where this all happens on the pic. Basically the two caps that I changed out in this pic are on the left lower side just above the three pins that are by themselves.

816182C0-4469-43B8-95EE-FCFD0D73F3A3.jpeg
 

MisterBill2

Joined Jan 23, 2018
8,727
OK, the caps were in the power input section, which explains why there was enough power available to destroy them. They broke down for whatever reason and then the line current did the exploding. The new ones with that 630 volt rating will probably outlast the rest of the amp now. Those rated eor only 250 volts were rather too close to the peak voltage for my comfort.
 

Hymie

Joined Mar 30, 2018
976
That photo of the input rating confirms that the amp has automatic mains voltage selection – my theory of the voltage selection relay switching, as being the fault is looking good, but precisely what is causing it is another issue.
 

Thread Starter

Bluewater34

Joined Dec 27, 2020
9
OK, the caps were in the power input section, which explains why there was enough power available to destroy them. They broke down for whatever reason and then the line current did the exploding. The new ones with that 630 volt rating will probably outlast the rest of the amp now. Those rated eor only 250 volts were rather too close to the peak voltage for my comfort.
Ok, this was also my concern. I didn’t think the caps were undersized, just not beefy enough for years of service. Thanks for looking over my shoulder on this one. So far, working fine now.
 
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