Well, this was my fault, and naive belief in the manufacturer.... I got this oldie C306 amp in perfectly working, untouched condition.
Being twenty-some years old,(the amp
) I thought it is about time to replace the rather cheapo looking electrolytics in it, and I was right, some of them measured only half of their original value.
So in the store I go, get the new ones, old ones out, new ones in, checked everything for shorts, solder joints, etc.
Boy, you should have seen this, the whole repertoir happening at once:
smoke, flame, bang, my heart almost stopped of the disbelief, what the heck happened?
Didn't take long to figure it out. Almost all manufacturers mark the polarity of electrolytics in a standard way, -either a dot, a circle around the negative leg, or a +/- marking on the PCB. Which was the case with the NAD too, EXCEPT..... they mark the positive leg with a circle, unlike most japanese, or german, or whatewer manufaturer.
So I've installed some 16 caps in the opposite way. Fortunately -do to the fused resistors employed-, I got away with 16 dead electrolytics, 4 fused resistors and 2 fuses "only".
After that of course I reinstalled everything the correct way, and fortunately now it works perfectly.
The morale of this? Don't work from routine, and always double or triple check everything after you repaired or modified something.
In these cases I do not use my trusty bulb tester (only replacing OK working parts with new ones), and I am not sure whether it could have prevented this from happening anyway.
Being twenty-some years old,(the amp
) I thought it is about time to replace the rather cheapo looking electrolytics in it, and I was right, some of them measured only half of their original value.So in the store I go, get the new ones, old ones out, new ones in, checked everything for shorts, solder joints, etc.
Boy, you should have seen this, the whole repertoir happening at once:
smoke, flame, bang, my heart almost stopped of the disbelief, what the heck happened?
Didn't take long to figure it out. Almost all manufacturers mark the polarity of electrolytics in a standard way, -either a dot, a circle around the negative leg, or a +/- marking on the PCB. Which was the case with the NAD too, EXCEPT..... they mark the positive leg with a circle, unlike most japanese, or german, or whatewer manufaturer.
So I've installed some 16 caps in the opposite way. Fortunately -do to the fused resistors employed-, I got away with 16 dead electrolytics, 4 fused resistors and 2 fuses "only".
After that of course I reinstalled everything the correct way, and fortunately now it works perfectly.
The morale of this? Don't work from routine, and always double or triple check everything after you repaired or modified something.
In these cases I do not use my trusty bulb tester (only replacing OK working parts with new ones), and I am not sure whether it could have prevented this from happening anyway.
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Now that you have had your coronary stress test for the year and a bit of "should have" learning experience, I bet you're happy everything is back to normal again.
A couple things I always do before doing anything to a piece of gear is snap a few close-up shots of the boards with my phone and grab a piece of scrap paper and some different colored sharpies. Never hurts to put a few colored dots on connectors of the same style/pin number and jot down a couple notes so things go back without question.
It is not at all unusual for there to be printing errors on the boards too and sometimes parts get added or changed in production that do not match the schematics or PCB print info.
The photos are a great way to double check your work just to make certain everything is back to the way it was when it worked for 20 plus years before finding out about your or the manufacturers mistakes the hard way.
After all, we're only human and everybody makes mistakes.
It does feel good when your life is back to normal again though doesn't it.
A couple things I always do before doing anything to a piece of gear is snap a few close-up shots of the boards with my phone and grab a piece of scrap paper and some different colored sharpies. Never hurts to put a few colored dots on connectors of the same style/pin number and jot down a couple notes so things go back without question.
It is not at all unusual for there to be printing errors on the boards too and sometimes parts get added or changed in production that do not match the schematics or PCB print info.
The photos are a great way to double check your work just to make certain everything is back to the way it was when it worked for 20 plus years before finding out about your or the manufacturers mistakes the hard way.
After all, we're only human and everybody makes mistakes.
It does feel good when your life is back to normal again though doesn't it.
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I made a similar folly with my C350 Integrated amp.
I thought it might be a good time to check and adjust the offset and bias, so I place my alligator meter leads on the test points and one tilts over and shorts to some component. Bye bye driver and output transistor
Ordered and replaced with new ones (not sure if NAD matches components at this grade level). Can't even tell they were replaced.
Lesson learned: make sure your alligator test leads are fully shielded so that they can't slip on you and short to something. Better yet, I made a couple of push on leads that are shielded, so now the meter lead ends are far and away from the components.
I thought it might be a good time to check and adjust the offset and bias, so I place my alligator meter leads on the test points and one tilts over and shorts to some component. Bye bye driver and output transistor
Ordered and replaced with new ones (not sure if NAD matches components at this grade level). Can't even tell they were replaced.
Lesson learned: make sure your alligator test leads are fully shielded so that they can't slip on you and short to something. Better yet, I made a couple of push on leads that are shielded, so now the meter lead ends are far and away from the components.
Actually, you should always use the bulb or other safety measures. What if you had installed all the parts correctly but one was shorted? Even new parts can have a bad one in the batch. What if in soldering them all in, you had left a small solder bead across two traces? or a trimmed lead remained? Something can always go wrong, even in the best of situations, and with high skill levels. I have been soldering over 60 years, and I always still protect myself from mistakes as well as I can. We all make them.
And would all those backwards caps have been saved by a bulb limiter? maybe. But I expect it would have prevented the smoke and flames, even if the caps were damaged by the reverse voltage.
Using a variac is the only way to safely power up equipment in a manner that can save components and damage during power-up. A variac is a variable AC transformer that allows you to increase the mains voltage and hold it while you do checks at a few circuit positions.
The bulb limiter applies full AC line voltage until the filament heats up. That takes a few moments. After that point in time the bulb will only limit the energy into your equipment, hopefully limiting the actual damage. It is better than nothing, but it brings a bunch of characteristics to the table that you have to familiarize yourself with.
A small variac was among the first bits of equipment I bought when I was setting my experiments bench up as a young lad. I use a variac every time I power something up for the first time.
-Chris
The bulb limiter applies full AC line voltage until the filament heats up. That takes a few moments. After that point in time the bulb will only limit the energy into your equipment, hopefully limiting the actual damage. It is better than nothing, but it brings a bunch of characteristics to the table that you have to familiarize yourself with.
A small variac was among the first bits of equipment I bought when I was setting my experiments bench up as a young lad. I use a variac every time I power something up for the first time.
-Chris
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