25 Aug
2014
25 Aug
'14
5:57 p.m.
See this one I knew, so yes, I did check the zener regs, and yes, they are
just fine.. as is the 7805.
Nods on the 7805s running hot on this machine. Might be a nice place to
install a modern part with higher current handling, and a bit more heat
sink as well.
Whatever was getting po'd by my little polarity 'oops' was on the D/C
board.. and so far, I can't find anything that obviously went wrong. I did
note that the 7490 counter was running +uncomfortably+ hot in general, so I
dropped-in another NOS part.
FWIW, all of this is done on a variac.. so nothing runs at full AC line
unless needed, and nothing needs to fail in a spectacular way. I hate
electronic fires, they reek and they're unnecessary.
On Mon, Aug 25, 2014 at 5:49 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
On 2014-Aug-24, at 8:56 AM, drlegendre . wrote:
Then I caught a slight whiff of "that"
smell, and switched-off, to hunt
On 2014-Aug-24, at 2:50 PM, drlegendre . wrote:
Anyway, it was getting very late, and I'd
been at it for over eight
hours.
I'd accidentally swapped the +18 & -18
lines, and that was causing the
excessive current & heat.
The 8080 uses +12 & -5, both of which are derived from the +/-18 lines
through discrete zener-diode-&-series-resistor regulators.
Those regulator components may have been the source of the burning smell.
Hopefully the forward-biased zeners clamped the bad voltages and saved the
8080, but you should ensure that those regulator components are within spec
and still functioning properly. If the regulator components got as far as
burning enough to smell them, it may be a good idea to replace them.