Paramount - blown Schottky rectifier [resolved]

[Neuronal]

Hi all -
I have a set of Paramounts + the soft start upgrades that have been performing flawlessly for more than a year. Today, all of a sudden I heard a pop and smelled some burning (but music was still coming out). Shut it down, flipped it over, and it looks like one of the two power supply 1N5820 3A Schottky rectifiers blew (see pic attached). By inspection the rest of the rig looks fine. Should I just pop the power supply board (hints on how to do that would be welcome - it is soldered in pretty good!), and replace that part? Anything else I need to check/replace? Is there something I did wrong on install that I should look for/avoid, or is this just periodic component failure?

Thanks to all for any advice - I'm hoping I can get this back in service before folks come over for Thanksgiving

with best to all - Bob

[Paul Birkeland]

You can remove those without pulling the board (thank god!).

I did a recent rebuild of some quasi-Paramount monoblocks and ended up putting in some TO-220 style Schottky diodes, though annoyingly I didn't keep notes on which I used.

Are you running 300Bs or 2A3s in these Paramounts?  I would guess 2A3s...

[Neuronal]

I'm running 300Bs

[Neuronal]

So I should just get a couple replacement diodes, and solder them in from the top? Seems doable. Would these work?: https://www.mouser.com/ProductDetail/onsemi/1N5820G?qs=sGAEpiMZZMukxKgYRb08uPcGa8v%2FSijm

[Paul Birkeland]

For 300Bs, go for new 1N5820S, but I would caution you to also check that the 1N5818 diodes are OK too.  I would carefully pop one end of each out and verify that neither is shorted.

[Neuronal]

will do, and thanks for the advice! Am I right that I should be able to "drip" solder down from the top to attach these into the holes?

[Paul Birkeland]

There may be enough solder there already that you don't need to add more.

[Neuronal]

OK, so I replaced all 4 diodes (I used 2x 5818G and 2x5820G), see pic. A little ugly, I think. I took voltages and they are way off - B6 is 225VDC, A2 is >550VDC (and there was a strange noise when my multimeter probe touched that lead), and when I hooked onto that resistor hanging off the soft start board I got 90VDC.

Any thoughts?  I'm happy to try any suggestions, but this feels like I should send it in, maybe?

[Natural Sound]

Sorry if this is too obvious but did you make sure that none of the newly installed diode leads were touching the plate?

[Paul Birkeland]

These Schottky diodes have absolutely nothing to do with the high voltage section of the amp.

What are the voltages at pins 1-4 on the 4 pin socket?

[Neuronal]

Soooo.....feeling pretty sheepish here. It turns out I took the voltages right at start up, before the soft-start circuit kicked in (I think because I was freaked out that the PS was going to blow up from my ham-handed diode install). Turns out - the thing works just fine - voltages are right on the money if I just wait 30 seconds for all 4 LEDs to light up. Thanks, Paul, for your advice on the diode install, sorry for the false alarm....and Happy Thanksgiving everyone! I've been celebrating having a working rig by listening to the Whatnauts (best bass line ever):

[maryc27182]

I've been celebrating having a working rig by listening to the Whatnauts (best bass line ever):

Awesome tune--thanks for the link.

Mary