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Old 1st June 2009, 12:13 PM   #321
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Quote:
Originally posted by col
have you attached a LED to the fault pin? Is the light on when the amp is unmuted?

edit: try touching the fault pin to the unmute. That should reset it.

col.
When I had the led and resistor wired up to the fault pin, it did not light up at all, which makes me thing the output section is good. I've checked the output diodes and they are ok along with the inductors and they appear to be ok.

I'll try touching the fault it to the mute pin and see if that does anything.
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Old 1st June 2009, 12:28 PM   #322
col is offline col  Australia
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when you had the led on the fault pin did it light up when you muted the amp?

Maybe try inputing a signal directly to the IC pins.
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Old 1st June 2009, 01:17 PM   #323
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Quote:
Originally posted by col
when you had the led on the fault pin did it light up when you muted the amp?

Maybe try inputing a signal directly to the IC pins.
Turns out the LED I was using wasn't working, I've now wired up a working red LED and it now lights up when unmuted when wired up to the fault pin which makes more sense.

When the amp is muted the LED is no longer lit... Basically the Fault LeD only comes on when it the amp is unmuted.

I'll try inputting the signal straight to pins 10 and 13, and see if that works at all.
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Old 1st June 2009, 02:54 PM   #324
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I think the TA2020 must be dead, but at least I have learned a little about how the amp works.

It turn out the zener diode from the fault pin goes to the mute pin, so at stock this amp has overcurrent limiting disabled. I'm not really sure why they use a zener instead of a normal connection, but I found when I had my fault LED working I could short the mute pin to the fault pin and the all familiar clicking would return.

I think I will remove the zener between the mute and fault pins on my next lepai to arrive as I think overcurrent protection my have saved the tripath IC in this case...

As the fault LED was coming on all the time I was thinking it's probably one of the outputs shorting, and true enough it was!

I pulled out the output diodes and output inductors, and measured the resistance from the outputs from the Tripath IC to ground, and I found that 3 of the outputs had a resistance of around 40kR to ground, while the other input was a short to ground.

I thought it could be a bridged PCB track so I desoldered the pin and pulled it from the PCB, and yet there seems to be a short thru the Tripath IC! I guess something burned thru within the IC...

Still, my next Lepai should be here in a few days, I'll try and be a little more careful with my next one, and I've always got this one for spares...

Thanks for you help col, I didn't have a clue where to start before but I'm now pretty familiar with the TA2020.
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Old 1st June 2009, 11:00 PM   #325
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It must have been too hard to implement the overshoot diodes on a one-sided PCB, so they left them out. I don't see the logic behind it being a cost cutting measure when it obviously puts the chip at risk operating at voltages above 13.5v especially, if they have disabled the over voltage feature :|

I think the LM338T 5A regulator circuit before the power input is the way to go. That way you can connect it to any DC voltage from 32v down. Just remember that it requires the voltage to be at least 1.5v above what you want to operate at for regulation to work.

here is the data sheet:

http://pdf1.alldatasheet.net/datashe...SC/LM338T.html

I based my circuit on "FIGURE 3. Regulator with Protection Diodes". The caps I'm using are much bigger than the diagram and the one after the regulator is low ESR. The power is very clean.

http://pix.minirig.org.au/main.php?g2_itemId=1057

With the trimmer you can adjust the output voltage to what ever is desired. Iv'e got mine set on 13.3v.

col.
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Old 2nd June 2009, 12:05 PM   #326
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Default Re: Bulk capacitor

Quote:
Originally posted by Calamaro
I think it would be very useful to replace bulk capacitor (180uF: TA2020 schematics have two x 180uF, someone goes up to 1000uF, I noticed that two x 470uF give better mids...). Any experience?

Hi Calamaro,


Do you mean that I should change the 180uf cap and metal cap in pair as attached photo?


Thank you.
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Old 2nd June 2009, 08:01 PM   #327
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I apologize for my delay in answering, but in Italy we had a long weekend due to the bank holiday of today, so I went out of town for a little break

cheric:
if you did the bypass mods you must replace input resistor, 20/22k will works fine.
As explained by Gmorris and Buckapound, input capacitors form a high pass filter with input resistor so go over 1 uF. Datasheet suggests 2.2uf, on the Bay you can easily find some mkt small enough to fit in the amp case. Ero 1822 is a very good cap, MKC dielectric is polycarbonate that is regarded to be much better, as good as polypropylene.

aszu:
further improvement can be done replacing bulk capacitor and output inductors (see Col experience), and adding some capacitance to 5v side (I did it on another pcb so I have to study a little bit this board to see how to do it on Lepai. I'll be back soon ).

panda360:
no, just replace capacitors pointed by the arrow (one electrolitic and one ceramic, please see pict.). As electrolitic replacement Tripath suggests Panasonic FC or HFQ, but I think anything will be better than the existant one! Anyway go for a low ESR and add some capacitance (470uf or even more). Replacement will be more confortable if you invert electrolitic and ceramic cap place (they are paralleled), as ceramic has more room on the board, but pay attention to electrolitic polarity! Plus on chip side, minus on pots side.
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Old 2nd June 2009, 09:14 PM   #328
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Calamaro,

Many thanks. I will swap out the MKT 1822 for the MKC 1862.
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Old 2nd June 2009, 09:16 PM   #329
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Please let me know.

ps.: you have my vote for the best biography on the forum.
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Old 3rd June 2009, 12:15 AM   #330
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Default 100nF monolithic bypass on the opamp rails

For those that have kept their opamp in the circuit a minor mod but well worth doing is bypassing the opamp power rails.

http://pix.minirig.org.au/main.php?g2_itemId=1063

Best caps for this purpose are 50V 100nF monolithic, these are designed for bypass applications. Polyester caps can be used for bypassing but they are not as effective at very high frequencies.

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