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Old 7th December 2005, 09:22 AM   #1
Nordic is offline Nordic  South Africa
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Unhappy Just got to vent a bit.

Just got to vent a bit.

After struggeling for hours to take the amp apart I built last weekend, redesigning the PSU, snubbering the bridge rectifiers, I went and connected the power cable between the PSU and amp the wrong way around...

For those of you who wondered what happens... well lets just say alot of smoke and stink gets released into the air from the chips, and they both have melted bits.

Man I just feel like crying, those were my last 2 LM3875 chips, and I probably ****** up the 4 brand new 10000ufd caps I bought with my last pocketmoney, and probably the 4 1000ufd ones too.

I thought this would make me feel better, actualy now I want to get my old goth boots with the metal sole inlays and go and jump on every component I see in the house!!!!!!!!!
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Old 7th December 2005, 09:38 AM   #2
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Bummer! Well, I know the feeling. Blew up too many chips myself. Before I started to put reverse diodes across the amp supply rails all the time. ..

Your caps may still be OK though, this may be one of those events where the chips blow to protect the caps. Supply still OK?

Jan Didden
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Old 7th December 2005, 09:49 AM   #3
Nordic is offline Nordic  South Africa
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Cut off the wires to the amp, as it is definatley toast, reversed polarity from psu and fired it up, had nothing to loose as I did hear the bubbling sound thing from the caps at the time... I do get DC, but how can I tell if the caps are screwed without a meter?

Oh well will have to find something else now to occupy me for the next 2 weeks, as I don't have the resources to replace anything before then, and even then it is going to be a hunt AND wait to get new chips here... ******* just love living in the third world on days like this. NOT!

Dunno if its the timing or what, have broken many things in my time, but this time I took it personaly, almost like I now want nothing to do with the amp. Weird ****ed off emotion.

Edit, looks like the site thinks I said many bad words.... guess its not impossible....

Could you show me an example of the diode thing you do...
Voor ek het amp stukkend skop.
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Old 7th December 2005, 11:18 AM   #4
Nordic is offline Nordic  South Africa
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Got to vent some more!!!!!!!!!!!!!! the earliest I can land 2 replacement chips is in something like 14 days...
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Old 7th December 2005, 11:34 AM   #5
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You put in a diode from V= to ground and V- to ground, in reverse direction. So, when all if fine, they don't conduct, its as if they are not there. If for some reason you reverse connect the supply, they conduct and hopefully blow your fuses. You DID have fuses, right?

Anyway, if the supply stays up and you have the right voltage on the caps they are probably OK. Since the chips shorted the supply your caps most likely never saw the reversed voltage anyway. And if the caps were broken they would fail as a short and you wouldn't be able to bring up the supply again. Consider yourself lucky, feels much better than the opposite

Jan Didden
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Old 7th December 2005, 11:49 AM   #6
Nordic is offline Nordic  South Africa
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Thanks Jan, although this was not a terribly expensive lesson (well, it is when you are a bit broke like me), it is a rail pain, due to the inconvenience of sourceing replacement chips.

National's local distributors don't stock loose chips, and can only help quickly if I take a 20 chip tube, else they order the loose ones from National, ergo the long wait.
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Old 8th December 2005, 02:24 PM   #7
Wynand is offline Wynand  South Africa
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I must agree with Nordic on this one. I think that electronics suppliers in South Africa (Cape Town for us 2 ) needs a kick on the B-hind.

Origeonally I could only find LM3876 at mantech.... Now I found LM3886.... for R20 cheaper but the rest is impossible...

Luckily I work for small electronics company and was able to get 4 x LM4780 as samples... but I wont be able to get more.

Wish I could help Nordic.
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Old 8th December 2005, 04:21 PM   #8
Nordic is offline Nordic  South Africa
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Think I'm just going to get them as samples from National, I would gladly have bought them, in fact it would be cheaper than the $16 I have to pay national for it.
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Old 9th December 2005, 01:16 AM   #9
karma is offline karma  Canada
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dont feel bad i lost one of my lm4780 this week to static first for me. i take so much care into building and handling of the parts
just for this to happen.


i feel your pain
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Old 9th December 2005, 10:41 AM   #10
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Yes i can understand your frustration.. I also connected the supply in reverse, but was very lucky in that the diodes only started to smoke before i mahaged to turn the power off, And that was after checking and rechecking, i just about gave up.
But I'm sooooooo glad i didn't

Just a quick question.............I have recently got some samples from Nat. Has anyone actually put a second order in and gotten a second batch free?
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