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Old 6th December 2010, 12:51 AM   #21
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Can you post some pictures of the transistors on the Placid? I am thinking you have something in the wrong spot, so pics should show labels if possible.
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Old 6th December 2010, 02:46 AM   #22
kamaths is offline kamaths  United States
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Hi glt,
I had a 5w 15ohm resistor in my parts kit. I placed it across output of placid and voltage was steady at 5.5. As suggested that resistor got very hot in few minutes.

Per Russ's suggestion,I measured the resistances across the caps in AVcc module-

C1 measured at 18k and C2 was in megaohm range. I hope measured the right ones.

Brian,

I will try to get the pictures of the transistors on placid. If I don't get clear pictures, is it OK to post the numbers on the devices?

Thanks for all the help guys, I hope I will get it up and running soon

Suresh
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Old 6th December 2010, 03:03 AM   #23
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I wasn't talking about the AVCC module, I meant on the DAC itself.

There should be no shorts registered across any of the caps at all.
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Old 6th December 2010, 03:14 AM   #24
kamaths is offline kamaths  United States
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Hello Russ,

C10, C11 and C18 measure at 16k, 15k and 15k respectively at their terminals
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Old 6th December 2010, 03:18 AM   #25
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Hi,
Can you check the power supply voltage without any connection. You found that the resistance of the Buffalo was 15k. Sometime the LM78xx do not put voltage out on less there is a load. Since the resistance is 15k and dividing 5.5 volts/15K this give you a low load. Or you can put the resistor in parallel with the Preamp and see what happen.
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Old 6th December 2010, 03:28 AM   #26
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Quote:
Originally Posted by tauro0221 View Post
Hi,
Can you check the power supply voltage without any connection. You found that the resistance of the Buffalo was 15k. Sometime the LM78xx do not put voltage out on less there is a load. Since the resistance is 15k and dividing 5.5 volts/15K this give you a low load. Or you can put the resistor in parallel with the Preamp and see what happen.
There are no LM78xx regulators involved
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Old 6th December 2010, 03:59 AM   #27
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Hi,

Oppss Still some power supply require a load to operate. Do the test with the resistor connected to the preamp. Check the output voltage.
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Old 6th December 2010, 04:19 AM   #28
glt is offline glt  United States
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Quote:
Originally Posted by kamaths View Post
Hi glt,
I had a 5w 15ohm resistor in my parts kit. I placed it across output of placid and voltage was steady at 5.5. As suggested that resistor got very hot in few minutes.
...
Suresh
That means it is almost certain the Placid is not at fault. That is how I built my Placid. After completing it, I let it sit with a resistor for many hours to make sure the supply is solid.

Try lowering the voltage of the Placid to 5V or even 4.5V. The opamp of the AVCC supply specs out at around 5.5V (if I remember correctly)
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Last edited by glt; 6th December 2010 at 04:38 AM.
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Old 6th December 2010, 12:07 PM   #29
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Was the Buffalo initially powered with more than 5.5V, say during testing of the Placid? A cooked AVCC may be causing the short. Try powering the Buffalo without the AVCC module in place and see if you get the Mute led to light.
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Old 6th December 2010, 01:00 PM   #30
kamaths is offline kamaths  United States
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Removed the AVCC module and tried powering up, none of the leds lighted up.

I was very careful on adjusting placid per instructions on initial power up as the instructions are explicit the voltage on power up can exceed 5.5 easily.

I tried adding the loading resistor per another suggestion but the problem remains
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