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Old 30th December 2012, 09:48 AM   #11
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Ahh so its one of those jobs.

anyway I've moved onto a Nikko ND-390 II now...
Improving the sound quality coming from a Nikko ND-390 II, anyone got a schematic?
Click the image to open in full size.
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Last edited by freax; 30th December 2012 at 10:01 AM.
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Old 31st December 2012, 11:46 AM   #12
JMFahey is offline JMFahey  Argentina
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Unfortunately I see it being done today, all the time, as in Fender guitar amps (and many others)
Yes, they *do* use a primary fuse, but they mount *everything* on a big fweekin' PCB: Preamp, Power Amp, PSU (so far, so good) but also the mains fuse, and sometimes different mains taps (say, 120/240 windings and such) IN THE SAME big fweekin' PCB.
Of course, using 0.01 cent exposed fuse clips, and much worse, tracks and pads on same PCB.
So you unmount it to take a couple measurements (it's still "floating" over the metallic chassis, because it's hooked to the transformer), and you have to be 24/7 aware of that dangerous area, try to avoid it touching the chassis , etc.
At least the example shown above "stays where it is", you can work quite a few inches away on other PCB or whatever and/or cover it with tape or glue, but the Fender dangerous spot moves around during servicing, and the big PCB, being still tied to some wiring, has a mind of its own about where it wants to stay or move to.
I always slide a couple thick magazines between the chassis and the danger PCB zone, but it's a clunky solution at best.
Sometimes I disconnect the PCB mounted live fuse and momentarily add an external one, properly taped around like a mummy, while servicing lasts.
Oh well.
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Old 31st December 2012, 11:51 AM   #13
AJT is offline AJT  Philippines
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that is because only qualified technical persons are supposed to access these boards...
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Old 31st December 2012, 12:03 PM   #14
JMFahey is offline JMFahey  Argentina
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Yes, but even so, the design is poor (just to put it mildly).
Plus there is a *BIG* contradiction ... or call it double standards ... literally.
UL/CSA/TÜV/SEMKO/IEC/etc. rules have a very elaborate set of rules as to how dangerous voltages must be treated inside Electronic stuff, going to the extreme of stating "NO live voltage must be "touchable" inside, period" (I'm paraphrasing).
To the extreme of stating insulating caps or thermo contracting tubes must be used over all live terminals, creep distance between contacts, insulating "walls" between power switch terminals and so on.
So much so that Fender amps use different power switches for USA or Europe markets (they even show them on schematics), not because of line voltage but because of line safety regulations ... yet they leave exposed fuses, connection pads and as I said, pads and tracks of the SAME PCB .
I really don't know how they get approved and allowed to stamp the Safety conformity seals in the back panels.
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Old 31st December 2012, 08:25 PM   #15
Enzo is offline Enzo  United States
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I wonder. We are worried about the mains connections being exposed to the technician. I won't get into the other aspects. Yet open a tube amp and all the 500v conncetions and other B+ connections are exposed. If we are worried that a service technician will hurt himself touching the mains with his tools, we should be thinking about sealing the chassis so he can't open it, if he is that lacking in skills.

The power switch in those Fender amps is accessible to the outside world. All the stuff on the pc board is not. As to "all on the same board", look at any SMPS. For safety approvals, they need to have a certain amount of space between primary and secondary circuits. Being on the same board is not the issue.
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Old 31st December 2012, 09:36 PM   #16
Xoc1 is offline Xoc1  United Kingdom
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A lot of electronics have switch mode PSU units with rectified mains across the reservoir capacitors. Think of all of the pics of the DCX2496 you have seen on this site. How many have insulated the reservoir capacitor top in the PSU? In the UK that cap has over 330VDC exposed and that baby BITES! (as my brother found out when he touched it - he nearly threw up!)
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Old 9th January 2013, 06:43 PM   #17
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I find the Fender designs annoying as well. I wish only the secondary part of the transformer would have contact with the PCB. Keep the primary OFF the board!!!
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Old 10th January 2013, 02:44 AM   #18
JMFahey is offline JMFahey  Argentina
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Quote:
Keep the primary OFF the board!!!
+1
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