Blast City PSU and Amp Cap list / recap project

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    • Blast City PSU and Amp Cap list / recap project

      My blast is struggling to keep up on voltage, so I decided it was finally time to try recapping it. I have done a lot of single cap replacements and rom swaps etc but never a full recap so this should be fun.

      Please correct me if I am wrong on any of the types/tolerances, and I do need help verifying my identifications of a few caps as noted below.

      Audio Amp PCB Cap List (Complete list)

      Electrolytic Aluminum caps (KME series, +/- 20%. KMG series on digikey is recommended replacement by manufacturer.):

      C1,C2 - 35v 4700uf
      C3,C4 - 50v 100uf
      C13,C14,C15,C17 - 50v 10uf
      C16,C18,C19,C20 - 50v 2.2uf
      C21,C22 - 50v 1uf
      C23,C25 - 50v 33uf

      Disc cap (ceramic?):

      C9,C10 - 220pf +/- 5% (I think. Marked as 221J. Would like confirmation.)

      Brown (polyester film cap?) These are all the same:

      c24,c26,c11,c12,c8,c7,c5,c6 - 0.1 uf (cap marking is 104 with 3 dots around the 4. There is one dot above the 4 and two dots below it. I would like confirmation on these)

      ----

      PSU PCB Partial Cap list (missing disc caps)


      Electrolytic Aluminium caps (KME series, +/- 20%. KMG series on digikey is recommended replacement by manufacturer.):

      C25 - 25v 100uf
      C31,C39,C40 - 10v 6800uf
      C24 - 16v 2200uf (I think this is c24... marking was partially blocked by the white stuff used to secure some caps)
      C36,C44 - 50v 0.47uf
      C16,C11 - 50v 10uf
      C12 - 50v 1uf
      C14 - 35v 47uf
      C20 - 35v 22uf
      C5 - 200v 820uf (The huge one. This one is marked (M) not KME, please let me know if this is of any significance.)

      Nichicon Radial film caps(?) These are a greenish color, marked 104K 1HL. My best guess is 0.1uf 10% for all of these:

      C33,C28,C4,C48,C18,C8,C9,C47

      Nichicon Radial film caps(?) These are a greenish color, marked 223K 50H. My best guess is .022uf 10% for these two:

      (forgot locations, will update)


      Questions / To Do before I start:

      Should I even bother replacing the brown / green film caps if my PSU was working but just weak? Or just start with the electrolytic caps and see where that gets me?

      Any advice in particular for the big ass 200v 820uf cap on the PSU? Should I short it with a resistor before I take it out?

      The post was edited 2 times, last by skate323k137 ().

    • skate323k137 wrote:

      Should I even bother replacing the brown / green film caps if my PSU was working but just weak? Or just start with the electrolytic caps and see where that gets me?
      I wouldn't bother with the film caps. electrolytics have a compound that deteriorates when exposed to oxygen so when the rubber seal weakens it starts breaking down the chemicals inside and kills the cap. That's why they bloat and leak when they go bad and why heat cycling (and other conditions that can weaken seals) cause them to fail in 15 or so years. Film caps don't have that problem because they're constructed differently. That's not to say they can't go bad but the conventional wisdom seems to be that even the worst of them will last 50+ years.

      I've never seen a cap kit that replaced anything other than the electrolytic caps unless it was a known high failure component on a particular pcb. Most don't bother with the big filter cap either, though I think that's mostly a cost/availability thing. They're expensive and uncommon enough that you're better off not replacing it unless that one specifically needs to be replaced.
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    • Finished the recap today. PSU is a pain because of plated thru holes. Amp is pretty easy aside from the large ground planes acting as heat sync.

      The sound amp wasn't a drastic improvement, but it did clean up interference I had previously when the cabs volume pot was above half.

      Power wise, no more struggles. Running a NAOMI fine now at 5.1/3.35 at the system (001 loom) without maxing the PSU pots. prior to recap, maxed pots still only got me 4.9 / 3.2 ish.

      Main improvement I noticed is it cleaned up the video. It looks like I did monitor work or something, it's that noticeable.

      P.S. @codecrank, the AO wiki is missing:
      C16,C18,C19,C20 - 50v 2.2uf
      on the sound amp
      (Edit, I realized I could log in so I added them)

      P.P.S. thanks for putting that in the wiki. I printed it off and used it as my checklist.

      The post was edited 1 time, last by skate323k137 ().

    • twistedsymphony wrote:

      skate323k137 wrote:

      Should I even bother replacing the brown / green film caps if my PSU was working but just weak? Or just start with the electrolytic caps and see where that gets me?
      I wouldn't bother with the film caps. electrolytics have a compound that deteriorates when exposed to oxygen so when the rubber seal weakens it starts breaking down the chemicals inside and kills the cap. That's why they bloat and leak when they go bad and why heat cycling (and other conditions that can weaken seals) cause them to fail in 15 or so years. Film caps don't have that problem because they're constructed differently. That's not to say they can't go bad but the conventional wisdom seems to be that even the worst of them will last 50+ years.
      I've never seen a cap kit that replaced anything other than the electrolytic caps unless it was a known high failure component on a particular pcb. Most don't bother with the big filter cap either, though I think that's mostly a cost/availability thing. They're expensive and uncommon enough that you're better off not replacing it unless that one specifically needs to be replaced.
      So about that big ass filter cap (200v/820uf), finding a replacement was pretty easy. I just measured the diameter and lead spacing and put those in my search params at digikey.

      I did replace it but I would caution anyone else to be very very careful with it. The shape of the snap-in leads will rip out the through hole plating on the PCB if you remove it carelessly.