hp proprietary uP history (9825 uP?)

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed May 5 18:39:11 2004

> try it out just for kicks. Imagine my surprise when it worked! I've
> probably found 30 or more surplus 9825s over the years and I don't think I
> ever found one that didn't work.

The 9825 (and for that matter the 9815 which has much the same design of
PSU) does have one problem, though. The 5V PSU is a switching regulator,
and there's no corwbar fitted (no idea why not, the older 9810 and 9830
have crowbars on all the important PSU outputs, so HP certainly knew about
such things). If the chopper transistor shorts, then 5V line will leap to
about 25V. Needless to say this wipes out the entire set of ICs... The
9845, with a mains-input SMPSU (not the low-voltage non-isolated switching
regulator of the 9815 and 9825) doesn't suffer from this.

I must design a crowbar and add it to my machines sometime. Hopefully
before the transistor fails.

-tony
Received on Wed May 05 2004 - 18:39:11 BST