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DIY TDA1541A PCB "D3"
DIY TDA1541A PCB "D3"
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Old 15th November 2019, 12:16 PM   #401
markos4553 is offline markos4553  United States
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Location: Central, MN
The Polarity across the IV resistor does not change for AOR. The pot seems to have linear resistance from 0 to 1K on my meter.


Thanks,


Mark K.
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Old 15th November 2019, 01:59 PM   #402
markos4553 is offline markos4553  United States
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I will be unable to test further for a few days.


Thank you for the suggestions so far!



Mark K.
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Old 15th November 2019, 03:04 PM   #403
Ben Mah is online now Ben Mah  Canada
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DIY TDA1541A PCB "D3"
Hi Mark,

When you have time again, here is another test:

Remove the TDA chip and power up and measure the DC voltage across the IV resistor, positive lead to signal and negative lead to ground. Adjust the pot all the way from maximum to minimum, or vice versa. The current through the 150R IV resistor will vary. At some point current (I) should be 2mA, which is what you need. So when V=.002A x 150R = 0.30V, current is 2mA. (Ohm's Law V=I x R).

If you can get 0.30V across the 150R iV resistor, the bias circuit on the board is working properly. If not, then the 5V supply or bias circuit is probably not working properly.

Another check - power up the board with the TDA chip in place and then check the supply voltages under load. Were your previous supply voltages measured with or without chip in place?

Ben

Last edited by Ben Mah; 15th November 2019 at 03:25 PM.
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Old 15th November 2019, 11:04 PM   #404
ggetzoff is offline ggetzoff  United States
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Ben / Ryan,

Success, good voltage: -5, +5 and -15. This was after replacing: Q1, X1, X3.

Now I'm having the same problem Mark is having. With 100R across the output, I cannot zero the offset (~160mV) and I can achieve ~.23v (.002x100r) so, its close.

But, when I remove the 100R on the output, I'm at 5v output!!! The trimmer does not change this!!

What do you guys think?

Cheers,

Greg
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Old 16th November 2019, 01:49 AM   #405
Ben Mah is online now Ben Mah  Canada
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DIY TDA1541A PCB "D3"
Greg,

Are both channels behaving the same?

Are the +5, -5, -15 voltages with TDA chip in place? If without TDA chip, measure with chip in place.

Have you checked your soldering? Reflow the joints for the output bias components?

Ben
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Old 16th November 2019, 02:00 AM   #406
ggetzoff is offline ggetzoff  United States
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Quote:
Originally Posted by Ben Mah View Post
Greg,

Are both channels behaving the same?

Are the +5, -5, -15 voltages with TDA chip in place? If without TDA chip, measure with chip in place.

Have you checked your soldering? Reflow the joints for the output bias components?

Ben
Ben,

Yes, both channels the same and yes, voltages with chip in place.

I just wonder if I should replace all the bias components.

Cheers,

Greg
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Airline Pilot-If it's not Boeing I'm not going.
Aleph J, F4, DCB1, VHEX +, USSA-5, BA-3 Pre, DCG3, USSPA, Transcendent Sound Masterpiece (sold) TDA1541A D3, RH84, D3 Build guide
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Old 16th November 2019, 02:05 AM   #407
Ben Mah is online now Ben Mah  Canada
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DIY TDA1541A PCB "D3"
Greg,

First remove the TDA chip and measure the voltage across your 100R IV resistor. Adjust the pot. The voltage across the IV resistor should vary as you vary the resistance. At some point you should get 0.2V, which would indicate 2mA flowing through the resistor. This is the current you are trying to achieve to counteract the TDA's output current with no signal.

Ben
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Old 16th November 2019, 02:18 AM   #408
ggetzoff is offline ggetzoff  United States
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Ben,

I can adjust it to .23vdc without the chip installed.

It’s close....what do you think? I cannot, zero out the offset, though.
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Old 16th November 2019, 02:22 AM   #409
Ben Mah is online now Ben Mah  Canada
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When you adjust the pot, what are the maximum and minimum voltages at the pot extreme positions? Same for both channels?

Without the chip you should not get zero volts.
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Old 16th November 2019, 02:27 AM   #410
ggetzoff is offline ggetzoff  United States
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Quote:
Originally Posted by Ben Mah View Post
When you adjust the pot, what are the maximum and minimum voltages at the pot extreme positions? Same for both channels?

Without the chip you should not get zero volts.
165mv to .238 on both, almost exactly the same for each channel.
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