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
There would be a good chance that Bill O'Connell of Morninstar Audio, the Distributor of EE products, would have a competent repair facility close by if you sent the unit back. My guess is that the diagnostics would be much less time consuming, and the parts perhaps immediately available if the repair facility is tied in with Morningstar, i.e. working with them on regular basis.

If you get the unit repaired and switch to the discrete Opamps I think it will win you over despite the repair.
Hello again Al, Douglas,

Al -

No LED light. I tinkered a bit more and found that there is power coming to the board, but nothing after that (unable to trace circuits beyond taps to see where problem is). It's beginning to look like a paperweight....

Douglas -

I contacted Bill a few weeks ago about this and asked if he knew of any repair technicians that might be able to help / fix. His first response was to check power line and fuse, which I told him were fine. He then asked which OpAmps, I responded, and on his third email he stated

"...It is really hard to tell what was messed up when folks tinker with the innards of the DAC. It seems unusual that it won't even fire up. maybe a short in the power supply somewhere. Sorry I can't be of more help."

So regardless of the problem, it seems there is no one available to fix this unit, which is unfortunate. It looks like I won't be able to try those discrete Opamps you speak of.

Thank you.
I just sent Bill a link to this thread. I'm sure he can clear up the confusion.
Sorry to hear that, Dave. I still think it would be worthwhile, though, to order replacements for the parts in inexpensive form, and give them a try. Per Doug's articles the LME49710 and LME49720 should be suitable, and can be ordered from Digikey for a total of not much more than $10 for the 4 parts:

LME49710 (for U6 and U7)

LME49720 (for U1 and U2)

Hope that helps.

-- Al
I'm just not sure what I can do for you. Tech repair is expensive,time and trouble shooting to find what went wrong in your op-amp swap. Then replacement parts and putting it all back together.

I have a couple new in box older DAC's not the DAC PLUS that I could let you have for my cost.Probably would cost about the same as doing a repair or a few dollars more. As I saved a couple of these just in case something went wrong with somebody's original DAC if my customers. It is an original DAC correct? Have to ask, did you purchase from me or second hand? Let me install the Dexa's though if considering throwing them in yourself.

Hope that helps,
Bill