Trying to repair an audio amplifier

Thread Starter

GoldMember

Joined Aug 1, 2020
8
Hi all. My computer speakers have stopped working. Grandlab M-333. It's a cheap, little subwoofer with an amp inside and 2 satellite speakers. They sound great and I'd like to learn more about repair. l've replaced the (3) burned TDA2030A's, (2) 3300uf 25V caps, and I now think there's no output from the transformer. I should see 13v between each blue wire and the black (outputs), true? I've got 120v AC in and 0 AC out. The power switch seems to have fried "ON", by the way.

If so, can you guys help me find this transformer or a suitable replacement? I've had no luck. The numbers on it are SY-57A13110D02. I/P 120V~60Hz. O/P 13VX2~1.1A.

Thanks! And if you can recommend anything else to replace or check I'd much appreciate it. I assume that the transformer failed and took out the other stuff. ? It has a strong "burned electronics" smell inside. I've attached a few photos.IMG_20200801_084943_2.jpgIMG_20200802_074717.jpgIMG_20200802_074651.jpg
 

Dodgydave

Joined Jun 22, 2012
9,453
Assuming you're correct there should be AC between the Blues and Black is the Centre tap, possibly the bridge rectifier diodes are gone too, the Tda2030 is a terrible amp chip, you can replace the transformer with any 13-0-13 type current rated, personally I would rebuild it with a premade amp module of a better quality stereo chip like TDA7297.
 
Last edited:

Thread Starter

GoldMember

Joined Aug 1, 2020
8
Hi, thanks for the response. I have nothing between the blue wires. Is there anything to measure regarding the center tap? Are the bridge rectifier diodes, right next to the power wire inputs on the board?

Thank you for your recommendation of a better amp chip. I would like a better one but can't afford the time to redesign now.
Would this transformer work?

https://www.ebay.com/itm/NEW-Philmore-120VAC-to-24VAC-1000mA-1A-Center-Tap-Power-Transformer-12V-0-12V/274346839319?epid=1203572058&_trkparms=ispr=1&hash=item3fe0588d17:g:fKcAAOSwJjteo2s~&enc=AQAFAAACcBaobrjLl8XobRIiIML1V4Imu/n+zU5L90Z278x5ickkY3FSd4Ad8xn3oRtkVexxrIrasemdhfIW3AKedIdg6MoSnjDwizUO0U54tKjCT3mEaV7ERK/Y1HqksWxd+Dl0FuAWWwOUiUnFluIlBqer/ltL/0PTnuypvtcXXyFlFxykxGIKBL4/Rs+n9bwPxBUmcBGZdc/PRtvbZ2Xb57MCUOsbx64J2XvxtjIiW4SzAxsATlpLyr2eeeC5Nu8w4zBhL4u38zPvHol79uVmSDCrmv+z7Ty9yidXKFmfwcIzUtHCtggZxXsqs2/IMBmMdpYWX9nEOiawfFB5uH0qmcTe6ThXqeX1f/SnHgbKty/9axcBBwNUXRlePgu/+SsVdGnN/ZIa7ESapejaQcZiwIHI1ScmzB4Y9jzfMNDNjrzBXrROhTcB61UeLD6DzBXc5BldwKrdXnWcWw7MPrriZDsiyhpIP9u89UlRfX7wm0p8rz1L5WoFZwS/lSHmxWQv7Lboj/KnZESiU0r4usrqYQzIA0z6AfmGWDR9FL0D8fO928DRUaAHKGB4uNFoLQUPfHEBwJpMgr4FPQGT9XYLAqaDbm6PlKof3fMzp6JkGRVr41QJsboc/lk6OLLsvx3DgiaxEq9R7vdQ/BBfkm/m48WIfsZi6yKJ9lBkN30vbMm37SKTg7rMxgpNQUhkSJwSefuVJI71wOEuN1pOnWV4gvT4vLd3sxi0DKzMKAZsUj+Mpa/siBUnbfxvYIqvGdunqnATuDtmBpAgLjF0tsKgnY6f9MApjzvBWYGKTJUdLWR17YCvnWMOqiq+L7nQ2Nx8tqKwCw==&checksum=2743468393193e99abe958784e69810cec0234fdfbcf

Is it close enough? Is there a better site to look for one? I can find nothing online in 13v-0-13v.

