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Recapping DBX 900 Modules
Old 12th October 2018
  #1
Gear Addict
 
hourglass's Avatar
 

Recapping DBX 900 Modules

I have a handful of DBX modules that have gone "thin." They lack bottom end, so I suspect they need new caps.

Can anyone who has recapped a DBX902 or a Dynafex MC101 let me know which caps generally go bad on these? I'd rather not be shooing blind and replacing ones that don't need to go.

I certainly COULD pull each cap and put them, one at a time, on my cap tester, but I don't have time for that. I barely have enough time to buy and hookup new gear, let alone ever get to the fixer-uppers that are constantly littering the back shelf.

Thanks for any help!

Ryan
Old 13th October 2018
  #2
Gear Maniac
 

I haven't worked on them but a quick glance at a schematic suggests that I'd be looking at C7/C8 which are both 4u7F 25V non-polarised electrolytics. If they get dry, they will create a 2 pole HPF higher than you'd like to hear!
C23 is the same component though may be less critical but for 20p you may as well change that too.
Others worth changing might be C9/C12. 22uF electrolytics that seem to be output push-pull bootstraps but I'd need to stare at it longer to work out their proper purpose.
Older electrolytic capacitors, whatever their purpose might need attention after a decade or 2. It's worth replacing any other electrolytics that are power filtering while your soldering iron is switched on. (C24/5/6/7)
Old 13th October 2018
  #3
Gear Addict
 
hourglass's Avatar
 

Holy cow! Thanks so much for taking the time to look at the schematic and post a reply. That's exactly the info I was hoping for.

Ryan
Old 4th November 2018
  #4
Quote:
Originally Posted by hourglass View Post
Holy cow! Thanks so much for taking the time to look at the schematic and post a reply. That's exactly the info I was hoping for.

Ryan
Hourglass how did it work out? I have had great success recapping to increase the low end. I typically buy a second duplicate module/synth and experiment on that one. When I replace the largest capacitor I keep the same uf value but higher voltage rating. However, the second largest capacitor I had great success replacing with a higher uf (the tolerance is 20% anyways). The bass low end opened up and the difference was phenomenal on my mixers and effects units, not so much synths interestingly. I had one effects module for 20 years that I never used because it was shrilly and decided enough is enough I should experiment, it's cheap anyways. If I kill it then so what. And the result was so great (low vibrating ultra bass) that I bought another unit to make the same modification. I never in my wildest dreams would have imagined myself buying a second VF-1. Todays circuit boards are too crowded and have SMDs, so it's not possible to do the same mod, but you can mess around with older cheap equipment if you feel comfortable and accept the consequences. I recapped everything in my studio and only messed up 1 unit for good (which I have another two of anyways), it was my first experience replacing SMDs and I over confidently (and naively) thought it would be as simple and easy as the through hole capacitors.
Old 4th November 2018
  #5
Quote:
Originally Posted by hourglass View Post
I have a handful of DBX modules that have gone "thin." They lack bottom end, so I suspect they need new caps.

Can anyone who has recapped a DBX902 or a Dynafex MC101 let me know which caps generally go bad on these? I'd rather not be shooing blind and replacing ones that don't need to go.

I certainly COULD pull each cap and put them, one at a time, on my cap tester, but I don't have time for that. I barely have enough time to buy and hookup new gear, let alone ever get to the fixer-uppers that are constantly littering the back shelf.

Thanks for any help!

Ryan
If limited in time then replace all the caps on the PSU all in 1 go. Before unscrewing the unit heat up the desoldering iron AND soldering iron. Once you've finished removing the PSU card they should be hot enough so you can get started. Replace one capacitor at a time, and once done then you can turn off the soldering and desoldering iron, and plug in the unit. Keep your hands and face away from the circuit board when you plug it in, and be prepared to turn it off quickly if you messed up. If it powers on without any capacitors blowing up (this means you put it in the wrong way) then test the sound outputs. If it sounds good and you are happy then screw it all back together. If not, then oops you did something wrong. Go back and fix it.
Old 11th November 2018
  #6
Here for the gear
 
terryaudio's Avatar
 

Make sure the caps you use are unit appropriate!

Oddly, Xicon makes a good NP electrolytic if needed. Recommended.
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