12 Oct
2025
12 Oct
'25
10:28 p.m.
I got a few different replies, so I will try to answer them all in one go.
I too could not understand how 5V pulse could possibly be at a steady
voltage given the input. But today I found a capacitor on the physical board
that is missing from Tony's schematic. I haven't yet worked out how it is
connected but I am trying to re-draw the schematic in KiCad so I can add
corrections. I am not sure I have the patience to completely re-draw the
whole thing but I will try to get at least this area correct.
I measured AC OK by adding a pull up resistor, but if I am honest, I forgot
about this in my latest measurements. I have also looked at Power OK,
knowing that AC OK needs a pull up resistor, and it is logically false, so
it is definitely saying the power is not OK. However, I am thinking that I
shouldn't be too concerned about the AC OK signal because it is clear that
the 5V output is out of spec being at around 4.3V, so I think I probably
need to fix the 5V output and then perhaps the AC OK will sort itself out,
or at least I can fix AC OK once the outputs are actually valid. As far as I
can tell the Power OK and AC OK signals don't influence the operation of the
PSU.
Given that I do get an output of 4.3V, I would have thought that the
thyristor was not being switched on.
I have measured Raw 5V and it too is around the same voltage as the 5V
output. In fact both now measure about 4.4V. I checked the resistance
between the junction of the +5V rectifiers and the +5V output and it is
about 0.1R, so I don't think there is a break in continuity.
I hadn't spotted the capacitor on the 12V Pulse output. The rectifier output
for 12V looks like this:
https://rjarratt.wordpress.com/wp-content/uploads/2025/10/h7842-12v-secondar
y-side-rectifier-output.png and 12V Pulse looks like this:
https://rjarratt.wordpress.com/wp-content/uploads/2025/10/h7842-12v-pulse.pn
g.
Vstart is 11.3V and Vz is 6.4V. I have not been able to find where Vz comes
from on the schematic either, if I elaborate the KiCad schematics further I
will try to find its source. The supply to E1, E2 and E3 is 11.3V,
referenced to the GND output, the GND pin on E1 is -12.9V and the GND pins
on E2 and E3 are -0.7V
Let me know if I have missed anything.
Thanks
Rob