HK Audio Actor / Lucas power amps , generic problem?

05/01/2010 - 10:15 von N_Cook | Report spam
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
 

Lesen sie die antworten

#1 Arfa Daily
05/01/2010 - 10:59 | Warnen spam
"N_Cook" wrote in message
news:hhv006$kqa$
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.

Arfa

Ähnliche fragen