Today at work I was asked to “have a look at that broken amplifier and see if it might be repairable.” When I enquired the symptoms, I was told “well, sparks come out the front when it turns on.”
Reader, this did not fill me with confidence for a prospective repair.

The smell of magic smoke was quite apparent from the start. After removing approximately 84 torx screws (Crown were particularly structurally paranoid on this series, they calmed down on later models), I was able to open the bottom cover. Yes, this generation also has the PCBs mounted upside down, suspended from the top, for some reason.

Two impressions registered in quick succession. Foremost, ‘Christ on a bike, this thing is *packed*’ — the 2U rack case contained about 10 large PCBs, dozens of massive toroidal inductors, electrolytics, and film capacitors, and heat sinks lined with ranks of TO220 packages filling it to the brim, like a miniature model of the internals of the Death Star.

The PCBs were not symmetrically aligned and stacked like 80s lab electronics, when ‘modules’ and ‘slots’ made electrical engineers quiver with zeal in their flared plaid trousers. Nay, they were arranged like Marvin the Paranoid Android had whiled away a small, semi-legless infinity by playing 6-dimensional Tetris with shapes divined by the infinite improbability drive’s most sadistic subroutines. And he had won.

The top-centre-most board of the dense electrical warren was filled with an implausibly large, bordering on comedic, array of 20 large electrolytic capacitors. I choose to believe this was conceived of as a threat to would-be repair technicians, as usually such a formation is used to generate what is technically referred to as “fuck-off high” voltages or currents. I checked I was not touching any metal surfaces inside.

Along with this electronic threat-by-design, the second impression was one deeply familiar to anyone who has ever encountered the product of technology, entropy and time: ‘Well, there’s your problem.’

For among the two aisles of capacitors (220V, 1200uF each), were two, rather worse for wear, standing embarrassedly in the epicentre of a large black blast-mark. When (tentatively) prodded, both fell out to reveal the depth of the damage underneath.

At this point, I opined that a soldering iron would be no more effectual than a tuba in attempting a repair. The patient was deceased. Pushing up the daisies. Died doing what it loved, attempting to become a jacob’s ladder.

The soot from this legendary electrical bucket-kicking was spread throughout the case, and particularly around the case fan, which had valiantly replaced the noxious smoke with fresh oxygen as long as its naive little motor held out.
In addition, thrown in a corner was a smaller film capacitor, apparently literally blasted out of its mounting by its siblings’ explosive death (beside the two disconnected tabs).

After all that, I salvaged some of the boards containing the huge triplicate AC line filter, and the two equally impressive double-ended output channel filters.
It’s certainly clear how different a 2000W-continuous amplifier is to design from one that draws a few hundred watts.

@s0 I want to see this arrangement I need inspiration for my own terrible designs

@maris sadly I forgot to take a ‘before’ photo but it was a crown I-T8000

@grumpysmiffy fairly sure I could chuck a square wave into it and come out with a clean 50hz sine

@grumpysmiffy just checked and the toroidal inductors on the lower PCBs alone (8 total) are worth something like AU$30 each new on mouser.

@s0 Ooh, which Crown model was it? I remember the fun of being inside a Macrotech 5000vz once...

@erincandescent I-T8000. The XTi models are more normally assembled but have a crucial design flaw that slowly kills them unless you replace a set of 8 under-specced 1W resistors right amongst the analogue front-end (something to do with smoothing the low-level analogue rails). One of those things where they spent so long being clever that they missed the wood for the trees.

@s0 Well now we know why the PCBs were mounted upside down: to generate lift from all the exploding capacitors

@s0 this reminds me very much of the failure mode of a graphics card I lost in 2006 that took its AGP port with it to a hot melty place in the sky

@s0 I was so looking forward to hearing more about electronics repair via tuba.

@dredmorbius unfortunately the record has not yet been released internationally

@octo I mean, it worked for a decade plus of uptime, pumping 1800+ watts continuous into massive line arrays so I think it’s ok even if the designers sold their souls to the demon of industrial design

@s0 for whatever reason this thread reminds me strongly of Silicon Chip Magazine's long-running "Serviceman's Log" column :yes:

@ThermiteBeGiants that’s exactly what I was aiming for! I used to go to the local library and collect the whole pile of silicon chips they had and read just that part.

@s0 I spent many a long car trip as a kid reading the annual Jaycar Catalogue from front to back for fun. I have no idea how the doctor came to the conclusion that I was neurotypical

@ThermiteBeGiants ME TOO
When I moved I had to sadly part with my complete annual collection from 2006 to 2017

@s0 This thread is truly magical, quite like the smoke

@s0 You can always turn the amplifier into a pyrotechnics machine, without much effort.

@s0 I had not seen that it was an old publication. I loved the chronicle and the humor with which it is told.

@RileyStarlight thanks :) it was very influenced by the “serviceman’s log” section of silicon chip magazine, which I would sit in the public library and read as a tween. It was similar tales of repair failures and successes.

Sign in to participate in the conversation
Cathode Church

A place for trans makers, coders, tinkerers and dreamers.