26 Aug
2010
26 Aug
'10
2:17 p.m.
On 2010 Aug 26, at 1:45 PM, Tony Duell wrote:
The capacitor in question is the 680uF unit on the output side of the
+15V regulator. The regulator (723) is configured with current
limiting.
Someday I'd like to remove the cap and measure whether it is actually
providing any C to the circuit after years of reverse polarity
operation. The cap is rated for 25V, I wonder whether there is a
threshold effect on 'lytic caps, where -Vapplied < fraction*Vrated is
not damaging to the cap.
Maybe HP's
QC isn't quite what we like to believe it to be. I've
MAybe not... I think I've had the odd reveres small electrolytic too...
mentioned in the past an HP9815 calculator
(1970's) in which a power
supply filter electrolytic capacitor was factory installed with
reverse
polarity. It has never presented a problem however, so in that
instance
I didn't correct it, just noted it in my log for the machine.
Now that I would _certainly_ replace. The reason is that the 9815 (and
9825 for thatr matteer) do not have corwbar cirucits in the PSU. If the
PSU malfucntions in the 'right' way -- e.g. the chopepr transistors
shorts (on the heatsink on the side of the transforemr box), the 5V
line
ca jum pt abotu 30V. Needless to say that's expensive...