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Thread: Does anyone do surface-mounted component repair?

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    Supporting Member Axtman's Avatar
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    Does anyone do surface-mounted component repair?

    I have a Carvin AG300 acoustic amplifier that I would like to send to someone on this forum and I would pay for the repair. I do not have the equipment to do surface-mounted component repair plus the circuit is quite a complex Class D amplifier with digital effects.

    Is anyone interested in repairing this amp for me? Thanks.

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    Last edited by Axtman; 01-10-2020 at 12:40 AM.

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    Supporting Member The Dude's Avatar
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    I know you don't want to fix it, but posting the schematic if someone wants to have a look. According to Carvin, the AG200 and AG300 share a schematic. What's wrong with it?

    https://cdn.shopify.com/s/files/1/04...76308065722121

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    I'm busy enough as it is, but I've been doing SMD work for twenty years.
    With the right soldering station and a magnifying light fixture it's the same as any other work.

    Repaired one of a pair of pretty expensive studio monitors today after the 100w class D chips came in.
    I'll do the other tomorrow, hopefully it will go as easy.

    Seriously, you just need a large magnifier and it's not bad to fix this stuff.

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    Lifetime Member Enzo's Avatar
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    I did SM stuff for a long time, it is just a new technique to know. Kinda like playing guitar for years, then learning to do slide/bottleneck play. or learning fretless bass after years of regular fretted. Circuits are circuits otherwise.

    there are a bunch of very skilled quality techs here, but really, in a city the size of Seattle, there are no competent amp techs?

    A friend of mine is learning the arcane art of amp repair, and I am helping him in this. he is scared silly of "solid state" amps. "I don't know anything about them" he wails. A Lab Series amp came in recently and he was all tense about it. Turned out the problem was blown speakers, the amp was fine. Why am I telling this? Dude asked the magic question:what is wrong with it? So far we don't know that the complicated class D circuit is even involved.

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    Supporting Member Axtman's Avatar
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    The problem is that the amp does not even turn on, so far as I can tell.

    As you know most modern stuff is really not designed to be repaired.

    I am checking around town but most repair places are not really interested in looking at it.

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    Lifetime Member Enzo's Avatar
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    Did you know, as a tech, "Dead" is usually among the easiest repairs. Lots simpler than "sometimes distorts".

    As you know most modern stuff is really not designed to be repaired.
    This is simply not true. I worked on the stuff all the time. I was an authorized repair shop for most major brands, and we repaired SM stuff every day. it just requires tools and skills. Imagine playing cello all your life, then picking up a mandolin. Would you assume it was not meant to be played?

    Harman lists these guys:

    Sound West Audio
    2323 Tacoma Avenue South
    Tacoma, WA 98402
    (253) 272-1435

    service@soundwestaudio.com

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    Dead amps are my favourite repair. An amp that sometimes loses treble for a few minutes after two hours of hard playing that does it once every few weeks is the worst kind. I don't have specialized SMD repair gear either. I have my regular tools - a solder station with a fine tip, various tweezers and dental picks and my bench magnifier. The only specialist SMD consumables are some rework gel flux and a few packs of Chipquik. I repair SMD stuff regularly. The schematics are the same, components check the same, diagnosis is the same as through hole. I prefer through hole, but without doing SMD I'd be turning away a lot of work and be stuck in the past.

    I don't think most consumer equipment is specifically designed to be repaired. It never really was - it was designed to be manufactured in the cheapest and most efficient way and I doubt much thought was given to repair. Unlike industrial, medical or military equipment where it may be mandatory. Maybe Traynor did think it through with the amps where the chassis didn't even need to be removed from the cabinet to access the electronics. It's just that manufacturing techniques have changed and we have to keep up with the changes. When boards were stuffed by hand then the repair process was a reverse of those that went into making them. The same applies with SMD, it's just the scale is reduced and we have to think how the component can be removed/replaced as a reflection of manufacturing techniques.

    The greatest challenge is the cost of Western labour rates compared to Far-Eastern factory gate prices for boards. How much time could you put in to make a repair on a $4.50 board cost-effective? A boad where no human actually touched anything during its manufacture. That's exactly the price I pay for a 100W class D entire power amp PCB fully populated.

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    Supporting Member Axtman's Avatar
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    Okay okay! I will check it out myself.

    I think the problem is with the switch mode power supply....of which I know nothing of their operation. I guess now is time to learn.

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    Lifetime Member Enzo's Avatar
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    My opening advice on SMPS:

    Know that they rectify and filter the mains DIRECTLY and so you will typically find 340vDC in the primary side circuits, with plenty of current to kill you if you are not cautious.

    SMPS typically have a lot of self protection. SO something like the power amp they serve can cause them to shut down. In other words a blown amp can make the SMPS refuse to operate. And the SMPS itself will shut down if for example one of its rectifiers is shorted.

    So sometimes the SMPS is "dead" but not defective.

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