HK Audio Actor / Lucas power amps , generic problem?
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From: N_Cook on 5 Jan 2010 06:53 Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message news:64E0n.252$It5.117(a)newsfe03.ams2... > > "N_Cook" <diverse(a)tcp.co.uk> wrote in message > news:hhv006$kqa$1(a)news.eternal-september.org... > > 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 > > Thanks for that - both of those caps are bulging, I had not noticed up to now. I will replace those and the TO92s. A tip in reply for these and other apparatus with that grey interconnect ribbon. Before removing any such boards I run some hot-melt glue down the join of the cables at and to the board. So any bending, you have to do, is then only in the cable run which consists of multistrand but soldered wire, so will easily break where not supported by the grey plastic sheathing, ie at the ends, where it otherwise would choose to bend. I would have thought the ducted air design was about ideal for a given fan size, but I will bend inwards the outer fingers between the +/- dc carrying adjascent heatsinks. Perhaps the airstream takes the path of least resistance and does not pass through the 44 vane version of this type http://www.elfa.lv/images/tn/d9b8dde0-803b-11dd-9ab0-005056b94d7a.jpg staggered fingers of those square format heatsinks and goes around outside instead. Perhaps bending inwards all 20 internal run fingers of each h/s would be a sensible mod, less vortexing/blocking, more open, would make less of a dust trap as well
From: N_Cook on 5 Jan 2010 08:48 The sort of wide pitched grey ribbon that has end stripped and conductors soldered directly to pcb, rather than headers
From: Arfa Daily on 5 Jan 2010 12:56 "N_Cook" <diverse(a)tcp.co.uk> wrote in message news:hhv996$5vk$1(a)news.eternal-september.org... > Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message > news:64E0n.252$It5.117(a)newsfe03.ams2... >> >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message >> news:hhv006$kqa$1(a)news.eternal-september.org... >> > 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 >> >> > > Thanks for that - both of those caps are bulging, I had not noticed up to > now. I will replace those and the TO92s. A tip in reply for these and > other > apparatus with that grey interconnect ribbon. Before removing any such > boards I run some hot-melt glue down the join of the cables at and to the > board. So any bending, you have to do, is then only in the cable run which > consists of multistrand but soldered wire, so will easily break where not > supported by the grey plastic sheathing, ie at the ends, where it > otherwise > would choose to bend. > I would have thought the ducted air design was about ideal for a given fan > size, but I will bend inwards the outer fingers between the +/- dc > carrying > adjascent heatsinks. Perhaps the airstream takes the path of least > resistance and does not pass through the 44 vane version of this type > http://www.elfa.lv/images/tn/d9b8dde0-803b-11dd-9ab0-005056b94d7a.jpg > staggered fingers of those square format heatsinks and goes around outside > instead. Perhaps bending inwards all 20 internal run fingers of each h/s > would be a sensible mod, less vortexing/blocking, more open, would make > less > of a dust trap as well > > Having a great deal of experience of these, I feel they are a fundamentally well-designed and constructed amp - both electronically and mechanically, and I don't think that I would contemplate altering any aspect away from the way it was designed, including the arrangement of the heatsink fins, and the airflow paths. The heatsinking and cooling of the heatsinks *is* adequate as designed, but becomes a bit marginal if the units are thrashed hard on a regular basis, whilst the air intake vents are allowed to clog. If the transistors / heatsinks of both channels are cleaned down and repasted during the repair process, and the owner is alerted to the importance of just scrubbing a soft paintbrush around the vents once in a while, they are unlikely to give further trouble. I've never had any repeat failure issues with them, anyway. I take your point about the inner 'row' of fingers, but I don't think I would feel inclined to bend them in more than a few degrees, otherwise, they might actually block convection off the transistor cases ?? Arfa
