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Old 2nd August 2012, 10:45 PM   #81
bcmbob is offline bcmbob  United States
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Location: Bay City, Michigan
Latest checks:

Pin 1 and 11 on WM8805 read 3.28 VDC. Pin 22 still not tied but shows same continuity to those that are.

Middle LED lights with both toslink and RCA s/pdif. The switch properly selects between formats. This makes me think all the main voltages are in the proper range.

Have not purchased the Tenor module yet as I believe the other two formats should function without it. Is that correct? It is not a very expensive purchase but don't want to buy it if the problem is elsewhere.

There is no longer a ghost replica of sound. Now it is dead silent on both optical and s/pdif.

If anyone has suggestions for other points to measure please post. Also looking for good guesses about what most likely could have been fried by the first set of wrong voltages.

I'm not in panic mode and see this as one of those projects one nibbles at from time to time.
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Old 3rd August 2012, 01:15 AM   #82
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Bob,

Looking at your voltage readings in post #66 of this thread, I see that the LT7805 output voltage is 0. Have you fixed that yet?

Stick with it. This is my first USB DAC, and I will not go back to my CD player. This DAC sounds so much better to me than the CD player. I bought it thinking it would be a playground for experiments. Now I don't want to disconnect it. I'd rather just listen.
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Old 3rd August 2012, 08:14 AM   #83
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I might add that, yes, the unit should function without the Tenor module.

I think you might check electrolytic capacitors for opens and shorts caused either by reversed polarity or overvoltage. It is hard to say whether any of the ICs got fried. I think you mentioned you have test equipment to check the board for hot spots. Any changes lately?
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Old 4th August 2012, 05:03 PM   #84
bcmbob is offline bcmbob  United States
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These are the continuity paths for the LT1085 reg as I can decipher them. I swapped the two 100-220 caps thinking one might be defective but got the same readings. This is a replacement 1085 I had on hand and thought it was new but I'm ready to order a new one.

Is there anything in these photos that would affect the output of the regulator? It is still reading 13.3 in - GND - 0.0 out.
Attached Images
File Type: jpg 05Top.jpg (359.4 KB, 553 views)
File Type: jpg 05Bot.jpg (238.8 KB, 527 views)
File Type: jpg lm05a.jpg (16.0 KB, 516 views)
File Type: jpg lm05b.jpg (25.3 KB, 507 views)
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Old 5th August 2012, 07:52 AM   #85
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Bob,

It looks as if the LT1085 is being used as shown in this circuit from the datasheet, where R2 is set to 0 ohms. In that case, the given formula says the output should be 1.25V. You're not far off with 1.46 V. Note that I got the pinout confused. The WM8741 needs 5 V, not 1.46 V, so I wonder if LT1085 is the right part. Although my board uses an LM7805 in that position, the LM7805 has a different pinout, so it is not a direct substitute. I wonder if there are any 5 V, 3-terminal regulators with a pinout such that pin 1 is Gnd, pin 2 is Vout, and pin 3 is Vin. It seems that such an IC would be the right part. I would personally be tempted to fit an LM7805 but bend the pins around to match the board.
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File Type: jpg LT1085_adj.jpg (34.0 KB, 494 views)
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Old 5th August 2012, 09:28 AM   #86
regal is offline regal  United States
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Do any of these new ebay boards have software control (I2C) of the wm8741 to allow changing filters? Or is the $320 Weilang the only option for that?
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Old 5th August 2012, 11:51 AM   #87
bcmbob is offline bcmbob  United States
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I thought about substituting a LM7805 but it looks like this may be one of those version differences. The print mask clearly has the LT stamp, so it would appear the designer used it intentionally. I'm open to trying the swap if you still think it is necessary.

Also all the AVDDX pins show a range for voltage. Are there any other pins on the WM41 where 5V might show up? Don't want to be probing where I shouldn't be.
Attached Images
File Type: jpg Mask.jpg (224.5 KB, 91 views)
File Type: jpg WM41 Vo;st.jpg (76.2 KB, 94 views)
File Type: jpg WM41.jpg (65.1 KB, 152 views)
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Old 6th August 2012, 02:15 AM   #88
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These boards only have one way to change filters, and it changes the oversampling rate, too. There's a DIP switch that sets pin 22 on the WM8741 either high or low. I think you should be able to cut traces and add your own DIP switches to use hardware selection of the filter.

I did not know that Weiliang had a version that allowed software control. Interesting.

Quote:
Originally Posted by regal View Post
Do any of these new ebay boards have software control (I2C) of the wm8741 to allow changing filters? Or is the $320 Weilang the only option for that?

Last edited by dhalbakken; 6th August 2012 at 02:25 AM.
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Old 6th August 2012, 02:29 AM   #89
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Bob,

Those are the absolute maximum ratings you show from the WM8741 datasheet. Look on the next page, and you will see the recommended operating conditions and test conditions, which both show 5V as the normal analog supply voltage. I don't think there are any other pins on the IC that should read 5V--just the ones you traced out on your own board.

It is possible that your board is somehow defective being that pin 1 of the LT1085 is grounded on your board. Is there any evidence of that? Are there any resistors connected to pin 1, that should be there for normal operation?

If you're hesitant to experiment, why not drop a note to either minishow0328 or along1986090 and ask.
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Old 7th August 2012, 02:12 PM   #90
alkasar is offline alkasar  France
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FYI, LT1085 voltage regulator are confusing ! there exist in both fixed and adjustable version. A substitute for LM7805 is LT1085_fixed_5V.
LT1085-Fixed - 3A, 5A, 7.5A Low Dropout Positive Fixed Regulators - Linear Technology
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