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IBM 5150 motherboard  -  Component temperature

NOTE:

Temperatures shown below are crudely indicative only. See note 1.

NOTE:

Only sometimes (repeat: sometimes), are faulty chips very signifcantly hotter than normal. It depends on the nature of the fault (the failure mode).

The heat image and other readings were taken:
• using a HIKMICRO Pocket2 thermal camera; and
• after the motherboard had been powered on for about an hour.

A power supply is the only thing connected to the motherboard.

Ambient temperature (i.e. temperature of surrounding air) was about 18° to 20° Celcius.

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16KB-64KB:  One of my IBM 5150 motherboards of type 16KB-64KB

BIOS Revision:  10/27/82

In decending temperature Intel D8284A:  About 59° Celcius Intel P8253-5:  About 47° Celcius U94 (SN74S280N):  About 47° Celcius Intel P8255A-5:  About 45° Celcius U95 (SN75477P):  About 45° Celcius  (See note 2 below) U8 (F74LS245PC):  About 44° Celcius Intel P8259A:  About 43° Celcius Intel D8088:  About 43° Celcius Intel D8237A-5:  About 41° Celcius Cassette BASIC ROM's:  Per the photo at here, U30 on this particular motherboard has a different package type than the other ROM's

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64KB-256KB:  One of my IBM 5150 motherboards of type 64KB-256KB

BIOS Revision:  10/27/82

In decending temperature AMD P8237A-5:  About 60° Celcius  <------ !!!!  About 20 degrees higher than on the 16KB-64KB motherboard above Intel D8284A:  About 54° Celcius AMD P8253-5:  About 54° Celcius AMD P8255A-5:  About 50° Celcius U94 (SN74S280N):  About 50° Celcius AMD P8259A:  About 46° Celcius AMD D8088:  About 46° Celcius U8 (SN74LS245N):  About 43° Celcius Cassette BASIC ROM's:  Per the photo at here, the four Cassette BASIC ROM's are AMD made. Is AMD's design the reason for the heat?

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Note 1	• Do an Internet search for factors that affect temperature readings on a thermal camera. • The surrounding air temperature is expected to affect chip surface temperature. • Different makes of a chip could emit different levels of heat (because the circuitry inside the chip might be different). • Due to the motherboard design, the same make-model of a chip in socket {XXX} could emit a different level of heat to that in socket {YYY}.
Note 2	A very different result to my 64KB-256KB motherboard.  The cause may be related to input pin 7. My particular 16KB-64KB motherboard  : pin 2 = LOW, pin 7 = HIGH My particular 64KB-256KB motherboard: pin 2 = LOW, pin 7 = LOW The 75477 is an open-collector driver. Pin 7 controls the open-collector transistor associated with the speaker, but there is no speaker connected to the motherboard. Hypothesis: Pin 7 being HIGH is turning on something in the chip, drawing significant power.