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Howdy, I recently purchased a Buffalo II w/IVY III, Placid & Placid BP. This unit was built for a customer in Israel by someone on the HeadFi website and the customer has been enjoying it for a number of years with no issues. Customer recently took a trip and forgot to turn the unit off while gone, so it ran for about a week. When he returned home and tried to listen to it, it was dead. I purchased it off eBay figuring I'd fix it and I'm looking forward to enjoying it! Can I get the schematic for the BII? I've rewired the primaries on the transformers for 115v and measured the output of each power supply and both appear to be fine. When the unit is powered up, only one LED on the AVCC board is lit. The other is so dim that I can just barely tell that it's trying to light. All LEDs on each PS board are lit beautifully. I loaded the Placid PS with a 20 ohm resistor to test it under load and the voltage sagged just a little 5.56 to 5.44 when loaded. If my math is right, the load should have been about 275 ma so I think the PS is working fine. When I connect PS to the DAC, the voltage drops to 1.9 vdc at the terminals so I'm guessing I have a short on the BII board. I've disconnected all wires to the board with no change. I've also removed the AVCC module, and again no change. Finally, no obvious signs of anything burnt on any of the boards. Any advice of where to look next? Also, voltages at various test points would be extremely helpful. Thanks in advance, Steve PS - I'm at my office and didn't think to take any pics before I left the house. Edited by user Tuesday, February 4, 2014 8:05:57 PM(UTC)
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I would start by testing the AVCC module by itself. 5.25VDC to IN pins. The output should be around 3.5VDC.
I would next check for shorts on the on-board regulators (I am assuming you are not using Tridents). You can remove the three ferrite beads feeding each of the supplies and add them one at a time to isolate which (if any) is causing the short, and go from there.
Once you find which supply is shorted, I would first remove the 100uF OSCON cap to see if that is the short (I have seen a few of those).
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Hi Brian,
Will do.
Are you still using the OSCON caps or have you switched to something different? What do you recommend?
What is the part number of the on-board regulators?
Is it okay to test the BII with the AVCC removed?
Finally, the AVCC is the ver 1.0 model. Do you recommend that I ad the caps to the output pins to improve stability? (have to go back and find the note that I saw while searching)
Please let me know and thanks VERY MUCH for the help!
Steve
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I switched from the Vishay/Sanyo to a UnitedChemicon model (same as I use on the Opus and such, so you can check those part lists). 100uF or 120uF is fine.
It's okay to test w/o AVCC, but you will not get any output.
The AVCC ripple thing wasn;t a constant problem, more of a confluence of part variations would cause it on occasion. That said, added stability is added stability.
The onboard regs are LT1763, 3.3V and 1.2V versions.
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Ok.
I'll report back after I check stuff further tonight.
Thank you!
Steve
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Also, you can run the DAC w/o the EL caps installed for testing.
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Originally Posted by: Brian Donegan 
The onboard regs are LT1763, 3.3V and 1.2V versions.
Brian, I looked up the regulators and I'm finding both fixed and variable models. Also, the 1.2v only comes adjustable and goes down to 1.22v as a reference voltage. Unfortunately, not finding a BOM for the BII so unable to know which part numbers are the correct ones. I was planning on purchasing from Digikey and thought I'd setup the order... I want to be sure I order the correct thing, hence why I'm asking. http://cds.linear.com/docs/en/datasheet/1763fg.pdfPlease let me know. Again, thanks for the help! Steve
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Brian, Good call on the AVCC! Definitely bad. It appears to be just the AVCC that failed. I thought that I'd tested the DAC board with and without the AVCC, but I guess I was tired and only measured current draw with the AVCC in place.  I did remove the electrolytic caps figuring I'd replace them anyway. All three on-board regs are working fine. Hopefully the AVCC didn't take the DAC chip with it when it failed but not sure how to check that. I've already ordered a new AVCC and a shirt. Would it be possible for you to include three new 100uf caps in the box and just shoot me an invoice for them? (or let me know how much and I'll just send you payment) If not, please let me know so I can get them ordered from Digikey. Just figured I'd ask if I could get them from you to save on shipping. Thanks very much for your help thus far! Steve
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