Thread summary and lessons learned - this added after the problem was solved.

I cooked my tridents because I inadvertently set the power from a Placid too high - perhaps 5.55 volts plus cold start-up of ~5.6v. With help from Russ I was able to repair them! Here are the lessons learned:

1) The 5.5v supply limit on the Trident op-amps should be strictly respected. They can only withstand more voltage for a couple of weeks, and there is no sonic benefit whatsoever.
2) If installing Tridents above a Legato, it is advisable to orient the boards vertically. When rotated 'sideways', they can still clear C15 on the Legato (ver. 2) and rise only a tiny bit above the AVCC board on B2.
3) The 1.2 volt VDD Trident, in particular, is key to maximizing the Buffalo II experience.
4) Thermal drift of the Placid requires attention.

Sonically, I now prefer 5.25v and Placid shunt current of 100ma.

Below is the first post of the thread
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The Tridents have sounded so fantastic for the last couple of weeks!

Then I had to leave town for 24 hours and the last person to listen did not turn off the system. 24 h. later when I returned I shut it off. The next day upon turn-on, no B2 sound. Diagnosis: Trident failure. VDD - 0 V and one LED is dark. DVCC - 2.4 V (both LEDs lit), VDD_XO - 3.30 V. Placid supply voltage was 5.50 V and shunt current was ~100ma. Heat should not be a factor: because I was concerned about internal temperatures I devised an external air replacement system that quietly vents the chassis and keeps everything much cooler than convection alone.

Any ideas concerning the probable nature of the failure and chances for repair?

Finally, any suggestions to prevent re-occurance once I get repairs or replacement boards? Would the fact that voltage started at 5.55v before brief warm-up brought it down to 5.50 be an issue?

Frank

Edited by user Thursday, May 5, 2011 11:58:31 AM(UTC)  | Reason: Not specified

Repair would be to replace the destroyed Trident.

As for prevention, It could have been a voltage spike(lighting strike or ESD). Make sure your DAC is protected from such things. Its impossible for me to say for sure. I have never seen one fail.

After turning off for a while and then back on, the output of DVCC is now up to 3.0v [new output was 3.32v]. The XO trident continues doing fine. A zap seems unlikely. The entire system including a PC is on a surge suppressor and there were no power interrupts or any other signs of trouble.

What about small but persistent overvoltage (of maybe 30-40mv) for 24 h? With a smaller-volume chassis, it has been frustrating pegging the Placids' oputput because of thermal drift. Especially with the amount of heat shed by QP1 in v. 2.0.1. If I take off the chassis top (w/ exhaust fans) it heats up rapidly, which drops the voltage. Speculation, but perhaps Placid 2.0.1 was significantly hotter than stable operating temps when I adjusted it, causing the output voltage to stabilize a little above 5.50 when the air-over cooling was in operation. Merely speculation, but possible.

OK, one last check of DVCC before posting... Yep, still 3.0v.

One other curiosity! XO trident, which is working fine, is completely shielded from Legato. DVCC trident, flaky but not dead, is horizontal over Legato but component side up. VDD trident, totally dead, is horizontal over Legato but component side DOWN. Now, I put my power and I/V resistors on the underside of Legato, but obviously the air they heat comes up each side... But the air in that vicinity should be moving much faster than convection would dictate...

Frank

Edited by user Sunday, April 10, 2011 10:17:11 PM(UTC)  | Reason: Not specified

One more question:

The plus and minus pads at the outer corners of the boards read as follows:

VDD - 1.26v
DVCC - 1.98v
VDD_XO - 1.98v

IIRC, these were at the desired output voltage when new. ...though I didn't pay close attention...

Question is, is the VDD_XO malfunctioning even though the output reading into B2 is correct? [I did order 3 op amps...]

Edited by user Monday, April 11, 2011 8:21:58 AM(UTC)  | Reason: Not specified

If anything killed the op-amps it was voltage.

You need to setup the Placid voltage so that it runs a bit low when hot, because when cool it will be higher. I usually aim for about 5.3-5.4V when hot. Down to 5V is just fine.

10-4 Russ. Just for the record, the learning is almost as fun as the listening and surely mistakes are one of the more efficient teachers! I'm now almost certain that the tridents got a 24h diet of 5.54 or 5.55 volts combined with the full force of legato's convective exhaust. Totally my fault. If the problem is just scorched op amps, it will be a rewarding 'first' for me if I can bring any of these guys back from the dead. In any case, I won't re-mount the 1.2V trident with the components facing down. Thanks for the support!

Frank

Edited by user Tuesday, April 12, 2011 2:55:51 AM(UTC)  | Reason: Not specified

Good news and bad news.

The good news is that a new op-amp has rescued the outboard 3.3v Trident. It is now putting out 3.30v.

The bad news is that the same treatment on the 1.2v Trident has changed nothing. LED2 is brighter than those on the other shunts, while LED1 remains out. I thought LEDs were pretty tough, so I wonder about those cute little transistors...

Unless there are suggestions from any of you, I guess I'll just wait until more tridents are ready for sale.

Frank

Edited by user Wednesday, April 13, 2011 10:02:36 PM(UTC)  | Reason: Not specified

It is a happy thing for a DIYer when their lovely spouse is profoundly addicted to the musical impact and fidelity that their projects have wrought. Translation: I'm ordering a few BC860AMTF!

3v lights the dark LED, so hopefully new transistors are all that is needed...

Delivery times are the issue at my house. Actual cost of the transistors is $.06!

Conversation with my wife:

Me: "Russ says we need to replace the boards."
Her: "Well they're brand new, they should be under warranty, right?"
Me: "No sweetie, it's my fault they got cooked." (...and who didn't turn the system off??? - still my fault...)
Her: "Well can you place an EMERGENCY order???"
Me: "Nnnnegative. Brian needs to make another batch."
Her: "Oh no!" ...pained, impatient, and disappointed look...
Me: "Sweetie, this is DEE EYE WYY"

Edited by user Thursday, April 14, 2011 5:26:19 PM(UTC)  | Reason: Not specified

Thanks Russ,

a) I was definitely planning on replacing both transistors ($.06 ea.!).

b) Op amp is oriented correctly.

c) Unfortunately, Digikey didn't have the transistors or I'd have ordered a few 'just in case'. ...waiting now on Mouser...

Edited by user Thursday, April 14, 2011 5:20:56 PM(UTC)  | Reason: Not specified