HK Audio Actor / Lucas power amps , generic problem?
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From: Gareth Magennis on 7 Jan 2010 11:51 "N_Cook" <diverse(a)tcp.co.uk> wrote in message news:hi4kpm$5dr$1(a)news.eternal-september.org... > Gareth Magennis <sound.service(a)btconnect.com> wrote in message > news:0di1n.3070$2F5.2360(a)newsfe07.ams2... >> >> >> "Gareth Magennis" <sound.service(a)btconnect.com> wrote in message >> news:E7i1n.3069$2F5.2098(a)newsfe07.ams2... >> > >> > >> > "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message >> > news:oWb1n.11179$mQ.2517(a)newsfe01.ams2... >> >> >> >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message >> >> news:hi1o7d$fic$1(a)news.eternal-september.org... >> >>> >> >>> 20 degrees is about the most or you block off access to the TO3s. > Maybe >> >>> only >> >>> tinkering at the heat build up problem. Most air must go through the >> >> Oh, BTW, can you confirm which way the fans run? Sucking air out the >> cabinet or blowing it in? >> >> >> >> Gareth. >> > > This one is outwards > 4,000 sq mm of purpose built inlet holes and 3,300 sq mm through fan vent > I > would have thought was quite adequate if the air was directed over the > heatsinks and not wind-breaked. This one permanent mounted high up away > from > floor dust. > Compared with Laney CD850 , totally inadequate constriction on outlet over > fan . > 3 of those I've cut away the "vent" holes over the fan, fared off and > covered with a wire grille and they've not bounced back (each was cutting > out thermally after extended but normal use) > As the Laney original design just 14 small slots with a combined area of > only 1.5 sq > inches, let alone vortexing, so overloading the 3 inch diameter fan > with through ducted area of about 6 sq ins , ridiculous aerodynamics > > Thought so. I did once think about reversing the fan, blowing air into the amplifier, but there is too much risk of the impeller being fouled by a blow to the casing around the vents. Surely this would mean more internal turbulence, thus better cooling? It must have been designed this way round for a reason, though, (?) so I gave up on that idea. Gareth.
From: N_Cook on 7 Jan 2010 12:13 Gareth Magennis <sound.service(a)btconnect.com> wrote in message news:CLydncjRzLu0jNvWnZ2dnUVZ7oOdnZ2d(a)bt.com... > > "N_Cook" <diverse(a)tcp.co.uk> wrote in message > news:hi4kpm$5dr$1(a)news.eternal-september.org... > > Gareth Magennis <sound.service(a)btconnect.com> wrote in message > > news:0di1n.3070$2F5.2360(a)newsfe07.ams2... > >> > >> > >> "Gareth Magennis" <sound.service(a)btconnect.com> wrote in message > >> news:E7i1n.3069$2F5.2098(a)newsfe07.ams2... > >> > > >> > > >> > "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message > >> > news:oWb1n.11179$mQ.2517(a)newsfe01.ams2... > >> >> > >> >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message > >> >> news:hi1o7d$fic$1(a)news.eternal-september.org... > >> >>> > > > > Thought so. > I did once think about reversing the fan, blowing air into the amplifier, > but there is too much risk of the impeller being fouled by a blow to the > casing around the vents. Surely this would mean more internal turbulence, > thus better cooling? > It must have been designed this way round for a reason, though, (?) so I > gave up on that idea. > > > > Gareth. > > The main disadvantage that way round is all internal stuff gets heated up to some intermediary temperature, between ambient and heatsink temp
From: Gareth Magennis on 7 Jan 2010 14:14 "N_Cook" <diverse(a)tcp.co.uk> wrote in message news:hi4t13$q18$1(a)news.eternal-september.org... > Gareth Magennis <sound.service(a)btconnect.com> wrote in message > news:Af61n.20179$AV4.16792(a)newsfe04.ams2... >> >> >> "Ron" <ron(a)lunevalleyaudio.com> wrote in message >> news:FMWdnar5p5rYhd7WnZ2dnUVZ8nGdnZ2d(a)bt.com... >> > On 05/01/2010 09:59, Arfa Daily wrote: >> >> "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. >> > >> > 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) >> >> >> Well, I agree with Arfa and Ron. I've repaired lots too, since the > cooling >> is also IMHO inadequate, which is quickly made worse by fluff around the > fan >> vents. >> Never had any dry joints, but seen plenty of the bulging caps Ron > mentioned. >> I replace them with 105 degree types regardless of apparent condition. >> >> One warning - it is easy to accidentally short the solder tags the big >> diodes are soldered to, to the zero ohm links as you tighten the nuts. >> If >> you power up fully in this condition with 4 amp fuses you will blow the >> Darlingtons again. >> You have probably noticed both speaker output tags have amplifiers on > them, >> there is no grounded speaker connection, though each output is referenced > to >> ground. >> >> >> >> Gareth. >> > > I see no circuitwise reason for those repeated cap failures. The > Darlington > heatsinks are elevated off the pcb (trackside) with spacers and although > the minor component side of the pa pcb is un-fanned I would not have > thought > pcb and working caps would get to 85 deg C > Will make airflow mods and RTV-stick non-resettable thermochromic dots > around various items , for if it bounces back. > > Maybe a batch of dodgy caps, along with the dodgy Darlingtons?! 100v 105C caps are not exactly expensive or physically large, so a bit of a no brainer for bullet proofing this application. Gareth.
From: N_Cook on 8 Jan 2010 03:42 > > > Maybe a batch of dodgy caps, along with the dodgy Darlingtons?! > > 100v 105C caps are not exactly expensive or physically large, so a bit of a > no brainer for bullet proofing this application. > > > > > Gareth. > no room for that size, unless put on track side of the pcb . As it happens space there and as the temp sensing TO220 s and fan air flow/temp sensor that side already I will solder replacements on that side I think
From: Arfa Daily on 8 Jan 2010 21:04
>> >> That was my definition of inadequate. The fact that 3 of us here have >> seen large quantities of the same units with the exact same problems bear >> this out. >> I'm sure we've all seen plenty of amplifiers with a whole ton of dust >> inside that have been working hard for years. >> >> I had a theory that because once repaired they tend not to come back, >> this may point to either a manufacturing issue or dodgy batch of >> Darlingtons (?) >> >> >> >> Gareth. >> >> > > > Oh, BTW, can you confirm which way the fans run? Sucking air out the > cabinet or blowing it in? > > > > Gareth. I'd never really considered a dodgy batch of transistors. I'd always put it down to the cooling becoming poor when the fan grille got clogged, leading to the paste frying to dust, and the transistors then overheating with little or no compensation from the flatpak transistor in contact with the underside of the heatsink. I have always obtained my transistors for these from Farnell, but I noticed last time I ordered a few weeks back, that the price of them seems to have gone up quite a bit from what I remember them being last time ... You know, off the top of my head, I really can't remember if the fan sucks or blows. I should have been able to tell you today, as the shop that I do a lot of these for, primed me earlier in the week for one that was coming in as an urgent repair, as the band had a gig Saturday night. It hasn't arrived, so if it does turn up tomorrow (ha! - today now!), the repair cost has doubled ... :-) I seem to think that the fan sucks air into the cab, which is what causes the clog at the grille, but could be wrong. Oh to be young again, with a head that stores things with total recall :-\ Arfa |