--------
In message <[email protected]>, Pe
rry Sandeen writes:
>OK, but why? The temperature would be stable so the resistorsand
>reference diode wouldn't drift.
No, the temperature is not stable, not even close.
Given that the TL431 is quite good at measuring temperature, that
makes it unsuitable in this case.
I have identified one source of the temperature fluctuations: The
series pass transistor of the +20V rail is located right beneath
the A15 PCB, so any variation in mains (or EXT DC) voltage causes
the A15 temperature to change accordingly.
More details here:
http://phk.freebsd.dk/hacks/HP5065A/20150903_psu/
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
[email protected] | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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