8501 power consumption

From: Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de>
Date: Sun, 12 Feb 2012 18:05:59 +0100
Message-ID: <4F37F177.3030508@laosinh.s.bawue.de>

since everyone says the 8501 CPU has a high failure rate due to 
overheating, I did some measurements by lifting Pin 5 (Vcc) from the 
socket and using an Amp meter set to 200mA between it and +5V to see how 
much power it really needs. The measurements were taken with the system 
sitting idle at the welcome screen after waiting for about 30 secs for 
the chip to warm up (power consumption goes down).

The results:

7501R1 datecode 2684:    85mA

8501R1 datecode 4184:   108mA

8501R4 datecode 4986:   109mA

To compare against a CPU that is not known for a high failure rate:

6510   datecode 2784:    96mA

The surprise was that the 7501 uses about 23mA less than the 8501, I 
would have expected the opposite.

In any way, even the 109mA translate to at most 545mW the chip has to 
dissipate. That's well inside what a 40pin DIP IC can handle, it's 
nothing that would cause it to overheat, the 6569-VIC in a C64 runs much 

Unless there is a hotspot on the 8501, overheating can't be the reason 
for the high failure rate of this CPU. Still, a heatsink will cause the 
die to run cooler and slow down whatever causes the failure.


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Received on 2012-02-12 18:00:05

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