Amplifier / power supply Help

[edb1984]

Hello All;
(please forgive any ignorance or stupidity in this post as i am just a very basic amateur at electronics)
i recently purchased a self powered (integrated amplifier) Q Acoustics sub-woofer.

i bought it knowing it was faulty but not knowing what was wrong with it apart from it blew fuses, the guy i got it from had bought it a month prior from another guy selling it as faulty.

i tracked down the original guy before i bought it and he said his son had switched it to 110V and it popped, the "magic smoke" came out the back and from then on it blew fuses.

anyway long story short - i was hoping to get my hands on it and with my limited knowledge be able to replace a few components on the board or just stick in another power transformer for the amp. i have repaired a few TV's and old Tape decks in the past and the power side has been quite easy to troubleshoot and fix with my very limited knowledge.

my problem?

it appears the guy who i got it off has had a stab at working out what was wrong with it and made a bit of a mess - also the power and amplifier are all on the same board so i cant just swap it all out for a fresh one without replacing the amplifier.

see below for some pictures of the offending board - notice the black soldered on fuse, and the marks on the rear of the board where he has attempted to de-solder a d13009k , then bridged a few pins with excess solder then turned it on. and i think he has tried to turn it on without the heat-sink attached because the d13009k were so black with smoke that i had to wipe them clean but the heat sink that was posted with it was perfect, no signs of burns or smoke around the thermal paste marks where they were mounted.

(what i have tested so far)
i have had a poke around with my meter and components are measuring as expected, visually the amplifier side is good, nothing looks like it has gotten hot or damaged, all the damage appears to be smoke/heat on the power side.

my questions are as follows;
"i cant find a schematic for the board"

(1) Is it worth trying to repair? or do you think it would be possible to bypass the power supply side, buy a new power supply, and tap it into the amplifier side? (speakers and everything else is good, including the crossovers etc and the price of this speaker is approximately £270 so i dont mind spending a little to fix it as i only paid £35 including postage) 

Supposing its worth a try to fix;
(2) Where can i find another two d13009k ? i cant find any available - can they be changed for another equivalent?

(3) The ceramic capacitor next to the transformer has "Exploded" how will i find the value to replace?

(4) any advice on repairing it? is it worth taking the transformers out and testing them with my meter out of circuit etc etc?

here are some photos

[jaxbird]

Most certainly a power supply with a missing heatsink and a blown transistor   

You'll need to figure out what caused the transistor to blow.

http://www.datasheet-pdf.com/datasheet/ETC/542996/D13009K.pdf.html

[edb1984]

i thought it might have been that it has been switched to 110, then blown the fuse on the board and by the looks of the internal fuse it looks like a higher rating than the others that were in the "box" of components sent so i dont know if the next guy that had it swapped out the fuse and turned it on not noticing it was on 110v, then decided to solder in a higher rated fuse and its not cut out at the rite point and blown a few parts - although i can think of why he would of removed the heatsink?
(it also looks like he may have tried to bypass the fuse because there are two bits of wire soldered to the fuse that have been cut??)

[jaxbird]

I recently did a successful switchmode PSU repair (I'm not an expert in this area) but I think you will get some useful advise from reading this thread:

https://www.eevblog.com/forum/projects/failed-24v-switchmode-psu/msg453070/#msg453070

[mariush]

Those transistors are pretty much generic, just search for 13009 on digikey or farnell and you'll find them made by lots of companies. Get a pair with decent specs and you're set... example: http://www.digikey.com/product-search/en/discrete-semiconductor-products/transistors-bjt-single/1376376?k=13009

I don't know the resistor value BUT... the whole board is pretty much an ATX power supply based on an old design, very common.  Most such power supplies used 13007 or 13009.. typical of 200-300w power supplies.
You can google for some schematics using 13009 and you'll find easily some and then you could just look and see if the design matches yours more or less - see if the design uses same value for that resistor as another resistor on the board for example, in that case you could measure that other resistor you know what to use.
For example, here's a site found on first google search page: http://320volt.com/en/guc-kaynagi-semalari/  and this is a schematic from this page with 13009 : http://320volt.com/wp-content/uploads/2011/05/300w-atx-sg6105-ei33-ee16-ee19-2nc60-mje13009.png

Your board is just a power supply without the atx connector and extra -5v or -12v, it just outputs a 5v for the electronics aand another voltage, probably for the amplifier.  If you look in the first picture, you have the AC input connector on the bottom right, you have 220/119 switch header on the right center, and you have a 4 pin connector on the bottom left which is basically  5v standby , ground and a pin CON which I suspect is the power on pin (connect to ground and psu starts).

