[Serow]

I built my first cmoy last night, using a DC jack and Wall wart power supply. When I tested it, it worked fine. However, I noticed today that I had the positive and negative poles of the power jack shorted together. Would this damage the amp or BUF634 virtual ground buffer? As far as I can tell, since the amp and the short were in parallel, the only thing that would have happened would be that a lot of current would have flowed through the short, but the rest of the amp would have not even noticed a difference.

Thanks for your help,
Eric

 

[thomas]

yep, you're right, there would be lots of current flowing through the shorted area, but the circuit should be fine...

Well, your power supply might be damaged/blown a fuse, but the amp should be fine...

 

[Serow]

Thanks for the reply. It seems to work fine now that I have fixed the short, but I'm somewhat worried that there may be damage to the amp that I can't detect.

 

[Apheared]

Solve that before applying power again! You can send that unprotected wallwart to a smoky grave very quickly...

You're probably ok... BUT... Think a power supply short can't fry stuff downstream? heh go ahead, think that!

 

[Serow]

Apheared, how would I be able to check if the short (which I have fixed) fried some of the components? BTW, I was just trying to remain in denial.

 

[Apheared]

Resistors are easy; between looking at them and measuring them... that's it.

Capacitors... you can test em for being shorted or if they're leaky with a multimeter... but beyond that, not much. The easiest way is to swap it with a known good one.

Testing opamps?! Oh crap. Not really possible. So try this method: WORKS=GOOD, BROKE=BAD... How's that for technical troubleshooting?

You gotta consider, you've got a stack of transistors and matching passives all in-circuit here... on a microscopic chip... and no way to separate the parts. If it works, consider it perfect or swap it if you think it's damaged... there's nothing you can do.

We had a different sort of thread a few months back on HW about how to store them; that some chips sound different after being stored a certain way - they might have been damaged ever so slightly but still function.

 

[rickcr42]

not to mention "slightly" damaged or "marginal" chips.Not always an all or nothing deal,you can damge the input FETs on a chip and still pass a signal,not the best signal but a signal

this REALLY plays hell with troubleshooting a circuit,a straight go/no go is easy,as is a totally fubar part,but intermittant or marginal will drive a rational person to the edge (not that I am rational)

Also be aware that resistors can and co change value if too long under the soldering iron , or if the device in question overheats-same ****

caps are usually bullet proof unless hit with a reverse polarity,dead short,or overvoltage (you will know ,they whistle right before they OOZE,really,no ****)

AND-just for GP info

You can not measure a resistor "in circuit",you will not get a correct reading.You must de-solder one end and then measure it

Ain't this **** FUN

 

[thomas]

btw, do you guys have all that ESD protection stuff like wrist straps, antistatic matts, grounded tip irons, hand lotions, air ionizers, etc...

In the actual industry, they use all that and much more, but i never took esd protection too seriously until i saw that tread/saw how "real" technicians/technologists do it...

judging by that discussion back at headwize, it would seem that you would compromise the performance everytime you handle an opamp or semiconductor?

I usually use IC sockets, test the voltage once (so i don't fry opamps), then pull out the ICs with tweezers by the plastic case, and put them in... (i also have an el-cheapo air cleaner with ionizer, don't think it does anything other than suck up the poisonous fumes) Is what i'm doing enough, or could there still possibly be ESD damage?

 

[rickcr42]

I have a big ass deap sea fishing sinker on my bench that has a 12 guage wire that goes to the groung connection of the AC outlet.I touch this as step one

step two is the wrist starp,I am a walking shock man,really,I touch my jeep i get a shock

Next-I NEVER test a device as a complete unit first

Back in the stoneage I would do it that way and man did it cost me,parts were not cheap then (how 'bout $6-8 per transistor in a push pull amp !)

Always check the psu,fist with no load,then with.If the polarity checks out and the voltage is within specs,discharge the filter caps,connect the actual circuit,plug'er in AND DUCK !

just kiddin'

Gotta get the psu correct first,all else follows

Rickamundo

 

[Serow]

Well, I'm going to call it perfect and hope that my headphones don't burst into flames a hundred hours down the road

. The rails measure +12.75 and -12.79, and I measured a current draw of 20 mA with 2 2134 opamps and one buf634 in low bandwidth mode. The DC offsets are both less than 2 mA.

Sounds (and measures) damn good to me.

P.S. Anyone that thinks the Sony V6 don't need an amp have never tried them using one...

Thanks for the help,
Eric

 

[Apheared]

plug'er in AND DUCK !

See, I thought that went away once you knew what you were doin... but nope!

You expect it to do what you want, you know it's going to... you planned, you tested...

But it still comes down to flippin' the switch and seein' what happens. hehe and as Rick(ie don't lose that number) points out, when it's expensive crap down there, you do have this... feeling... of relief when the magic smoke doesn't escape.

 

[Serow]

I think this issue can be safely called resolved. Surprisingly, I didn't even see any magic smoke escape from the poor wall wart. I think I'll use that wall wart for less important projects - like one of my father's.

I will post pictures and descriptions as soon as I can go through a whole roll of film and get it developed. No crappy digital cameras for me!