Extra cooling in LCs?

[InuNacho]

I'm going to FrankenMac my old LCII with a dead PSU with a working one from a donor LC. Back 20 years ago the LCII kicked the bucket because the Speedster 040 card I had installed caused overheat issues. Fast forward today and I'm looking at adding some kind of extra cooling to the LCII to ensure it doesn't kill itself again.
I have the small square hole open on the back and am thinking of squeezing a small fan in there to pull heat out. Alternatively I was thinking about my Mac Pro where it pulls air in the front and pushes it out the back. Because the LC series is slightly elevated, does it seem like a good idea to reverse the bottom fan to suck air in and have it come back out the rear?
Another idea I had was entirely replacing the old fan and installing a newer faster/efficient one and possibly re-areanging the speaker to be another fan.

Any opinions or ideas?

 

[MacTech68]

Many of the old LC 'pizza box' power supplies probably need capacitors replaced by this age. Switches on some were also failing years ago too (IIRC).

I recall that the proper LC475/Quadra605 power supplies did have a slightly higher output Wattage which may help if you decide to add the 040 card back into the machine. I'm not sure how the higher wattage output PSUs have fared over time, compared to the lower wattage PSUs.

Here's how they originally shipped - as you can see, The LC, LCII & LCIII could use the LC475 PSU.

LC LC II 661-0594 Assy 699-0153 replaced by 661-0787 then 661-1733 (25.625W)
ASTEC Model AA16250 asy 699-0153
+5v 3.25A
-5v 0.075A
+12v 0.75A
&
TDK Model 699-0153
+5v 3.25A
-5v 0.075A
+12v 0.75A


LCIII 661-0787 Assy 614-0003 replaced by 661-1733 (25.985W)
ASTEC Model AA16251
+5v 3.25A
-5v 0.075A
+12v 0.78A
&
TDK Model 614-0003
+5v 3.25A
-5v 0.075A
+12v 0.78A


LC 475 661-1733 36W Assy 614-0028 (36.125W)
ASTEC Model AA19140
+5v 4.75A
-5v 0.075A
+12v 1.0A
&
Dyna Comp Inc Model DCF-353
+5v 4.75A
-5v 0.075A
+12v 1.0A


As for adding a fan, It probably depends on where the heat is being generated. Most (but not all) LC pizza box PSUs had holes in the casing of various designs (depending on the manfacturer eg TDK, Astec, Dyna Comp). If the PSU has many holes, you may want to place a fan such that it can directly draw air thru the PSU.

The side of the top cover should have some slots that are open which air could be drawn thru.

One other thing about fans is if you go for a higher CFM, you may reach a threshold where you try to draw more air thru the case than the air gaps allow which will cause notable sucking noise. You could then experiment with a series resistor to find a voltage for the fan where the added noise is acceptable or reduced.

If the 040 CPU is the hottest part, a thin CPU fan (height permitting) could be fitted to blow onto the CPU and/or it's heatsink.

That's my input - no doubt you'll get plenty of others

 

[InuNacho]

Wow thanks for that info, had no idea that the PSUs were different in the different revisions. Looking around on ebay there are a few small USB powered fans that I can easily put here and there. I noticed on the lid theres a giant piece of metal, is that just RF shielding or does it act a giant heat sink?

 

[MacTech68]

...is that just RF shielding or does it act a giant heat sink?

RF shielding.

 

[InuNacho]

RF shielding.

Awesome, I can remove that to get some proper work done inside of it.