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Old 12-29-2018, 01:43 PM   #1
benV
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Default Kramer Tavor 5-O powered speakers

Hello everbody,

I have 5 pairs of Kramer Tavor 5-O speakers that have been damaged by overvoltage (thunderstorm). The power seems to be ok. The power led ligths when they are plugged in but no sound at all. I checked the boards but i could'nt find any sign of burning or something like that.

My question is, what should i check first ? I only have a multimeter.

Thanks.

Attached are some pictures of the boards of the powered speaker.
Attached Images
File Type: jpg Tavor5Control.jpg (648.7 KB, 9 views)
File Type: jpg Tavor5side.jpg (675.1 KB, 12 views)
File Type: jpg Tavor5back.jpg (628.5 KB, 12 views)
File Type: jpg Tavor5backbottom.jpg (712.9 KB, 10 views)
File Type: jpg Tavor5backtop.jpg (786.4 KB, 11 views)
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Old 12-29-2018, 02:04 PM   #2
Khron
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Default Re: Kramer Tavor 5-O powered speakers

The physical layout could make it interesting to probe those boards.

When you say "the power led lights", does it light up green or red?

In the 4th photo, the little board on the bottom left looks like a small (independent?) flyback supply, that likely handles the stand-by side of things (and turns on the main supply upon signal detection, etc), so if the power LED comes on, either colour, that should still be ok.

For starters, you could probe the red & yellow wires on that 4-pin connection between the main power supply board and the audio board, to see if that still works. With the big capacitors on the audio board being rated for 35v, i'd expect something anything between +/-20-30v the yellow/red and ground (black wires).
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Old 12-30-2018, 08:12 AM   #3
benV
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Default Re: Kramer Tavor 5-O powered speakers

Thanks for your help Khron.

The led lights a solid green on the "On" position and if i put the switch to "Auto", it lights red if there's no input and green if i plug it in my computer audio output.

About the red & yellow wires between the main boards, here are the results :

Yellow : - 19,32v
Black : - 001,3mv
Black : - 001,3mv
Red : + 19,08v

Does that mean that the power supply is ok ?

What is the purpose of the 3 wires white cable between the audio board an the flyback supply. Is it for the "auto" mode ?

Can the overvoltage came by the audio input. All those speakers were plugged in computer in classrom but none of those computers where fried. Some others were.
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Old 12-30-2018, 09:30 AM   #4
Khron
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Default Re: Kramer Tavor 5-O powered speakers

That sounds 'round-about right then, and yes, the power supply sounds like it's fine.

That 3-wire connection may well power the signal-detection circuitry, indeed.

Next you'll want to probe the voltages on pins 4 and 11 of that 14-pin opamp on the audio board - those voltages will be coming out of the two TO-220-cased voltage regulators. I'd expect either +/-12v or +/-15v.

If that also checks out, you'll want to check voltages on pins 1, 7, 8 and 14 (expecting more or less 0v). Refer to this datasheet:
http://www.ti.com/lit/ds/symlink/tl074a.pdf

Assuming that's also all fine, then suspicions move to the amplifier chip itself. Well, unless the potentiometers themselves are still fine. I've encountered a case or two where that turned out to be the case of "no signal".
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Old 12-31-2018, 07:55 AM   #5
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Default Re: Kramer Tavor 5-O powered speakers

Pins 4 and 11 of the opamp give me - 12,9v and +12,1v
Pins 1, 7, 8 and 14 give me more or less 0v

I checked the main volume potentiometer and it's ok too.
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Old 12-31-2018, 11:36 AM   #6
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Default Re: Kramer Tavor 5-O powered speakers

Well then, that pretty much only leaves the amplifier chip itself.
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Old 12-31-2018, 01:37 PM   #7
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Default Re: Kramer Tavor 5-O powered speakers

Check resistor R20 may have popped, it looks cracked it might have fused. It is on the second power supply small PCB.
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Old 01-01-2019, 04:35 PM   #8
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Default Re: Kramer Tavor 5-O powered speakers

First of all "Happy new year" and thanks again for your help

Redwire. After you talked about the R20 resistor, i opened another pair of speaker and i looked closely the flyback supplys right bottom corners and i found what you can see on pictures sp1flybcksupp.jpg and sp2flybcksupp.jpg. I think that this is the spot where the electric arc happened !

The R20 resistor on SP1 is definitely blown. Is it enough to kill the board and completely disable the audio output ?

The auto mode on SP2 doesn't work (the led light stay red) and the board seems to be damaged around R9, R20 and Q3, Q2. Like white powder on the board,
Attached Images
File Type: jpg sp1flybcksupp.jpg (557.4 KB, 9 views)
File Type: jpg sp2flybcksupp.jpg (572.8 KB, 11 views)
File Type: jpg sp1flybcksupptop.jpg (664.5 KB, 10 views)
File Type: jpg sp2flybcksupptop.jpg (654.6 KB, 11 views)
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Old 01-02-2019, 12:59 PM   #9
benV
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Default Re: Kramer Tavor 5-O powered speakers

I pulled out the R20 resistor but it's ok. My multimeter gives me 10ohms.
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Old 01-03-2019, 02:27 PM   #10
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Default Re: Kramer Tavor 5-O powered speakers

A resistor cracked like that either got stabbed by a screwdriver, or a power surge. I would replace it.

I don't know what this little SMPS outputs, maybe 5V. It is not working?

I would check the nearby transistor as it is the part that usually fails. In the second picture, the transistor appears installed backwards? I would test Q3 and the diode as well.
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