Nemesis NC210 blown transformer help!

Duc · #1 10-05-2010, 10:08 AM

Hello!

I am into electronics repair and I have a friend's Eden NC-210 that blows fuses. Verdict is that internal main transformer is shorted. All I wanna know are outputs voltage ratings of it to get a replacement. Must be 2 x 25Volts or something but I can't be sure since there is nothing anywhere that mentions although I searched the whole web too... If someone (owner) has some basic technical skills he could just measure with a multimeter in AC mode the output of it. I know I ask a lot but I am kinda desperate

Should be a common part for NC-200, NC-410, NC-112, and NC-115 models too. Any other idea or advice I would be grateful!

Thanks a lot,

Duc.

LanceSulton · #2 10-05-2010, 10:12 AM

Just reach out to Eden (http://www.eden-electronics.com) ... I had the same problem with this amp years ago. Bad design, but they'll cop to the flaw and fix it (or provide the parts).

Duc · #3 10-06-2010, 03:57 PM

Thanks for your reply, I ve already sent them email asking for schematics, they did reply by just sending it but it doesn't states anywhere AC output voltage and thats all I wanted and explained to them. Do you still have this amp?!

BassmanPaul · #4 10-06-2010, 04:28 PM

It's kind of unusual for a transformer to be blown. They are very resilient. It's much more likely that the output stage is blown than the power transformer.

okcrum · #5 10-06-2010, 05:08 PM

Does the schematic tell you the DC voltages on the power amp rails, preamp rails, etc.? If so, you can figure out the transformer ratings from that based on the amp's output power.

Or just order a replacement transformer from Eden.

Duc · #6 10-06-2010, 05:30 PM

Well only the +15V & -15Volts that supply the preamp stage are mentioned. These are regulated from two zener diodes. I can send you the .pdf if you want to have a look in case I am blind or something

and if u can figure out something more would be great. And yes it is for sure a faulty transformer with primary windings shorted either because of its Chinese origin or from bad mains network with many surges or the combination of both...

okcrum · #7 10-06-2010, 06:28 PM

I have schematics for a number of the older Eden heads, but not the Nemesis stuff. They are not noted with the voltages either, but you can judge roughly by the ratings on the electrolytic filter and bypass caps. If they are, say, 80v, then you can bet that the rail voltage for the power amp is going to be somewhere in the +-60-70 v range.

The output transistor ratings won't help as much, as they are generally rated for at least 100V.

BassmanPaul · #8 10-07-2010, 10:28 AM

Quote:

Originally Posted by Duc

Well only the +15V & -15Volts that supply the preamp stage are mentioned. These are regulated from two zener diodes. I can send you the .pdf if you want to have a look in case I am blind or something

and if u can figure out something more would be great. And yes it is for sure a faulty transformer with primary windings shorted either because of its Chinese origin or from bad mains network with many surges or the combination of both...

Would you mind telling me how you came to this conclusion???

Duc · #9 10-07-2010, 02:27 PM

Well as LanceSulton mentioned above he had the same issue too and I also "heard" it from others through a research I did at various forums. I can't think any other logical reasons for such a robust passive component to fail, if you can think off any others you are welcome. Just a few minutes ago I got an answer from guys at Eden, it's 2 x 40Volts AC at secondaries. At last! Thanks a lot to all for your interest and replies.

okcrum · #10 10-07-2010, 02:44 PM

Quote:

Originally Posted by Duc

Well as LanceSulton mentioned above he had the same issue too and I also "heard" it from others through a research I did at various forums. I can't think any other logical reasons for such a robust passive component to fail, if you can think off any others you are welcome. Just a few minutes ago I got an answer from guys at Eden, it's 2 x 40Volts AC at secondaries. At last! Thanks a lot to all for your interest and replies.

That puts the power amp rails at about +- 56 volts at full load, and in the 60s while idling. We all trust you've ruled out other components as the cause of failure. Good Luck!

BassmanPaul · #11 10-07-2010, 02:48 PM

Sorry Duc if I pecking away at this. Just because the PT has failed before doesn't mean that it has in your case. The only way to ensure that the PT is faulty is disconnect ALL of the secondary windings and then test. This I failed to do when I was a lot younger. Replaced the transformer and was left with precisely the same fault. Turned out to be a short in the heater supply (tube amp).

Duc · #12 10-07-2010, 03:41 PM

I do amateur and semi pro servicing for more than 15 years, so some basic steps don't have to be mentioned I think

. Of course I desoldered every cable from the power supply board and test it again. To be honest I have no experience at all till now with tubes and luckily this one uses transistors so things are much simpler for me. If there was a fail at the power stage, regulation components would be the first to be affected and in worst case secondary windings would be cut off which is rare too. Now the primaries are shorted and thats why it blows mains fuse either with or without load. Note that it has two primaries for 110V and 220Volts markets which makes it a bit more sensitive maybe. Here we have 220 and some areas have very bad unstable mains with peaks. Tomorrow I ll order a handmade simple 300W 2x40V with one primary 220V winding only and I ll replace the 12V fan with a 220V to avoid the small circuitry that uses now both windings somehow. Btw recently I repaired a Peavey Tour 450 which was a pain in the ass to fix but now I can provide plenty of feedback and help to anyone interested including diagrams.

BassmanPaul · #13 10-07-2010, 04:10 PM

Fair enough Duc, I just didn't want you to make the same mistake that I did. It's a really horrible feeling to do a lot of work to find the original problem still exists. let us know how the repair turns out.

Duc · #14 10-22-2010, 03:05 AM

After some days of delay due to transformer maker the result rocks! Same dimensions, more wattage (300W) and more robust than original with only one primary. It hardly gets warm after long hard use at high volumes. I had to install an extra small 12Vdc pack just for the fan to bypass its original circuit. Thanks again for your interest.