Melos Sha Gold - Schottky SiC Full Wave Rectifier Bridge

I'm very new to DIY but I hit a roadblack last night, any help or advice appreciated! The subject is an old Melos Sha Gold.

Full recap went fine, while I was there I wanted to try my hand at swapping the LV and HV rectifier bridges for modernized Schottky Silicon Carbide Diodes. I think that's what has done me in as the amp is not powering up at all right now. Bear in mind there's about 14 wires that have to be soldered/desoldered just to get the dang amp board out of the chassis! At this point I'm about to say eff it and just throw in new stock equivalent parts in hopes that I didn't blow something up already.

For reference here's an old old post about Fallen Angel implementing similar (3rd pic from the top); if you zoom in his arrangement of the diodes looks identical to what I made but the pic quality is from 2008. The stock bridges are single packages and these modern replacements are TO-220-2's hence the creative routing.

http://www.head-fi.org/t/350909/melos-maestro-modification-log-updated-oct-05-2008-large-photos

Here's what I made and pulled out of the amp last night (I tried to line up the arrangement to match the stock packaging):





To put it verbally I've got two diodes sharing pin 1 (for DC +) and two diodes sharing pin 2 (for DC -). AFAIK that's what you want in a full wave bridge rectifier. Datasheet for these Schottky's:
http://www.mouser.com/ds/2/90/3d06065a-838509.pdf

 

Looks like you soldered pin 2 of one diode to pin 1 of the other? Should be fine as long as they're soldered in accordingly... The soldered together pins would be your AC points.

 

Marv, here's an annotated version of my pics based on the ABCD conventions in the schematic shown. Did I still do it wrong then? Does to polarity of points A and C matter (lol @ the AC)? Sorry for teh n000b!

Some additional things to note based on multimeter diode test:

-The original parts when testing forward bias shows a constant resistance. (red to D, black to B)

-My diy bridges will show briefly a resistance blip across the same pins and same forward bias direction however it is not a constant resistance and goes to OL pretty quickly.

-I believe leg 1 of the schottky diodes is the cathode and leg 2 is the anode showing forward bias reading. The original bridge packages the (+) leg is the cathode and the (-) leg is the anode showing forward bias reading. The legs are equal length from the factory.

LV bridge:



HV bridge:

 

Looks good. The LV bridge has both +b and -d legs soldered to the DC terminals?

 

I believe what you are asking is if the top two and bottom two legs are shoved into the same hole on the PCB, then yes. I guess technically I could bend and join one of each of those so that only 1 leg is in the (+b) and (-d) hole of the PCB. It generally doesn't look pretty once all in.

This pic shows the tabs touching, I later separated them out and no change, also the diodes still seem to be reading forward and reverse bias so I think they survived.

 

Yeppers. Was just asking because I didn't see solder on them in your pic

The diodes look to be wired properly... As long as they're soldered in nicely, it should be good.

Also if you're trying to check resistance, go one diode at a time. Put one meter lead on the AC pin, then go to either diode with the other lead. One should conduct, one should block. Swap your meter leads and the opposite one should conduct while the opposite blocks.

Your resistance readings should basically be near zero ohms for conducting and OL or high resistance for blocking.

 

Could be something else holding me back then! Boo Next step I think is to de-solder and re-solder the transformer secondaries back on the PCB. They end up into those numbered holes on the left side of the board.

 

It can be found here:
http://www.eserviceinfo.com/downloadsm/21578/Melos_Melos Sha Gold.html

I suppose downstream DC should be going to the film cap to the right of the LV and the brown cap to the right of the HV, since I can't do this with the board installed the resistor connected to that cap will have to do maybe.

To be perfectly honest, the challenge is that my understanding of a schematic overall is probably not yet "on the level" to make a whole lot of use out of it at this point. I spent a good week poring over the document LOL!

The picture quality of the schematic is also very bad and I am not certain it is completely accurate to begin with. The drawings and parts list have been pretty helpful though. The back side of the board is a little more complicated than the drawing makes out to be as well.

These are some pics I took before digging into anything, if you look closely at the last pic you can see a black wire which goes to the - pin of the LV rectifier and a green jumper on the + pin. The 4 pads in a square just to the left is the HV rectifier.

And yes, I am well aware that this PCB design is awful on many levels and that most any modern amp today probably smokes it in any measurable aspect. Hey man I don't design these stupid things Before I decided to dig into the amp it actually sounded half decent.

 

Whoo! Thanks everyone for the input. It looks like attempt #1 blew the fuse but after cleaning everything up and reflowing the secondaries and then throwing in another fuse, I'm glad to report the amp fired right up! After removing and testing the to220 bridges I revisited bending the leads *just so* to get a nicer fitment.

This completes phase one of this project but still a bit of work ahead in stage two. Still waiting on the parts!