DC at speaker terminal help

[frankfurts]

Hey guys I'm new here and new to working on amps

I have a line 6 spider III 15watt amp which had a problem where it was extremely quiet even when cranked. I figured I would pull it apart check for anything obvious then put it back together.

Upon putting it back together I managed to release the smoke stored in the electronics. I found a fries diode and replaced it, I also checked the other diodes and all good.

Now I turn it on I get a hum from the speaker, checked and found I had 10V DC there.

I also checked the power amp which had a 13V DC supply and 11V DC output. Input was about 0.8V and volume was all the way down.

I studies electronics a long time ago so I am comfortable with replacing components but would appreciate if you guys can help to guide me through the trouble shooting process

[Enzo]

I forget, is the power amp IC a TDA7293 or an LM3886?  Either way, look up the data sheet for the part to see which pins are what.  Then verify that both positive and negative power supplies are up to the same voltage and frree of ripple.   Perhaps you are missing the negative supply?

If you have good power supplies, then most times any power amp failure is simply a bad power amp IC.

[Roly]

Hi frankfurts, Welcome!


DO NOT turn the amp on again.  Only more damage will result.

DISCONNECT the loudspeaker and do not reconnect until the diagnostics tests show the repair is complete.

You will need to make up some form of Limiting Lamp so that you can liven it up for testing without damage.

Even with a serious blow up this class of amp is normally quite repairable.

[frankfurts]

Thanks for the replies. I'll make myself a limiting lamp and do some more tests.

The poweramp is a TDA2030

I don't have a cro but I assume I can check for ripple of its bad enough by switching my meter to AC?

[g1]

Yes, you should be able to measure ripple on the AC range, unless it is a real cheap meter that can't measure AC on DC.  You can check by measuring a AA or 9V battery with the AC range, it should read 0V AC.  If so, you should be able to measure ripple with it.

Even with a serious blow up this class of amp is normally quite repairable.

If you mean the power amp, I agree  .  But there is still the original fault, which I don't think was power amp, and in this regard Line6 stuff can be non-repairable.
So there remains the possibility of going to all the trouble of repairing the power amp only to find you need a new "mainboard"  :grr.

[frankfurts]

Well I just bought stuff to build my bulb limiter then I'll try some fault finding.

I'm not sure how I smoked the diode initially as once pulled apart everything just plugs/screws into place it physically won't fit any other way.

I'm thinking maybe a bit of ESD may have been the cause.

Now when I work on it I have the mains plugged in but switched off at the wall so that whilst I'm touching the frame I am earthed.

[Enzo]

A TDA2030 is simpler still than the others.

If you remove the IC, you can fire up the amp without it and check the rest of the voltages.  There should not be DC on either input pin.

[frankfurts]

OK tested the power amp pins 5 (+ve) and 3 (-ve) and I have about 21V on the +ve and 0.9V on the -ve.

Showing only about 10mv on AC so that parts good. Just trying to find the test points after the rectifier. I can see a row of 6 diodes and also a row of 2. I have no schematic though.

I thought a bridge would only be made of 4.

Appreciate the help by the way hopefully I can get this baby going again.

[frankfurts]

I also have +20V DC on the O/P pin (pin 4) the inputs all have less than 1 V

[Enzo]

So find out where the negative supply went, nothing works without good power supply.  If only +20 is applied to the IC, then all that can appear on its output is +20.

[frankfurts]

So find out where the negative supply went, nothing works without good power supply.  If only +20 is applied to the IC, then all that can appear on its output is +20.

Thanks for the help, doesn't seem as terminal as I first thought when I saw smoke come out

Does anyone have a schematic for this amp? I can't find one. I'm confused with all the diodes as I thought you only need 4 for a full wave rectifier not 8. Or do they have 2 DC voltages? 1 from the center tap of the transformer?

[Roly]

I'm thinking maybe a bit of ESD may have been the cause.

Don't spin your wheels - you don't even know what is actually wrong yet (and some random short is a more likely cause).

OK tested the power amp pins 5 (+ve) and 3 (-ve) and I have about 21V on the +ve and 0.9V on the -ve.

You have the +ve supply but not the -ve supply.  (Ripple is the least of your problems ATM)


I'll try and attach the circuit.  On page 3 are the power supplies;

- main supply using four diodes in a bridge with a centre-tapped tranny to end up with a bi-polar supply for the power amp, +HI and -HI;

- these are regulated down to provide +VA and -VA which are around 9V;

- a mono-polar bridge rectified supply +VL of around 12-15V; and

- a 3.3V monopolar supply regulated down from +VL for the DSP/Fx board.

HTH

{it won't take the upload, helpfully telling me the file is already here, but unhelpfully not telling me where it is.}

[frankfurts]

What a pain. If I could look at the diagram it would be much easier to test the diodes as they are all numbered on the board. I'll give it a go though with my trusty pen and paper

[Roly]

As DeCastro said when writing about dBase-II, "Water is wet, rocks are hard, and software has bugs."  You can sit and complain about the state of things, or you can try to find a work-around.

This forum software, good 'tho it is, isn't cutting it for our needs, so we try something different...

A) try this;

http://www.schematicsunlimited.com/l/line-6/line6-spider-15w-ii3012-1508-amplifier-schematic


B) failing that, try Googling <line6-spider-15w-ii3012-1508-amplifier-schematic.pdf>

[frankfurts]

Cheers mate I have the spider 3 but I think the basics supply should be near identical. I'll have a look.