Thursday, October 28, 2010

AMPEX AUDIO AMPLIFIER REPAIRED


The owner of this amp told me that the last moment of this amp was that he saw smoke oozing out from the amplifier and therefore I did not intend to apply power again to the amp lest I do more damage inside.

After opening the amp I went straight to test the transformer to see if it is okay…sure it has survived the ordeal.

Next I scanned around the circuit board and I noticed one component which has a catastrophic failure-as you know you don’t need to test a component with this kind of failure. Your eyes are good enough test equipment.



The two components happened to be TDA2030A: they were sharing the same heat sink so I removed them from the circuit together.

I applied power to the amp and I noticed the output voltage is still too low, the transformer is rated(13x2) therefore I was expecting around 18 vdc(13X1.414) but was too low.

So I suspected there must be another shorted component not yet picked up.

I switched off the power and touched on the components around the circuit looking for any component which is hotter than usual and I bumped on another component (i.c) which was very hot to my finger.



This must be the culprit, after checking it I found it was also a TDA2030A.

I removed it from the circuit and the voltage went up to (+-18 vdc) and I concluded that there is no more shorted component on the circuit.

The underside of the board has three darkened area where the i.c were installed which was further evidence that they must have been shorted.



I replaced the three TDA2030A and the amplifier came back to life.

Afterwards I searched for the datasheet of this i.c TDA2030A to check for its specifications and I noted that it is a 14 Watts HI-FI- audio amplifier and uses dual VCC(+-) hence why I was getting(+-18 vdc) on my meter.

I also found that it has other applications and I was particularly interested on its application as a crossover filter, a complete 3-way 60 Watt active loudspeaker system as shown in the diagram below.




I am a fun of do it yourself (D.I.Y) and this is definitely my next project thanks to Contek Microelectronics Co, Ltd.

Thank you guys

Let meet in the next class

7 comments:

  1. DEAR MR KIMATHI

    thanks for good article like always is full of fruitful points but please tell me the transformer
    was 13X2 what do you mean ? this is the winding rate of transformer between primary and secondary?
    thnx
    beh

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  2. Hi Beh, the output of the transformer was 13-0-13, means its has 3 wires on the output(secondary) the middle one is ground and therefore when you measure the output voltage with you meter set to ac range and you measure between the middle wire and any of the other two wires you will get 13 vac.

    hope i have answered your question Beh. see you and take very good care of yourself

    Humphrey

    ReplyDelete
  3. DEAR SIR

    like always your answer is clear and constructive
    than you so much
    beh

    ReplyDelete
  4. I'm still a bit confused about the transformer explanation.
    Why would any transformer be designed to deliver two identical 13VAC secondary outputs.
    Why did you expect to see +/-18VDC, you were clearly measuring the rectified & smoothed output but why?
    Was this just a shortcut, the caps surely would be a likely fault source, so why shortcut.
    I guess I am missing something.
    Anyway good article as usual - thanks always helpful & always gets me thinking.

    Peter O

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  5. Hi, take any linear tranformer and you will find that it will have 3 wire primary side and 2 or 3 wires on the secondary.

    For the primary the middle wire is used when your outlet is 110 volts but for countries using 240 volt they use the 2 outer wire... now let go to the secondary side in my case the transformer was center tap..ie the middle wire is ground, mean if you measure from this leg to any of the two wire you will get 13 vac. and if you measure between the 2 outer wires you will get 26 volts(total of 13+13)}this is still ac..now to change to dc you will need a diode to rectify and a capacitor to smooth...once this is done the voltage DC is go up by 1.414(the formula for peak voltage= rms X 1.414)

    Hope i have answered your question

    Kind regards Humphrey

    ReplyDelete
  6. Thank you so much for this very useful article i've learn a lot.
    I have also in my bench an audio amplifier the problem is the transfomer was burnt.But the problem is,there was no marking in the transformer what so ever.T he transfomer have also 3 wires in the output secondary obiously the center is the ground because its connected to both leads of 2 negative caps on 25v and the 2 wires connected to both positive leads of caps. my question is,do i get a transformer with 13X2 so that it will create an 18v? Because if i go higher than that,the 2 caps 25v will explode. I need your suggestion Sir. Thanks..

    ReplyDelete
  7. Hi there, if the main filter capacitor is rated at 25 Volts, that means the voltage on that line is 25V/2=12 Volts. this means a 12-0-12(center tap transformer is the best suited for this line.. you can also use 13-0-13 or 15-0-15 transformer without any problem.
    Regards Humphrey

    ReplyDelete