CayMac LC Style Mean Well PSU Replacement

[Fizzbinn]

I purchased a couple of these PCB only boards from CayMac Vintage a while back and wanted to post my build experience.

I ordered the required Mean Well power supplies from Mouser:

IRM-10-12 (12V 0.850A)

https://mou.sr/4gNUPOV

IRM-20-5 (5V 4A)

https://mou.sr/4mXZss7

And planned to make use of a dead TDK power supply (from an original LC) for the case, logic board connector, mains power/switch and fuse holder. All good except for the fuse holder, the TDK 699-0153 power supply's fuse holders have through hole connectors 90 degrees different from what the replacement board needs.

Decided on these, which also seem higher quality than the originals:

Littelfuse Fuse Clips ACS PC 5MM CLIP BRASS/TIN-PLTD

https://mou.sr/48qaT8l

Putting it all together I decided to use the bottom black plastic piece from the original PS, just had to snip off a "fin" that went through the original board next to the largest capacitor. I also put some Kapton tape under where the logic board connector would come close to the metal case but after it was all buttoned up that wasn't really necessary.

I had a little fun making a "POWER UP PIZZA" label with the CayMac logo (@Willj please don't sue!):

Works like a charm, tested in LC, LCIII and Q605!

The only issue I have run into was with my Q605, the hard drive wouldn't spin up. I immediately suspected that it was probably due to the extremely non-standard Seagate Savvio ST936701LC 36GB 10k RPM 8MB Cache Ultra320 drive I was using in there... Looking at its spec sheet it needs 12V 1.58A peak starting current. Interesting that the original Q605 PS (TDK 614-0003) which is labeled as +12V 0.78A can support that (it supported the drive both before and after being re-capped years ago). No big deal as I can use this PS elsewhere.

All in all a fun project! I've recapped several LC power supplies and assembling this was easier in my opinion. Not totally sure about all the relative merits but something about all new components in the original form factor has me liking this approach. I see the boards are currently out of stock, fingers crossed they become available soon for others to enjoy!

p.s. I also purchased and built the IIsi PS version, will post separately on that one soon. Spoiler, it's also nice!

 

[JDW]

Thanks for sharing!

I have a BabyFace PSU for the SE and SE/30 which uses those Meanwell power modules, and what I found was the modules' 5-volt rail quite nearly at 5.0v at the output of the module, but once it reached the motherboard, due to resistivity losses in the wiring, the voltage was 4.9v or 4.8v, depending on upgrades installed. The stock power supplies get around that problem by suppling higher than 5.0v, and there's even a POT inside the SONY model so you can boost it further. The Meanwell modules are sealed though, and offer only a fixed voltage.

I mentioned all that because I'm curious if you measured the 5-volt rail somewhere at the motherboard to determine what voltage level it is. You should measure the 12V rail under load too, but typically the 5-volt rail is more susceptible to large voltage drops than the 12-volt rail is.

 

[Jockelill]

Great feedback! Very interesting with that drive, I figure it's an inrush current phenomena, might be possible to add a power resistor to ease that up a little bit. There are of course also a 15W and 20W model of the IRMs for 12V, but they are slightly bigger in size. When dimensioning these units it was "stay as close to the originals as possible", but since the IRMs have a better (faster) protection circuit built into them, it will of course react on that drive as a "short" and just shut down the output. It might also be that even a 20W IRM would still trip on that drive.