MQFP 7136

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MQFP 7136

Unread postby Kimmy » Tue Jan 10, 2017 5:29 pm


Quick question(s) - Should a 7136 (aka 7106) ADC have the same voltage at the in_hi and in_lo pins when referred to analog common with 0V input?

About a year and-a-half ago I soldered a MQFP 7136 to a TH adapter board, found it excrutiatingly hard, but on first appearances it was functional, I dread to think how hot it got with the palliative solder wick time cleaning up solder lagoons and bridges between pins..., as the circuit was no use as a milliohmeter I made another that worked and put the useless prototype in a box, until yesterday, and only then measured the voltages on the pins.

AFAIK all components like capacitors are correct, they all appear to be in good condition (measured); wiring: checked three or more times - all is correct; power supply voltages are correct; ref voltage is correct; oscillator frequency correct; input voltage reaches pins in_hi and in_lo correctly. However, the LCD numbers just float around randomly, LCD doesn't settle to 000 and has no output read-out with a valid input, still just drifts through its random routine of, e.g.: -002, 002, 007, 154, 1632, 74, 009, etc.

In_lo to analog com (measured at the IC pins) reads about ~2.5V, in_hi to analog com measures 0V - that's bad, right? Shouldn't both read the same value (~2.5V, in this case) when referred to analog com with 0V input? I'm assuming I've burnt something internal to the ADC as I can find no other fault or mistakes - is that a possible reason?

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