From: N_Cook on 6 Jan 2010 03:10 Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message news:W2L0n.12625$AV4.245(a)newsfe04.ams2... > > "N_Cook" <diverse(a)tcp.co.uk> wrote in message > news:hhv996$5vk$1(a)news.eternal-september.org... > > Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message > > news:64E0n.252$It5.117(a)newsfe03.ams2... > >> > >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message > >> news:hhv006$kqa$1(a)news.eternal-september.org... > >> > 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 > >> > >> > > > > Thanks for that - both of those caps are bulging, I had not noticed up to > > now. I will replace those and the TO92s. A tip in reply for these and > > other > > apparatus with that grey interconnect ribbon. Before removing any such > > boards I run some hot-melt glue down the join of the cables at and to the > > board. So any bending, you have to do, is then only in the cable run which > > consists of multistrand but soldered wire, so will easily break where not > > supported by the grey plastic sheathing, ie at the ends, where it > > otherwise > > would choose to bend. > > I would have thought the ducted air design was about ideal for a given fan > > size, but I will bend inwards the outer fingers between the +/- dc > > carrying > > adjascent heatsinks. Perhaps the airstream takes the path of least > > resistance and does not pass through the 44 vane version of this type > > http://www.elfa.lv/images/tn/d9b8dde0-803b-11dd-9ab0-005056b94d7a.jpg > > staggered fingers of those square format heatsinks and goes around outside > > instead. Perhaps bending inwards all 20 internal run fingers of each h/s > > would be a sensible mod, less vortexing/blocking, more open, would make > > less > > of a dust trap as well > > > > > Having a great deal of experience of these, I feel they are a fundamentally > well-designed and constructed amp - both electronically and mechanically, > and I don't think that I would contemplate altering any aspect away from the > way it was designed, including the arrangement of the heatsink fins, and the > airflow paths. The heatsinking and cooling of the heatsinks *is* adequate as > designed, but becomes a bit marginal if the units are thrashed hard on a > regular basis, whilst the air intake vents are allowed to clog. If the > transistors / heatsinks of both channels are cleaned down and repasted > during the repair process, and the owner is alerted to the importance of > just scrubbing a soft paintbrush around the vents once in a while, they are > unlikely to give further trouble. I've never had any repeat failure issues > with them, anyway. > > I take your point about the inner 'row' of fingers, but I don't think I > would feel inclined to bend them in more than a few degrees, otherwise, they > might actually block convection off the transistor cases ?? > > Arfa > > The good pair had good solder points under. All white goo was in oily state, One of those electros was o/c the other high ESR and both had more obvious bulge at the lead end
From: N_Cook on 6 Jan 2010 03:29
Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message news:W2L0n.12625$AV4.245(a)newsfe04.ams2... > > "N_Cook" <diverse(a)tcp.co.uk> wrote in message > news:hhv996$5vk$1(a)news.eternal-september.org... > > Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message > > news:64E0n.252$It5.117(a)newsfe03.ams2... > >> > >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message > >> news:hhv006$kqa$1(a)news.eternal-september.org... > > > Having a great deal of experience of these, I feel they are a fundamentally > well-designed and constructed amp - both electronically and mechanically, > and I don't think that I would contemplate altering any aspect away from the > way it was designed, including the arrangement of the heatsink fins, and the > airflow paths. The heatsinking and cooling of the heatsinks *is* adequate as > designed, but becomes a bit marginal if the units are thrashed hard on a > regular basis, whilst the air intake vents are allowed to clog. If the > transistors / heatsinks of both channels are cleaned down and repasted > during the repair process, and the owner is alerted to the importance of > just scrubbing a soft paintbrush around the vents once in a while, they are > unlikely to give further trouble. I've never had any repeat failure issues > with them, anyway. > > I take your point about the inner 'row' of fingers, but I don't think I > would feel inclined to bend them in more than a few degrees, otherwise, they > might actually block convection off the transistor cases ?? > > Arfa > > I have to differ on the aerodynamics. This sort of 4mm wide double wall, staggered finger design, is for convection not passage of air through. Walls of 4mm gap blocked by 4mm finger repeated four times each side of the fan (2 h/s in line each side) is pretty effective wind break. Then 2 "gaps down the sides of 3mm wide x 35mm high and 70 mm long is similarly "resistive". Most cooling would be the 2 outer edges of 12 only of the 44 vanes each h/s where there is unobstructed passage outside the heatsinks and out to the surrounding duct |