Thanks again for any help.
 

RduC

Joined Nov 21, 2018
1
Hi, thanks for the response. I have nothing between the blue wires. Is there anything to measure regarding the center tap? Are the bridge rectifier diodes, right next to the power wire inputs on the board?

Thank you for your recommendation of a better amp chip. I would like a better one but can't afford the time to redesign now.
Would this transformer work?

https://www.ebay.com/itm/NEW-Philmore-120VAC-to-24VAC-1000mA-1A-Center-Tap-Power-Transformer-12V-0-12V/274346839319?epid=1203572058&_trkparms=ispr=1&hash=item3fe0588d17:g:fKcAAOSwJjteo2s~&enc=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&checksum=2743468393193e99abe958784e69810cec0234fdfbcf

Is it close enough? Is there a better site to look for one? I can find nothing online in 13v-0-13v.

Thanks again for any help.
You measure no secondary voltage. Check for secondary and primary continuity. If open , or the primary and secondary are shorted together then a destroyed transformer is confirmed.
 

Deltatango

Joined Apr 16, 2012
12
My line of thought would be the transformer has a thermal fuse in its primary side which can be found and replaced if you take care, transformers are "pretty tough" if large enough to cope with faults like yours. A multimeter on ohms will verify a resistance between its secondary wires but open circuit on the primary which is what I would expect, if you can replace that fuse I would then fire it up disconnected from the board and see what happens, if that fuse goes again then its primary is damaged so faulty otherwise you will find voltage on its output side.

Now unless you are lucky to get an "odd" 13 volt transformer I would opt for a 12v version but at double the amperage this will mean it will drop less voltage when under loading and be nearer what you want.

I would meter those rectifiers on high ohms reverse to see if any are leaking or better still change them for at least twice their voltage rating.

Hope this helps you ......

David
 

Dodgydave

Joined Jun 22, 2012
9,453
Hi, thanks for the response. I have nothing between the blue wires. Is there anything to measure regarding the center tap? Are the bridge rectifier diodes, right next to the power wire inputs on the board?

Thank you for your recommendation of a better amp chip. I would like a better one but can't afford the time to redesign now.
Would this transformer work?

https://www.ebay.com/itm/NEW-Philmore-120VAC-to-24VAC-1000mA-1A-Center-Tap-Power-Transformer-12V-0-12V/274346839319?epid=1203572058&_trkparms=ispr=1&hash=item3fe0588d17:g:fKcAAOSwJjteo2s~&enc=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&checksum=2743468393193e99abe958784e69810cec0234fdfbcf

Is it close enough? Is there a better site to look for one? I can find nothing online in 13v-0-13v.

Thanks again for any help.
Yes go with a 24V ct Transformer, but measure the resistance of the primary and secondary windings first to see if it's open circuit.

The Diodes are the 4 Black with a Silver stripe components next to the Blue wires.
 

Thread Starter

GoldMember

Joined Aug 1, 2020
8
Hi all. Thanks so much for helping.
@Deltatango Ohms across the brown wires is open and 1.7 ohms across the blue wires. That's what you expected. Is 1.7 in the ballpark for the blues (secondary)? I also get .9 ohm between each of the blues and the black (center tap). Ok?
@Ylli, Yes, AC volts across the blue wires shows nothing while 120v is applied to the brown wires.
Can I test the diodes in circuit or do I need to remove them? How to test?
@Deltatango Should I just start taking the transformer apart to find the fuse??

Thanks!
 

Ylli

Joined Nov 13, 2015
978
Also, what is in here:
Annotation 2020-08-02 171840.png


And where are you connecting your ohmmeter when you are trying to measure the transformer primary resistance? If you are looking across the AC power plug prongs, then you also need to be sure the fuse and whatever is under that shrink tubing is OK.
 

