Re: Compaq PDP-121P - Baked MOV
Looking that the datasheet schematic of LM339N, it doesn't look like there should be any resistive path between the positive input and VCC, on a comparator.
On the daughterboard PCB (voltage protection board?) there is a 10K resistor across VCC and positive input pin 5
But 5K is measured across it's leads, in-circuit
Looking at my photo, the only path that could provide this lower resistance is through the chip.
So, if my thinking is correct, either there is a problem with the chip, or the resistor
The fact that it measures 5K (a too coincidental value) makes me suspect that i'm missing something, and that it's meant to be like that
There is also the same thing happening across another resistor in the photo (just underneath it).
Also, the 12.8V rail doesn't go to the daughterboard
Looking that the datasheet schematic of LM339N, it doesn't look like there should be any resistive path between the positive input and VCC, on a comparator.
On the daughterboard PCB (voltage protection board?) there is a 10K resistor across VCC and positive input pin 5
But 5K is measured across it's leads, in-circuit
Looking at my photo, the only path that could provide this lower resistance is through the chip.
So, if my thinking is correct, either there is a problem with the chip, or the resistor
The fact that it measures 5K (a too coincidental value) makes me suspect that i'm missing something, and that it's meant to be like that
There is also the same thing happening across another resistor in the photo (just underneath it).
Also, the 12.8V rail doesn't go to the daughterboard
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