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HP42S with non-volatile ram
09-28-2020, 02:41 AM
Post: #5
RE: HP42S with non-volatile ram
The schematic pinouts are incorrect, he indexed the wrong corner of the tab package as pin 1 so go by the pictures, not the schematic.

The other issue is where he mounted the SN74LVC1G97. When mounted on standard thickness proto boards, the chip will be pressed into the metal esd plate attached to the case back. This can lead to fractured solder connections with the chip in compression.

On my installs, I thinned (sanded) the proto board down to about 0.5mm and mounted in the area where the second 17B rom would live so that the chip fits within a recessed area in the esd plate. That results in no pressure on the solder connections. It also provides easy access to VCC and gnd connections, they’re right there on the unused pins 14 & 28.
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Messages In This Thread
HP42S with non-volatile ram - GreyUser - 06-11-2020, 04:40 AM
RE: HP42S with non-volatile ram - mfleming - 06-11-2020, 02:26 PM
RE: HP42S with non-volatile ram - lyuka - 09-26-2020, 12:12 PM
RE: HP42S with non-volatile ram - GreyUser - 09-28-2020 02:41 AM
RE: HP42S with non-volatile ram - lyuka - 09-28-2020, 01:13 PM
RE: HP42S with non-volatile ram - GreyUser - 09-29-2020, 01:41 AM
RE: HP42S with non-volatile ram - lyuka - 09-29-2020, 09:48 AM
RE: HP42S with non-volatile ram - lyuka - 11-17-2020, 06:11 PM
RE: HP42S with non-volatile ram - G-SAN - 02-06-2024, 03:54 PM



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