Ron wrote in message
...
On 05/01/2010 09:59, Arfa Daily wrote:
wrote in message
...
They have an otherwise original assembly method of the final contact to
the
pins of TO3 power transistors by 2 zero ohm "resistor" links, so 2
current
paths to the pcb traces. Anyone else observed bad solder joints to
these
links on the pcb? and cause? believed conventional solder not PbF





I repair many of these, and can honestly say that I have *never*
observed
any bad joints at the place you mention. By far the commonest problem is
failed output transistors. This occurs because the heatsinks are only
just
about adequate with proper cooling. As soon as the fan air intake vents
start to clog up with fluff, the outputs start to run too hot. Over a
period
of time, this dries out the heatsink paste to a powder, leading
ultimately
to transistor failure.

Whenever I get one, I always remove the other pair of transistors as
well,
clean down their heatsinks, and re-paste them, not forgetting the
flatpak
transistor that's in contact with the underside of one heatsink on each
channel.

The manufacturers recommend that when the outputs are replaced, two of
the
BC546Bs nearby are replaced as well (T7 / 8 on one channel, 10 / 11 on
the
other). Check also C3 and C21 to make sure that they are not bulging.

Other than this, these amps are very well behaved, and new outputs and
fuses
will, in 99.9% of cases, effect a complete cure. Note, however, that
they
have proper differential inputs, so are not that easy to drive
correctly,
unless you have a proper balanced XLR source, and that they don't like
earthed test equipment connected to their outputs / inputs
simultaneously. I
usually hook a completely isolated speaker to them for final check, as
the
music shop which sends these to me for repair, often remove the amp
chassis
from the cab, to ease the transport, and save me having to strip it all
out.
He now tells customers when they collect the repaired unit, that they
should
brush out the air vents at three monthly intervals.

I agree with Arfa, I`ve repaired dozens of these and always found the
solderwork to be excellent. Perhaps someone else has been in there
before you. There was a mod for early units, different output
transistors and the addition of a couple of 1N7007 on the print side of
the board.

Ron(UK)


Amp seems 2004 but replacement devices of matching dates on each pair of
2006 and 2007, looks wll enough done repair, he would have seen any
associated duff solder points in the process, surely. I don't like the
closeness of the +/- live vanes of the h/s on a board that can easily flex
with heat.