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Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 KHz

Blown OPA365 (OAVQ)

Took the plunge. Did the vref mod. First 16x caps mod from hifiduino.
Tested the dam. Works ok.

Then the other 0r, 0.1r mod.
And also the 27k4r poweron/poweroff mod.

Measured resitance after with a dmm. Seems ok.

Power on and no sound. Can connect to umanager with no problems. The dam got signal and lock but unfortunately no sound.
Late here now. Will do some more testing in a day or two..

Hi bambadoo, it's look like you have blown one of the buffer IC (next to U33 mark). Have you checked polarity of (to late now)big caps before powered?

If you are lucky you will have to replace only one buffer IC and/or -5v reg.

btw If any of you guys are thinking that all this mods are to much for you and thinking to buy a new ver2 board (Vref mod done out of the box) and willing to sale your ver1 unmodified board please PM me (only 0.01%)
thank's
Danny
 

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Check the vref voltages for starters, its the first thing I did upon poweron after performing my 16 cap mod.
Every "voltage" at J2 is ok.
However I got about 3-4mv in the vref :mad: What could be wrong? Desoldered the vref mod for one channel also. No change.

The polarity for the 16caps are ok and just as described from hifiduino site.

One good thing. The poweron/off issue is gone... Absolutely silence since nothing arrive at the output..
 
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bambadoo, for each OPA365, check that it is receiving power and that it has either +4V or -4V on its '+' input, which will indicate that the reference voltage is present.

Hi, will check later today but I suspect that the reference voltage is not present.

But I have some additional information.

When I did the mods (between the 16 cap mod which worked and the rest of the vref mod including the poweron/off 27k4r resistor mod) I also thought of soekris early post regarding the 6 main 820 uf caps.
http://www.diyaudio.com/forums/vend...magnitude-24-bit-384-khz-178.html#post4225082
If you insist to improve the onboard power supply, try replacing the 6 electrolytic capacitors with aluminum polymer types, 1000u 16V exist in same 10mm smd footprint
I have some of them on hand so of course I could make the switch.
But I did not manage to remove the original caps. I tried with one. One of the RC filter caps.
ps1.jpg

Up in the right corner. I started using a heater gun for the purpose and had to give up.
Could this be the fault? Have I toasted the cap (overheat inside) and made sure the vref voltage is not present?

If so - would really change these caps (in good manner) make it work again?

It measures approv 10.5Vdc across its terminals.
 
bambadoo, the RC caps supply the output opamps, so if you are using the raw output they shouldn't matter - that is unless they are pulling the supply down. As you are measuring 10.5Vdc, I would expect this not to be the cause of your problem.

You need to measure that you have got +/5V for the opamps, and +/-4V for the references. This will give an indication of where the problem is.
 
bambadoo,

I found one can just PULL those electrolytics off of the board. The big ones after the rectifier were especially easy.

My intention was to destroy them by pulling off the aluminum jacket and then having better access to the solder points but as I did this I found they simply came off with firm even pressure. No yanking! Pull them off in the direction of the pads so you pull against one tab at a time. Look at a spec sheet for where the solder points are, I worry an explanation within this post will not be accurate enough.

I did pull up a solder pad on the caps after the 5 volts reg but luckily it was a ground pad and is easy enough to work around.

If you do not use the balanced buffer output then you can experiment with the two furthest from the end which only affect those op-amps. If you cannot get those to come off with my "method" your board may not be as compliant as mine was.

I attempted to use a soldering iron but the pads are very difficult to touch and I worried I could do more damage to other components with the heat.

I removed all of the electrolytic caps, this way, on my board.

Worth a try?
 
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bambadoo, the RC caps supply the output opamps, so if you are using the raw output they shouldn't matter - that is unless they are pulling the supply down. As you are measuring 10.5Vdc, I would expect this not to be the cause of your problem.

You need to measure that you have got +/5V for the opamps, and +/-4V for the references. This will give an indication of where the problem is.

I can find +-/5V for the opamps. However nothing for the references. Well approx 1.5mv

Or maybe it is the 27k4 mod itself?

This little bastard here. (With a red ring) Can this be fried? I desoldered and try to "Ohm" it. Infinite. Is it a resistor or something else? It is too small for me to tell.
 

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