Power Amp Repair

[Meat Plow]

On Wed, 07 Feb 2007 07:22:53 -0800, Haaky Has Frothed:

[SNIP]
I think you nailed it on the head. It did seem strange to see the
different output trans in there. I'm thinking that because if that
whoever owned the amp before
me must have had it in for repair. Or it might have even come from the
factory that way. Due to shortage of parts.

There are always tell-tale marks when components have been
de/resoldered.


My old apprentice mentor many many years back, told me that the only way
you
should be able to tell that a component has been replaced, is if the
soldering is *better* than the manufacturers original ! A good maxim I
think, and one that has stuck by me for my whole life in the business. I
never use too little solder on a joint, nor too much, and always clean
off
the flux residue.

Arfa

As do I but I've seen some real hack jobs in my days.

I sometimes wonder how some of the work that I see has lasted as long as it
has. I can't believe that anyone can have made such scruffy-looking, and
sometimes even mechanically and electrically poor joints, and been satisfied
to declare the job " a good 'un ", and send it on its way !! I
contract-repair large quantities of a power driver board that comes from a
particular drinks vending machine. I took this work from another repair
outfit, because the drinks machine suppliers, were not happy with the long
term reliability that they were getting on the repairs. I still see ones
that he repaired a couple of years ago, coming back now. Electrically, the
repairs were OK, but you have never seen such scruffy work in all your life.
It looks as though the joints were made with a poker heated in the fire,
plumber's solder, and paste flux ... Often, link print between two adjacent
components, is missing, and the link has had to be made by bending over the
leg on the replaced component. It's criminal that such poor quality work
occurs, but more worryingly, if people such as this are carrying out
electronic repair work, are there similarly "qualified" people carrying out
work on your car ... ?

Arfa

LOL you and I do think alike in this respect at least. Back in the hay-day
of Citizen Band Radio in the US (late 70's)I worked with gentleman who
taught me a lot about the trade. We worked on a bunch of CB radios back
then. Many were from professional truck drivers some driving 80+ kilos and
over for our services. Many of these radios received emergency repairs
from truck stop chop shops which of course didn't last a week. I can
remember removing the cases and shaking my head in disgust at how
butchered some of these radios were. On the other hand when I started with
a company in the mid 80's doing major manufacturer warranty, all I worked
on was returns to large department stores and specialty electronics stores.
My specialty and training was vcr and mobile audio working on virgin units.
I took much pride and still do in my soldering techniques along with other
things like wire dressings and the likes.

 

[Arfa Daily]

On Thu, 08 Feb 2007 01:54:22 +0000, Arfa Daily Has Frothed:


On Wed, 07 Feb 2007 07:22:53 -0800, Haaky Has Frothed:

[SNIP]
I think you nailed it on the head. It did seem strange to see the
different output trans in there. I'm thinking that because if that
whoever owned the amp before
me must have had it in for repair. Or it might have even come from
the
factory that way. Due to shortage of parts.

There are always tell-tale marks when components have been
de/resoldered.


My old apprentice mentor many many years back, told me that the only
way
you
should be able to tell that a component has been replaced, is if the
soldering is *better* than the manufacturers original ! A good maxim I
think, and one that has stuck by me for my whole life in the business.
I
never use too little solder on a joint, nor too much, and always clean
off
the flux residue.

Arfa

As do I but I've seen some real hack jobs in my days.

I sometimes wonder how some of the work that I see has lasted as long as
it
has. I can't believe that anyone can have made such scruffy-looking, and
sometimes even mechanically and electrically poor joints, and been
satisfied
to declare the job " a good 'un ", and send it on its way !! I
contract-repair large quantities of a power driver board that comes from
a
particular drinks vending machine. I took this work from another repair
outfit, because the drinks machine suppliers, were not happy with the
long
term reliability that they were getting on the repairs. I still see ones
that he repaired a couple of years ago, coming back now. Electrically,
the
repairs were OK, but you have never seen such scruffy work in all your
life.
It looks as though the joints were made with a poker heated in the fire,
plumber's solder, and paste flux ... Often, link print between two
adjacent
components, is missing, and the link has had to be made by bending over
the
leg on the replaced component. It's criminal that such poor quality work
occurs, but more worryingly, if people such as this are carrying out
electronic repair work, are there similarly "qualified" people carrying
out
work on your car ... ?

Arfa

LOL you and I do think alike in this respect at least. Back in the hay-day
of Citizen Band Radio in the US (late 70's)I worked with gentleman who
taught me a lot about the trade. We worked on a bunch of CB radios back
then. Many were from professional truck drivers some driving 80+ kilos and
over for our services. Many of these radios received emergency repairs
from truck stop chop shops which of course didn't last a week. I can
remember removing the cases and shaking my head in disgust at how
butchered some of these radios were. On the other hand when I started with
a company in the mid 80's doing major manufacturer warranty, all I worked
on was returns to large department stores and specialty electronics
stores.
My specialty and training was vcr and mobile audio working on virgin
units.
I took much pride and still do in my soldering techniques along with other
things like wire dressings and the likes.

There's just not many of us left, I fear. One by one, we're all getting old
enough to retire, and there's just not the youth coming into the repair
business to train up to follow on from us. I too worked on what was then
illegal CBs here in the UK in the 70's, and then on the legal variety after
the implementation of the " 27 / 81 " legislation that made it so. The
illegal U.S. models used to be smuggled into the country from the continent,
inside frozen meat carcasses. Happy days putting in extra bands, roger
beeps, five-tones, sel calls, "K" beeps, FM conversions, splits and half
watt conversions. Lots of people used to do those just by sticking a bloody
great resistor in series with the feed to the PA, but it used to cause no
end of modulation compression problems on AM, so I used to do them with a
transistor and pot, which worked a lot nicer, and allowed exactly half a
watt to be set. Do you remember those " disguise " antennas that people used
to fit to cars. It was like a normal telescopic car antenna of the era, but
about twice as fat. People used to think that they were really invisible
with one of those, and a little Jaws II in the glove box, but I used to take
great delight in calling them with " Eyeball the breaker with the disguise
antenna !! " I had a pair of DV27's whipping about on the back of my car.
Looked like a fairground dodgem car ... Happy days, sadly long gone.

Arfa

 

[bananas]

please Haaic i need the schematics for the GX-300 if u can email me
[email protected] i will thank you a lo

 

[Eeyore]

please Haaic i need the schematics for the GX-300 if u can email me
[email protected] i will thank you a lot

You have another broken one ?

Graham

 

[bananas]

Thanks i really apreciate your help, my problem i think was cause
because an excesive input signal, i connected the cpu output directl
with the input of the amp, so always was working with constant clipin
in 8ohms, the fuse blows and when i open the amp the input phase wa
carbonized, so i change it for a new one with the seller, now i use
mixer but i encounter some problems, the fuse still blows, i ha
constructed a gx-300 clone with the exact components and works fine
but i still have the fuse problem in the clone