DIY TDA1541A PCB "D3" - Page 40

markos4553 · 15th November 2019, 02:50 AM

Hi Ben,

I really appreciate the help!

On startup Both AOR and AOL vary a bit with AOL after a little while able to be zeroed and adjusted back and forth over the 0V point. AOR settles around 90mV with one TDA and 40mV with a different known working TDA.

I realize this is very difficult to troubleshoot over the internet and I can take any measurement if needed. I can also start desoldering and replacing if necessary.

Thanks,

Mark K.

markos4553 · 15th November 2019, 02:52 AM

Voltage measurements are being taken across G and S of AOL&AOR.

ggetzoff · 15th November 2019, 02:56 AM

Quote:

Originally Posted by markos4553

Greg where was your ground reference for the voltage measurement?

Mark K.

Mark, on the chip socket GND.

Where is everyone else measuring?

Greg

ggetzoff · 15th November 2019, 02:58 AM

I measured on the socket GND for the -5, +5, and -15.

markos4553 · 15th November 2019, 03:04 AM

Quote:

Originally Posted by ggetzoff

I measured on the socket GND for the -5, +5, and -15.

Ok me too! Just curious.

Mark K.

Ben Mah · 15th November 2019, 03:15 AM

Hi Mark,

The Output bias circuit is very simple with only a few parts. If 5V is being delivered and the TDA chip is outputting 2mA, then something in the circuit is not working properly. It could be solder connections, or pot not working properly, or C56 not working properly.

You have already checked the 2K resistor. You also had measured 0.3V across the IV resistor when the 2K resistor was out of the circuit so the IV resistor and parallel capacitor are OK, and the TDA chip is sending out the 2mA current.

You can desolder the pot and test it out of circuit. You can desolder C56 and try the circuit without it. The circuit will work without the C56. Or if you have a capacitor tester, you can test it when you have the pot off the board.

Also check the solder joints again.

Ben

markos4553 · 15th November 2019, 03:47 AM

I desoldered C56 and it checked out at 1uf and I've desoldered and checked TR1 and it checks out at 1K.

I've desoldered and replaced C58 even though it tested good at 154pF. I've now tested everything in the Bias circuit so it must be somewhere else.

Mark K.

Ben Mah · 15th November 2019, 03:59 AM

Did you check TR1 to make sure that the resistance varies from 0 to 1K when you adjust it?

markos4553 · 15th November 2019, 04:11 AM

Hi Ben,

I connected one test lead to the center pin and the other test lead to the outer pins and both responded correctly. 0ohms to 1Kohms.

Thanks,

Mark K.

Ben Mah · 15th November 2019, 04:22 AM

Well, it could be that the pot is hard to adjust. 90mV amounts to .090V/150R = .0006A and 40mV amounts to .040V/150R = .000267A.

When you adjust the pot, does the voltage across the IV resistor change from negative to positive or vice versa?

15th November 2019, 02:58 AM	#394
ggetzoff diyAudio Member Join Date: Nov 2004 Location: Southwest	I measured on the socket GND for the -5, +5, and -15. __________________ 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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15th November 2019, 02:50 AM	#391
markos4553 diyAudio Member Join Date: Mar 2010 Location: Central, MN	Hi Ben, I really appreciate the help! On startup Both AOR and AOL vary a bit with AOL after a little while able to be zeroed and adjusted back and forth over the 0V point. AOR settles around 90mV with one TDA and 40mV with a different known working TDA. I realize this is very difficult to troubleshoot over the internet and I can take any measurement if needed. I can also start desoldering and replacing if necessary. Thanks, Mark K.

15th November 2019, 02:52 AM	#392
markos4553 diyAudio Member Join Date: Mar 2010 Location: Central, MN	Voltage measurements are being taken across G and S of AOL&AOR.

15th November 2019, 03:15 AM	#396
Ben Mah diyAudio Member Join Date: May 2012 Location: Vancouver	Hi Mark, The Output bias circuit is very simple with only a few parts. If 5V is being delivered and the TDA chip is outputting 2mA, then something in the circuit is not working properly. It could be solder connections, or pot not working properly, or C56 not working properly. You have already checked the 2K resistor. You also had measured 0.3V across the IV resistor when the 2K resistor was out of the circuit so the IV resistor and parallel capacitor are OK, and the TDA chip is sending out the 2mA current. You can desolder the pot and test it out of circuit. You can desolder C56 and try the circuit without it. The circuit will work without the C56. Or if you have a capacitor tester, you can test it when you have the pot off the board. Also check the solder joints again. Ben

15th November 2019, 03:47 AM	#397
markos4553 diyAudio Member Join Date: Mar 2010 Location: Central, MN	I desoldered C56 and it checked out at 1uf and I've desoldered and checked TR1 and it checks out at 1K. I've desoldered and replaced C58 even though it tested good at 154pF. I've now tested everything in the Bias circuit so it must be somewhere else. Mark K.

15th November 2019, 03:59 AM	#398
Ben Mah diyAudio Member Join Date: May 2012 Location: Vancouver	Did you check TR1 to make sure that the resistance varies from 0 to 1K when you adjust it?

15th November 2019, 04:11 AM	#399
markos4553 diyAudio Member Join Date: Mar 2010 Location: Central, MN	Hi Ben, I connected one test lead to the center pin and the other test lead to the outer pins and both responded correctly. 0ohms to 1Kohms. Thanks, Mark K.

15th November 2019, 04:22 AM	#400
Ben Mah diyAudio Member Join Date: May 2012 Location: Vancouver	Well, it could be that the pot is hard to adjust. 90mV amounts to .090V/150R = .0006A and 40mV amounts to .040V/150R = .000267A. When you adjust the pot, does the voltage across the IV resistor change from negative to positive or vice versa?