Can this amp be salvaged? (Revel B12 / Infinity Kappa)

[Fraser]

Totally agree. It is the OP’s desire to learn from this investigation or repair that prompted my comments to help him. As a commercial repair the unit is definitely scrap as it is beyond economic repair in man hours alone, let alone any modifications required to improve reliability. As others have said, a replacement, better designed power amp module or even a complete new sub woofer unit would likely be a better course to follow if the OP was not keen to learn from this units repair. That said, I have taken on repairs for friends in the past and bitterly regretted it after spending many hours sorting out a real sticker of a design that belonged in the bin ! I learnt from those experiences though  I think the worse was a friends Trio Kenwood TS9xx (TS940?) base transceiver...... lots of failed capacitors and more dry joints than I have ever seen in a unit previously. If you moved any PCB you were likely to cause more failed solder joints. I found out that the particular model was infamous for such failures and was basically a rabbit hole you did not want to enter ! It took me two months of evenings working on it when I had the time and motivation before it was repaired and relatively reliable. I honestly lost count of the solder joints I desoldered, cleaned and resoldered. It was in the hundreds of joints for sure    I gave it back to the friend and told him that I never wanted to see it again and he should sell it while it still worked ! Why did I not give up on the unit as beyond repair ? Well I should have done but he was a good friend and I hate to be beaten. If I had my time again, I would have stopped work on the unit after a week of chasing multiple dry joints and failed capacitors on many PCB’s. The unit is just not worth the effort, even when repaired ! A good lesson learnt though. Did I charge for the work.... nope, I used to repair equipment for free as I liked the challenge and learned a lot along the way.

[EHT]

I know its not as exciting or educational, but I recommend you throw the burnt amp away and just use a standard Class AB external amp which you could pick up cheaply. You couldn't really get a worse environment than being boxed into a subwoofer being shaken to bits with no airflow.

[vmallet]

Update: I cut out most of the black on the PCB after studying what I would have to replace and reconnect. It feels a bit daunting! I also found that the service manual is lying in places What's drawn in the schematic doesn't quite match the board layout a few pages away. Makes it harder to proceed.

I pulled the two big 15,000uF caps to test their time constant in a small RC circuit and they still look good, I'll keep these.

I still need to figure out what to do with the dead inductor. I might try to re-wind it after applying some plasti dip to the areas of the wire where the insulation melted but I'm fearing the result where I would be missing a couple of turns because it wouldn't be wound as tightly as the original.. To be continued

[negativ3]

Christ, I think I can see the event horizon through that black hole 

Keep up the good work, great challenge and learning!

[edpalmer42]

I have a piece of equipment where there was an extensive design change.  Rather than replace the circuit board or add a bunch of jumpers, they abandoned the section of the board where the change was.  A new board was installed above the existing one with stiff wires connecting the two.  Works fine.  This isn't some cheap retail device, it's a cesium frequency standard!

If the inputs and outputs of the damaged section of this amplifier can be identified, the same idea might work well for this repair.  Mount the new board with insulating hardware and drill mounting holes where convenient.

Ed

[shakalnokturn]

I have a piece of equipment where there was an extensive design change.  Rather than replace the circuit board or add a bunch of jumpers, they abandoned the section of the board where the change was.  A new board was installed above the existing one with stiff wires connecting the two.  Works fine.  This isn't some cheap retail device, it's a cesium frequency standard!

If the inputs and outputs of the damaged section of this amplifier can be identified, the same idea might work well for this repair.  Mount the new board with insulating hardware and drill mounting holes where convenient.

Ed

Infinity also made Cesium frequency standards? I bet they take forever to clock...

[XSdB]

Here is a blog I did about repairing this exact issue from 2011:
http://www.cryo-sonic.com/

This article was featured on Hackaday also:
https://hackaday.com/2014/11/13/extreme-repair-of-a-burnt-pcb/


There is also a mod that needs to be done that eliminates the chirp at power on:

change C109 and C132 both to 47uF / 16V / 105 C
and remove R263 from preamp board

There are 3 muting mechanisms in this amp. Line level mute (which part of it serves a double purpose as the limiter), power mute (powers down power amp) and the speaker relay. Initially, all 3 would engage/disengage at different times when going in and out of standby.

 We found that the line level mute did more harm than good for turn on/ turn off transients when everything else is functioning properly. Removing R263 disables the line level mute from engaging during regular use. However, the limiter function is still able to work properly with R263 removed. Also, the line level mute will still function if the sub goes into standby because of a protection issue.