Thread Starter

GoldMember

Joined Aug 1, 2020
8
Also, what is in here:
Annotation 2020-08-02 171840.png


And where are you connecting your ohmmeter when you are trying to measure the transformer primary resistance? If you are looking across the AC power plug prongs, then you also need to be sure the fuse and whatever is under that shrink tubing is OK.
@Ylli Sorry, I meant to answer this. It's just a crimp connector.
I am measuring directly on the transformer now.

Guys, can I just get this and be done, instead of disassembling/reassembling the transformer? It's double the amps as suggested.
https://www.ebay.com/itm/110-220VAC-to-24VAC-2000mA-2A-Center-Tap-Power-Transformer-12V-0-12V-24VAC-12Vx2/124225523209?hash=item1cec6b0e09:g:CgkAAOSwB4Je6TNw
 

Dodgydave

Joined Jun 22, 2012
9,453

Thread Starter

GoldMember

Joined Aug 1, 2020
8
I picked up this transformer at MarVac in Costa Mesa. It's 12v-012v at 2 amps (almost double amperage). Ok?
I also got new diodes but MarVac couldn't find ones that were twice the amperage (per suggestion), just direct cross references. How do I check ones that are in there? Can I check them in circuit? Or should I just change them? Please see the pics.
Thanks again for all of the help!IMG_20200803_182035.jpgIMG_20200803_183131.jpg
 

Dodgydave

Joined Jun 22, 2012
9,453
I would just replace them, to test them put your Dvm on Diode Test, and put the Black lead on the Cathode (silver stripe) Red lead to Anode, it should give a reading of 0.7 V approx , reverse the leads and it should be open circuit.
You can test them in circuit.
 

Thread Starter

GoldMember

Joined Aug 1, 2020
8
@Dodgydave In circuit, they test between .53 and .55. When I reverse, them meter climbs a bit. Not open but maybe because they're in circuit? Open on my meter shows 3.147. I think I'll just replace them. Thank you!

Do you guys approve of the transformer I got? It's not exact. As long as I have a reasonable chance of it working, I'll try it.
 

Deltatango

Joined Apr 16, 2012
12
You seem to be winning, as for checking diodes in a power supply supplied by a transformer my favourite method would be to use an analogue meter with a 9v battery for the high resistance range this will help identify reverse leakage in a weakened diode, with low ohms for forward, I found that under low ohms forward, its high test current warms them to show up junction issues, beware that lowest forward current on a meter may exceed a small diodes capacity so always check.
The "high" voltage puts them under a small reverse stress so if you see a needle move under a reverse check, I would then warm it by putting an iron near by it you should then see that resistance fall, thus one duff diode.
For checking diodes in a bridge formation I will always disconnect 3 points feeding it, transformer for sure plus either its + or - terminal or you will measure "leakage" as a result of circuit components or capacitors, on a 4 diode set up I would unsolder and isolate one leg of each diode.
An old diode standby would be 1N5008 3A 1,000V in your circuit it will never fail! though you can use 1N500x at least a 100v version or greater.
You do not have to fit more powerful diodes as long as the fuse system covers those original type diodes the higher current transformer was to provide a little more voltage than 12v, this is due to loading effects that will lower a transformers output.
So in your issue a slightly heavier transformer will give out a higher voltage under lighter loading of your circuit.

Hope this helps and provide a little more insight...........

David
 

Thread Starter

GoldMember

Joined Aug 1, 2020
8
@Deltatango Thanks so much for your detailed response. I replaced those diodes and the originals tested good with my digital meter on diode check mode.
I did seem to be winning... I turned it on tonight and heard sound come out. It was great for a second until I realized that it's distorted. It doesn't sound good. I need to do some more listening but it seems like the left channel is worse than the right. I will listen more and report back. Either it's the "replacement" transformer (I don't think so), or some other part(s) that got ruined when the thing blew. What else in this simple amp can/should I check/replace?
I sincerely appreciate all of the responses here. Talk soon.
 
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