9 May
2023
9 May
'23
7 a.m.
On 2023-May-08, at 11:24 PM, Rob Jarratt via cctalk wrote:
Yes, this was acknowledged. I was explaining how it might have been the source of the
mystery 0.08V, so if/as it's not then here's another possibility:
It's conceivable there is an oscillation being generated around this -12V output
circuitry, perhaps by a bad semiconductor junction or because some of the junctions are
operating in reverse to normal under the test setup in conjunction with the caps and
inductors, the mystery voltage being generated in consequence. Have you poked around the
-12V area with a scope, as opposed to multi-meter V measurements?
I am going to read your answer more carefully later. But I wanted to check one thing. I
measured the base-emitter voltage as negative in both cases, and yet the TIP121 appears to
be conducting on the bad PSU. Surely that means that the TIP121 is not working correctly?
The TIP121 would/could be conducting because under your test setup with no VStart-12
it's biased in the reverse-from-normal direction and could be conducting in reverse
through the BC junction. The 0.016V across the 10Ω R from C-to-GND is nonetheless higher
than would be expected from the trickle current available.
Which brings me to this, in reply to earlier message:
On 2023-May-08, at 5:03 AM, Rob Jarratt wrote:
From: Brent
Hilpert <bhilpert(a)shaw.ca>
From earlier measurements and the 45uA calc of current through the 51Ω
sense resistor, the V across the 51Ω ISense-12 resistor should be only 0.002V.
So a question is where is this 0.08V coming from? An unfulfilled -12V supply
for the E3 power pin might have been an explanation, as extra current might
be drawn out of the E3d.+in input due to the +in being pulled below
(negative to) the
E3 -power pin. But you say that pin is connected to GND, so the source of the
0.08V should be sought, some more comprehensive measurements around
the E3d inputs / ISenseR might help.
I thought I had answered where the Vcc and GND are connected on the comparator. Vcc is
connected to Vstart and GND to GND. ...