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A 'once and for all' declaration regarding L88M mask MC68040 CPUs

VWGuy

Member
I'm just looking for a later .57 um mask at this point. The seller refunded my fake with no hesitation. They know what they are doing and don't care.
 

jessenator

Well-known member
I simply don't want the thread to derail. I want to keep this, as much as possible, about the thermal properties and debunking the bull$#!@ claims that have been parroted since time immem—no maybe the last 20-25 years or whatever the window is. There is a dedicated thread to fake chip ID, well, specifically 040s in this case… but at any rate, (clear) photos of fakes are welcome there for sure.

I know I sound like a broken record, but what I want is thermal imaging evidence/record of the properties of 040 packages, L88M most of all at this point.

From what I've seen and tested, minus the effects of the well-documented XC errata, is there any point in fawning over the L88M when another mask revision will perform just as well? I would say no. An E42K will perform just as well. Perhaps in situations where heatsinks aren't used there will (definitely) be issues, but IMO it's just flexing and !@#$ measuring at this point. Finding a genuine non-LC 040 in itself is a win anymore. With a proper heatsink, most that I've tested can go to 40MHz without adverse effects thermally. I think what I might do, if ever spare time wills itself into being, is do general system stability tests (in another thread).

Also, VWGuy, while warning about things like this is important, something that I find is valuable, it's a gray area as far as forum rules are concerned. While in the trading post section, it sure should be globally applicable, basically it's that we don't engage in ebay seller/buyer feedback or commentary—unless that rule has changed in my absence 🤔 Anyway, I'm not a mod, but it's one of my neuroses, so apologies for calling out. It might be something to consider in the improvement/topics thread coryw set up.
 

VWGuy

Member
What kind of heat sink are you running during these tests? My current chip (early 25 mhz) runs hot enough I can't barely touch the sink.
 

rplacd

Well-known member
Last I checked, Herb was out of stock.
If anyone has a spare they'd kindly let go? I am doing a scratch built Amiga 4000 from bare motherboard and accelerator card.
Herb just restocked! I purchased one... although there isn't many, Herb had to get the pins repaired. Hence why I posted here. Herb's an amazing detective for this stuff.
 

rplacd

Well-known member
Finding a genuine non-LC 040 in itself is a win anymore. With a proper heatsink, most that I've tested can go to 40MHz without adverse effects thermally. I think what I might do, if ever spare time wills itself into being, is do general system stability tests (in another thread).
I would love to hear your advice on proper heatsinks! I have an (evidently) non-genuine '040/40 that's unstable at 40 MHz. It reports to have both FPU and MMU, but I've stuck a cheap Amazon heatsink and it overheats and barfs. Would you have a link to a proper heatsink?
 

David Cook

Well-known member
I would love to hear your advice on proper heatsinks! I have an (evidently) non-genuine '040/40 that's unstable at 40 MHz. It reports to have both FPU and MMU, but I've stuck a cheap Amazon heatsink and it overheats and barfs. Would you have a link to a proper heatsink?

Double-check that the heatsink's adhesion is actually thermal. I've received heatsinks from Amazon sellers with ordinary double-sided sticky tape as well as 3M coated tissue tape (not thermal tape). That will act as an insulator, which is the opposite of what you want.

Thermal-pad-versus-tissue-tape.jpg

In the picture above, I peeled off the tissue tape, cleaned the part with isopropyl alcohol, and applied a ThermalRight thermal pad.
 

rplacd

Well-known member
Double-check that the heatsink's adhesion is actually thermal. I've received heatsinks from Amazon sellers with ordinary double-sided sticky tape as well as 3M coated tissue tape (not thermal tape). That will act as an insulator, which is the opposite of what you want.

View attachment 41870

In the picture above, I peeled off the tissue tape, cleaned the part with isopropyl alcohol, and applied a ThermalRight thermal pad.
Hey, thanks for the recommendation! I've just looked it up, and I've just noticed that you can get this stuff in multiple thicknesses. Would you have any recommendations/knowledge on why this is the case/what to get?
 

jessenator

Well-known member
What kind of heat sink are you running during these tests? My current chip (early 25 mhz) runs hot enough I can't barely touch the sink.
All the tests were with no heatsink at all.

This is not aimed at you, but you bring up a good point:
The myth-to-be-busted "cool to the touch", by implication is "it doesn't need a heatsink." If "cool to the touch" was intended to be applied to a thermal-managed CPU, it would be a moot point, IMO. Get a larger, more efficient heatsink: problem solved. (A resourceful individual could certainly find something even 25 years ago.) The thermal solution …solution isn't a qualifier here; the original intent of the saying was "this [L88M] is the coolest-running 040 there ever was; you could run it without a heatsink and it would run cool to the touch." regardless of over/under- clocking. If thermal management was a qualifier, I could just rig up a liquid cooling solution, or even some LN2 and say that even my D50D runs cooler than an L88M, and I'd be objectively correct!

Have we proved the first point? Yes, you can certainly run certain 040s (from the Wombat onward) without a heatsink and unless ambient temp is quite high (my tests it was in the 20s C somewhere), the package temps, save one, never reached 100C which was the Motorola thermal design test. In the one test further back in the thread, I cut it off before it hit 90C, and the D50D I couldn't get higher, because it refused to post after a certain clock speed.

Have we proved the second point? Absolutely not.


I hope I don't seem like I'm getting heated here. I'm not trying to call anyone out, either, I'm simply trying to stick to the premise, because I'm ruddy great pedant! :ROFLMAO:

Do I think heatsinks are a good idea? Abso-FRIGGIN-lutely. Whatever fits in for the final application, use it! I just hold that heatsinks have nothing to do with the myth to be busted.
 

MrFahrenheit

Well-known member
For heat sinks for these, I do a border of thermal tape, avoid 1/4 inch, all the way around. Then I apply a pea size of thermal paste, like Noctua, in the center and the thermal tape holds the heat sink down.

By using only a border of tape, it can be removed if necessary, easily, and yet it holds down securely.
CC98384B-5F21-4836-B155-A569D4F3CEB5.jpegBDB8897E-4044-4E5A-B025-F7BFCFE84940.jpeg
 
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