[KL] My adventures with K2600 rack units (continued...)

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This setup allowed me to preserve the standard headers on the fans, and when I tested them prior to installation I promptly blew the fuse. I blew another fuse when trying to read the amp draw. I figured since I was powering the SCSI2SD card with the termination power, I could just install the header in the HDD power connector, so I popped the pins out and installed them in a 4-pin SPOX connector, connected the header and – you guessed it – blew yet another fuse. After all the work I put into mounting this fan I wasn’t going to let it go to waste, so I clipped the fan ends and installed a 2-pin SPOX connector on the 40mm fan and the 4-pin connector on the case fan into the HDD power. No more blown fuses.


After this system was mostly reassembled, as I’m running the diagnostics and looking things over I noticed the two 7805 VRMs on the audio board were hot, way too hot. I looked at this as an opportunity for improvement. I first looked at the small TO-220 heat sinks I had around, but even after clipping the support lead it was just too tall for this application, and I had my doubts about the spacing. Then I remembered the set of Thermaltake chipset heatsinks that came with the RAM heat spreaders I bought some years ago, just sitting in a drawer. I pulled one out and at 58mm, they were way too wide for this application, but the 20mm height was just about perfect. I cut it in half:
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 spent several minutes with a product called “Goof-off” and some paper towels to remove the adhesive. There are two of these per kit, and only one had the adhesive; a fact I wish I had been aware of earlier. I squared the heatsink against the VRMs and marked off the centers of the mounting holes. I then used a nifty little combination drill and tap set, the smallest bit of which was an M3x0.5. An application of penetrating oil and the “three steps forward, one step back” tapping process and I had a pair of nice M3 mounting holes in the heat sink.
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I could have probably left the heatsink as is at this point, perhaps even slightly countersinking the opening for deburring purposes, but if you’re familiar with the application of heatsinks, you know one needs to have as smooth a mating surface as possible for maximum heat transfer. So I used some 440-grit sandpaper (hey, it’s what I had on hand) and smoothed the cut end and hone the surface. I finished this up using a sheet of cheap office paper to produce a surface much better than the original.
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Applying some Noctua NT-H1 thermal paste to the heat sink, using that to hold a mica insulator in place and a dab of the paste on it provides good heat transfer while the mica insures insulation between it and the transistor’s ground. A nylon bushing and M3 screw completed this little operation.
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And this little project is complete.
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As I’m buttoning this up, I got the idea I’d like to try my hand at sleeving the power supply cables in paracord. This came from my research into wrapping the ribbon cables in PET sleeving, and I’ll be completely honest here and say it serves no purpose other than vanity. So I pulled the main power supply cable from the CPU board since it was the only one not twisted and began the process. Using a small common screwdriver, I carefully pried up the plastic tab which allowed the pin to unlock and slide out. I knew I had to coat the pin in something to keep it from snagging the cord, so I used some heat-shrink tubing to cover the pin and allow it to slide down the cord. I cut the paracord to length and removed the nylon cores, then slid the pin into one end. inchworming my way down. Once I had the jacket about halfway on, I slid smaller pieces of heatshrink over it to seal the finished ends after removing the heatshrink cap.
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I got lucky with my first two cables. On my third attempt, one end started fraying as I was almost complete. So for the remainder, I used a lighter to melt the ends and the expansion of scissors to expand the opening, a lesson I must not have taken to heart with all the PET sleeving I did earlier.
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All I had to do was keep them in place, so I used some nylon thread to stitch the cables together at several points along the length, and this little project comes to a close.
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Yeah, I know; this serves no really useful purpose, but I gotta say – it sure looks cool! Now all to do is go through the diagnostics one last time to verify installation and access to the RAM:
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The PRAM:
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The ROM installation:
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And finally access to the SCSI2SD devices:
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So, after all this, what’s next? Really, what’s left is a better question. I wouldn’t mind replacing the displays with a white-on-black LED versions. The PSU could stand to have the 220uf C6 capacitor replaced with a 100uf cap, per Kurzweil’s recommendation, and if I’m in there I’d probably replace that variable resistor R9 for the +12V adjustment with a 100K precision multi-turn pot.



Having worked on a K2000, a K2500 and now a K2600 series, I can see the progression. All along the K series, Kurzweil built these things like tanks. Some of the things like the volume/headphone board are just common from the K2000 series (says so right on the silkscreen). But other things like the mounting tray for the audio I/O board – it’s about time.


A big shout out to Alex Goetsman – dude, you always do manage to come up with the stuff.