There's also a header by the two black capacitors which I suspect is the output voltage for the amplifier and that's where it may be a bit tricky... it could be a split power supply design, one pin could be -v or something like that, one ground and one +v  - center pin looks to be ground because of the capacitor negative strip pointing to that trace.  You could get some idea about the output voltage on those pins by looking at the capacitors and their voltage rating - if they're 16v rated, you probably have a plain 12v power supply. Another way to get the voltage would be to look at the TL494 and the resistors near it - a few resistors are used as a voltage divider and tl494 acts as an overvoltage protection - if voltage goes too high on one of the outputs then the input voltage after the voltage divider is too big, so the tl494 kills the power supply.

If it's not split power supply and the output voltage is 12v, then you could basically buy any atx power supply and cut the wires and just leave a few 5v and 12v .. this would be a typical psu using 13007 or 13009: http://www.newegg.com/Product/Product.aspx?Item=N82E16817170014

[edb1984]

also a header by the two black capacitors which I suspect is the output voltage for the amplifier and that's where it may be a bit tricky... it could be a split power supply design, one pin could be -v or something like that, one ground and one +v  - center pin looks to be ground because of the capacitor negative strip pointing to that trace.  You could get some idea about the output voltage on those pins by looking at the capacitors and their voltage rating - if they're 16v rated, you probably have a plain 12v power supply. Another way to get the voltage would be to look at the TL494 and the resistors near it - a few resistors are used as a voltage divider and tl494 acts as an overvoltage protection - if voltage goes too high on one of the outputs then the input voltage after the voltage divider is too big, so the tl494 kills the power supply.

WOW, Thanks for such a detailed explanation - you are a superstar.

Can you please help a little more? - i have checked out those schematics you linked and also checked a few more but cant find much that matches - especially on the trace for the capacitor i want to replace so i think i need a new supply.

looking into it, the three pins next to the black caps are as you suspected, middle ground and the caps are 1000uf @50v (so maybe not a 12v?)

as to the tl494 and resistor values - to save listing the values pin by pin I have taken a close up photo of the rear


if you can let me know what voltage supply would be needed then that would-be great.

the other outputs on the board that go to the amp are listed as  +5v / GND2 / GND2 / PCON     and then the three pin connector you have previously mentioned - the wire on that is colour coded (red / black / white).
unfortunately the amp board is multi layer and has no markings so i cant work out much from that

[mariush]

I actually can't see that blown resistor, as much as I try.
Yes, it's probably not 12v if the capacitors are rated for 50v.  is there some text around the connector on the amplifier board that could tell you if it's +V and -V, or that could tell you the voltages? 
If you want to continue and try to fix that, I would suggest replacing the fuse and the two 13009 and the resistor (but i don't see it) and see if that solves it. (if you want, you can put a incandescent lightbulb in series with the mains as a current limit, to protect

Those TO-220 ICs on the heatsink what does it say on them? If they say something like MBR20100... those numbers tell you it's a diode rated for maximum 20A , 100v - that could tell you voltage is below 100v (usually much lower) and the power supply outputs less than 20A - doesn't get you much closer to figuring the output voltage but it's something.
It would be somewhat useful to figure out the wattage of the power supply, but you can also do this by looking at the label in the back of the speaker where it says 220v 0.5A or something like that - that would mean 100w power supply (220*0.5a = 110w), or you could look at the specs of the speaker on the website and if it says maximum 75w or something like that you should estimate a 100w psu due to the amplifier efficiency.

Are the wires colored differently in the cable going to amplifier board? That's a hint (but not always, not reliable) that you have -v and +v.
Can you see on the amplifier board what amplifier chip is used? Post some pictures of the boards and write down what it says on the ICs on that amplifier board. Some ICs have datasheets available, so you can figure out the maximum input voltage of that amplifier chip and determine the power supply from there. Some datasheets even have basic circuit examples showing how the chip is connected with single power supply or with -v and +v so you may get a clue from there about what power the amplifier board expects.

edit: ah I see you pm'ed with TDA8920 : that needs at least +/- 12.5v , typically +/-27v, maxim  +/- 30v.  The power supply probably outputs +/- 24v.

I'm not sure where you'll find a power supply with positive and negative voltages cheaply. Maybe you can find one with two separate 24v outputs or get 2  24v power supplies and connect the + of one to - of one and get your virtual ground that way.

Alternatively, you can get a 36v transformer with center tap rated for about 100VA or more and build one :



You'd need quite a bit of capacitance on each +v and -v, that's why there's 2 caps on each side. I would go with at least 10.000 uF on each side, so maybe 1 x10000uF 35/50v or  2 x 8200uF 35v or 50v on each side.

Something like this would work: http://uk.farnell.com/pro-power/ctfcs100-18u/transformer-100va-2-x-18v/dp/1780897 (not sure where you are, you don't say the country)

If you go this route, make sure you connect -v and +v where they should be... you can follow the traces on the amplifier board to the power connector to see where -v and +v go.  Or just put your multimeter in continuity mode, put a probe on the tda chip on the pin for POSITIVE power supply and then on the pins of that connector, and you figure out the positive pin. Same for negative and ground.  The pins for tda chip are in the datasheet.
And you'd also need that 5v which you can probably get from a basic wallwart or phone charger.

