Sontracs Univseral PSU problems/questions

[Graham]

Hey everyone, hopefully this is the right place to post this. I've been reading the board for several years now trying to absorb as much info as possible withought trying to bug the users with random, but haven't really had anything to add, just here to absorb the knowledge of the members here.

Anyway I recently acquired a Soundtracs 16-8-16 board. While everything seems to work just fine with the exception of a few latching switches that are stuck, so I can't select mic/line levels on few channels. The board has a slight noise in all chanels so it's likely time for a recap.

My main problem stems from the Sountracs Universal PSU. It's evident someone at some point did some repairs(to D12) on the unit that I don't understant. I will attach a page from the document from Tim, but will take it down asap if Tim has a problem with his docs being posted.

Anyway, for some reasons somesones fix was to afix what I assume a zener diode in series with another diode in what I imagine is the phantom supply section. It all still works, but I don't feel comfortable leaving that there when a proper diode could be afixed in place.

I will attach a picture of the area with the odd diode configuration and well as Tim's doc.(Again if Tim has a problem or another member see that I should remove it, I will do so asap).

I forgot to metion that the offending diode is D12. I had talked to my brother who was an EE in a previous life time and he suggested jst replacing both with a standard diode. I have several LN4005 diodes in stock but likely have some more values in my parts bin.

All help and suggestions will be greatly apprecieted

Cheers,
Graham

 

[RuudNL]

The 7815 is a 15 Volts voltage regulator.
D12 is added to raise the voltage to 48 V.
Maybe the phantom power voltage wasn't high enough (<48 V.), so an extra diode was added in series with D12.
In theory the diode should be a 33 V. (48-15) zener.
If you can measure the phantom power voltage and it is +48 V. (+/- 4 V) everything is OK!

 

[Graham]

Ahh that makes perfect sense! It just looked a little sketchy base on the orientation of the series diode. It looks kind of like a short time make shift repair I've done in the past.

The loaded output does in fact result in 48v(plus or minus -.3v to + .5v) the last I checked. I guess I've got some more reading to do base on zeners!

Thanks so munch for the quick and detailed reply Ruundl! If you weren't on the other side of the world I'd offer to buy you a beer as this has been rattling my head for some time. In lieu of a beer i'll make a donation to the board in your name. Or should you prefer I'd be happy to send you a group-diy t-shirt if you send me your size and location! Gotta love giving back since this would have costs me a lot of time and money on a tech bench.

Cheers!
Graham

 

[Graham]

Got this board up and running last night and it sounds fantastic! I only had a chance to run some tracks through it and monitor with headphones, but it sounds great!