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EE Minimax DAC repair

Hello Gang,

Although I don't consider myself a Newbie when it comes to electronics or fiddling with technology (been doing it for over 20 years), I seem to be scratching my head as to what went wrong with my OpAmp swap. As per Doug's article, I tried the OPA2604 (dual) in U1/U2 and AD797B (single) in U6/U7 then fired up my previously working DAC. There was little or distorted output from the unit, which I then shut off, inspected interior connections, and tried again; the unit would not start up. Based on visual inspection, there does not seem to be anything obvious wrong with the unit - the fuse and power line are fine (I tried another just in case) no "leakage" or "carbon trails" on the board or otherwise.

Would anyone have suggestions as how to troubleshoot / fix this or know of a qualified / reputable repair person that can?

Thanks in advance.
daveaudiony
mofimadness's avatar
mofimadness
4,935 posts
 
I have the same exact op-amps in mine. When I first installed them, (before I repowered it up), I noticed I missed the prongs on one side of the op-amp chip. It, at first, looked perfect, but I got a little closer and saw what I did. Make sure you have all the pins pushed in and that none of them have "folded" under the chip itself.

I would pull them all back out and try again. The pins are really small and very easy to bend under or miss the holes completely, like I did.

Also make sure they are oriented the correct way.

For repair Bill at Morning Star Audio, (the importer can help).

[email protected]
daveaudiony OP
5 posts
 
Thanks Mofi,

I pulled out the chips to inspect, then made sure they were seated correctly, but no dice - I still can't get the unit to power up.

Bill had no other suggestions, either. I was hoping someone here might have more info (I think Bolder had some options for this unit at one point) or know someone who could fix....
njs
30 posts
 
Have you tried placing the stock opamps back into the EE DAC?
morganc
255 posts
 
Did you insure that you oriented the Opamps in the correct direction? Do the stock Opamps work when placed back in their original location? Did you turn the tube button off if you aren't using a tube?
daveaudiony OP
5 posts
 
NJS and Morganc - thanks for the input...

Both original OpAmps and proposed, regardless of position / orientation, do not change the outcome - unit no longer powers up.

I'm assuming this is a power thing, but can't rule out the board - anyone have wiring diagrams, specs, or similar for these?

Thanks
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