[wraper]

That D13009 is yet another clone of the MJE13009 which is very common part, BTW check red film capacitor, they fail quiet often.

[edb1984]

humm, i have just got home from work and dont have time to probe the amp board but i will in the morning and update with results -

how about this board? i have been searching all day on and off at work for power supply's and i came across this;
http://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&langpair=fr%7Cen&rurl=translate.google.com&u=http://www.audiophonics.fr/smps300re-module-dalimentation-decoupage-300w-24v-p-6795.html%3FosCsid%3D0778ab92de8dceb9e90838fb817b801a&usg=ALkJrhj2veDCk5zkbz6qNAU6YMabVW6jVA

data sheet here
http://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&langpair=fr%7Cen&rurl=translate.google.com&u=http://www.audiophonics.fr/images2/6189/SMPS300R.pdf&usg=ALkJrhjkZtv2mhvzfeV_FycvmN92eyrxhw

or here is a full list of their boards
http://translate.google.com/translate?u=http%3A%2F%2Fwww.audiophonics.fr%2F&langpair=fr%7Cen&hl=en&ie=UTF8

do you think this would work? - also it has a auxiluary voltage output, could this be used with a step down converter to supply the 5v output?

Thanks again everyone for all the help 

[edb1984]

UPDATE! - i have just desoldered the caps around the voltage output and scraped off the black "glue" covering everything and the are marked +27 / GND / -27 - so now i know the voltage output.

I actually can't see that blown resistor, as much as I try.

see picture below

Those TO-220 ICs on the heatsink what does it say on them?

one is dec 0409
other two side by side are stth1002c gkobn  vu chn 929 (i think, i have had to scrape silicone off them and they are hard to read)

It would be somewhat useful to figure out the wattage of the power supply

140 watts (combined power output from twin mono class-D power amplifiers)
Another website says 150 watts
says 100 watts on the back of the sub-woofer housing

Are the wires colored differently in the cable going to amplifier board?

red -27v black gnd white +27v

Can you see on the amplifier board what amplifier chip is used? Post some pictures of the boards and write down what it says on the ICs on that amplifier board.

Photos below,


chips are [TDA8920BTH] and a  [ADAU1701 JSTZ 0933 F], then two smaller chips that i cant read without getting my magnifying glass (they look like EPROMS on a TV board i repaired a few weeks back)
no other markings of voltage or inputs

sorry to be such a nag asking so many questions - i hope i am being helpfull enough with my descriptions to identify the power board needed

Thanks Again!

[mariush]

Excellent. You can use that power supply you linked to, which gives +24v and -24v, or you could build a power supply cheaper like I said with transformer and large capacitors.   The second option will be cheaper than 60 euro   even if you go with a transformer bigger than 100va but it requires some soldering and some do-it-yourself stuff. It will also be heavier and take up more space but there should be enough space inside the subwoofer.

The 5v usage will be very small, under 1A .. basically maybe 100-150mA for the ADAU chip (which is a dsp, works at 3.3v produced by that linear regulator VR401. So like i said, you can probably use a small 5v adapter or usb charger (just cut the jack and you have black wire ground, red wire 5v.

140 watts (combined power output from twin mono class-D power amplifiers)
Another website says 150 watts
says 100 watts on the back of the sub-woofer housing

Yeah, since it's a subwoofer i assume it's only one big 8 ohm speaker and then the tda is in BTL configuration (both channels are linked together as 1 output) ... if you go in datasheet at page 14, you see there 36w per channel at 8 ohm with thd 0.5%, so realistically that subwoofer would be maximum 72-80w of audio power. But to do that, you'd need maybe 150-200w at the power supply, as the amplifier is not 100% efficient.
You don't need exactly +/- 27v, with +/-24v you're just going to have a bit less maximum output if you lower it, which you won't notice unless you turn the woofer to the maximum (and even then you probably won't notice anything)

ps.. for the amount they charge and the "reviews" on hi-fi sites, they sure have a very disappointing power supply. Like they went shopping for a "just good enough" power supply, instead of paying a few dollars more for a Delta or some other brand name power supply.

[Shredhead]

Man, I hate to be a downer but that amp isn't worth the part cost to fix IMO.  I would check the output transistors before putting any $ into the PSU. 

Parts-express has some pretty cheap amps around the same specs for probably the same cost as the parts would be to fix yours.  Or you can double your amp for not very much more money (you are powering a subwoofer after all).  Rating an amp at .5% THD is a clue to me that they are lying out their ass about the wattage.

[Shredhead]

They sell digital amp boards without PSU's, plate amps, and Pyle stand alone small amplifiers all as cheap as you can get.