TX500-Incorrect Component In Kit

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TX500-Incorrect Component In Kit

Postby WG2XKA » 10 Jul 2015 00:05

I recently built a TX500 for another...when powered up, display shows '?????' as model number, it
should indicate 'TX500'.

This problem was traced to the Model Select voltage passed from the main board to display board
on startup, which should be ~1.0 V. It turns out that a 3.3V version of IC8, the logic VR, was supplied
instead of the 5V version, resulting in an incorrect model sense selection (and low rail voltage).

The factory has been notified, and agrees with the problem.

I removed IC8 and replaced with a standard low dropout 3-pin 5V regulator, 78L05,
connected to the appropriate IC pads.

This hack resulted in the rig powering up correctly and working perfectly!

73, John Molnar WA3ETD / WG2XKA
Posts: 4
Joined: 17 Jun 2015 19:40
Location: USA

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