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
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.
a
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
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
Yes, they are a little odd around the output stages in terms of what can be connected. They get very upset if you connect a dummy load with a ground common to your scope ground, and the ground of the signal generator ...
I'd never considered that hot-plugging the sats might be an issue, but I will mention that to the shop as something to tell punters not to do, as he has quite a few of these rigs that he uses for rental.
On a different subject, you know a bit about bingo don't you ? Know anything of the maths or concept behind the RNG that used for producing the numbers. I've found a number of patterns appearing, which seem to make the 'randomness' a lot less than you might have believed. Can't seem to find anything much relevant about this, on t'net.
Arfa
Could that be because each pair of amps might run in opposing polarities, the bass speaker is driven by two amps in bridge mode?
I do have a cd of service data, if you're interested I can pop it in my Dropbox
Another thing which might contribute to amplifier failure is users hooking dodgy speakers into the monitor output. I did see one case where guy had managed to run a cable from the monitor output, out to a floor monitor, then back to the satellite box. That went bang!
I have no idea how modern all electronic bingo machines work, in my day it was either rolling wooden balls down a wooden chute, into compartmentalised 'crate' (easily fiddled) or ping pong balls blown up a tube by a blower - also easily fiddled. Either way a good caller can 'steer' the game.
Ron
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