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Lombard heat sink substitute?

P

pudding

Member
I was resurrecting an old Lombard last week that was missing a few bits... all went well but the heat was gone and I couldn't find a replacement down in the basement. I have a feeling there is one down there some where so I am loath to go to the bay and spend just yet. I cut a plate of mild steel, 3/16" by about 1.5" and 3" that fit in the 'pocket' above the processor and starter her up and she seems to run well enough. the temperature above the processor does not go over 98 deg. and at the top most edge tops out at about 112 deg. Fahrenheit (37c/45c) . It is odd to me that the plate is hotter at the top as it is not touching anything.

Can anyone tell me if those are reasonable working parameters for the Lombard processor?


0.jpg
 
Phipli

Phipli

Well-known member
pudding said:
I was resurrecting an old Lombard last week that was missing a few bits... all went well but the heat was gone and I couldn't find a replacement down in the basement. I have a feeling there is one down there some where so I am loath to go to the bay and spend just yet. I cut a plate of mild steel, 3/16" by about 1.5" and 3" that fit in the 'pocket' above the processor and starter her up and she seems to run well enough. the temperature above the processor does not go over 98 deg. and at the top most edge tops out at about 112 deg. Fahrenheit (37c/45c) . It is odd to me that the plate is hotter at the top as it is not touching anything.

Can anyone tell me if those are reasonable working parameters for the Lombard processor?


View attachment 64035
Click to expand...

Grab a copy of Gauge Pro and see what the core temperature is at idle and under load.
 
Phipli

Phipli

Well-known member
pudding said:
I cut a plate of mild steel, 3/16" by about 1.5" and 3" that fit in the 'pocket' above the processor and starter her up and she seems to run well enough.
Click to expand...
By the way, heat transfer in aluminium is about 4 or 5 times better and it won't rust. Copper is even better.
 
M

mdeverhart

Well-known member
I don’t know what the thermal limits of the G3 in the Lombard is, but modern CPUs have a maximum junction temperature (inside the package) of 100C or higher. Commercial grade parts generally have a ~85C ambient temperature limit. I’d say as long as you’re well under 70C you should be ok.

Looking at a picture of the original Lombard heat sink, it doesn’t look like it needed much heat dissipation:
1698004630376.jpeg

The Pismo 400/500 MHz, on the other hand, used heat pipes to pull the heat to a small radiator that had a small fan blowing in it:

1698004708839.jpeg
 
Phipli

Phipli

Well-known member
mdeverhart said:
I don’t know what the thermal limits of the G3 in the Lombard is, but modern CPUs have a maximum junction temperature (inside the package) of 100C or higher. Commercial grade parts generally have a ~85C ambient temperature limit. I’d say as long as you’re well under 70C you should be ok.

Looking at a picture of the original Lombard heat sink, it doesn’t look like it needed much heat dissipation:
View attachment 64041

The Pismo 400/500 MHz, on the other hand, used heat pipes to pull the heat to a small radiator that had a small fan blowing in it:

View attachment 64042
Click to expand...
If they're measuring on the outside / heatsink, their temperature don't directly compare to the temperatures you're mentioning. They're internal die temps that you're quoting.

Plus these crash at a much lower temperature than modern CPUs.
 
P

pudding

Member
Phipli, Thanks, yes I will put Gauge pro on and test it with that. Hope it runs on OS9. And I can chop a piece of 1/4 inch aluminium if I can squeeze that below the keyboard.
 
P

pudding

Member
Well that was interesting, using the app while idling, when measuring the heatsink temperature at 90f/33c the processor was reporting 130f/54c.
 
Phipli

Phipli

Well-known member
pudding said:
Well that was interesting, using the app while idling, when measuring the heatsink temperature at 90f/33c the processor was reporting 130f/54c.
Click to expand...
Yeah, that is how it works. There is a gradient from the highest temp at the core, to a lower temp at the surface, with step changes at any interfaces such as between the CPU and heatsink.

54 is ... Higher end. I'd switch in some aluminium.

Are you using paste?
 
P

pudding

Member
I was re-using the original pad. I will be cutting a chunk of Alu or Copper and adding a wing to transfer the width of the case. Jointing the parts would be easier with copper so that will probably be the way to go. Give the block a good polish and then use new paste, oh yes, and screw it down...

Thanks for all the help!
 
Phipli

Phipli

Well-known member
pudding said:
I was re-using the original pad. I will be cutting a chunk of Alu or Copper and adding a wing to transfer the width of the case. Jointing the parts would be easier with copper so that will probably be the way to go. Give the block a good polish and then use new paste, oh yes, and screw it down...

Thanks for all the help!
Click to expand...
I'd recommend Aluminium. It will last better. (And is cheaper).
 
P

pudding

Member
Maybe you are right. Would you use paste between the block and the spreader? I won't be able to seam weld those together so there will not be good thermal transfer. Regarding cost... I have much scrap material so cost is not an issue. But copper may oxidize faster. I'll post back when it's done and measured. Thanks again.
 
Phipli

Phipli

Well-known member
pudding said:
Maybe you are right. Would you use paste between the block and the spreader? I won't be able to seam weld those together so there will not be good thermal transfer. Regarding cost... I have much scrap material so cost is not an issue. But copper may oxidize faster. I'll post back when it's done and measured. Thanks again.
Click to expand...
Which heat spreader?
 
P

pudding

Member
oh, i was going for a solid lump of 1/8" to 3/16" and attach a thinner wing or 'spreader' to transfer heat away from the solid lump. Vaguely similar to the original parts - but i could go across and into the old drive bay as it is mostly empty now (w/ a solid state drive). Pack in 30 lbs or so of Aluminium - ha!

If only i could 3dPrint aluminium!
 
P

pudding

Member
Yes, but then I would just pay the $75 shipping to Canada for a $7usd part. I'm too cheap for that! ha!

For now I have a grinder, and several remaining fingers...
 
Phipli

Phipli

Well-known member
pudding said:
Yes, but then I would just pay the $75 shipping to Canada for a $7usd part. I'm too cheap for that! ha!

For now I have a grinder, and several remaining fingers...
Click to expand...
Wait, you mean you don't have a CNC in the other room?! :)
 
P

ppcoutlaw

Active member
I have a 333 mhz Lombard that was running hot. The fan ram all the time.
I had some arctic silver cpu paste and a very thin sheet of copper at hand, so I removed the old pad on the heat sink and “glued” three or four carefully cut strips of the sheeting together with the arctic silver.
I put a dab of the silver on the cpu and placed the frankensteined heat sink on top, screwed it all in and fired it up. The fan stopped constantly running. It was a nice result for a sudden case of “what if I did this instead?”
 
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