Hi James,
This is your project so it should run on your time, no problem continuing later. My comments are below for next time you are on the scope:
On the primary AC side of CR1721, from the transformer centre point across the
coils, one of the the readings measures 64 volts, whilst the other measures
130v
This says what you think as center point is actually one of the ends. Point
marked as [9] is center tap and should go to mid point of C1722/C1723. Two
ends are [7] and [3]. Measurements should be [9] vs [3] and [9] vs [7].
These were exactly the points which were measured across
Perhaps the wires are mislabeled. Your 24VAC test will tell us what is happening.
I do have a 24v transformer but that shall have to wait until tomorrow now as
it's late here.
Good idea to rest before attacking it again.
All of the bridge rectifiers had been disconnected apart from CR1721. All
this issue with the high voltages made me wonder if the other rails needed to
be connected, so they were connected up again.
Unlike an SMPS, linear supplies do not need a minimum load on the transformer. It is OK to disconnect some supplies while debugging as long as they don't depend on each other (like +15V needing +65V).
Can't see anything obvious, but this time when I disconnect the rails, they
are staying off until the 65 and 140 volt problem is indentified and resolved.
Agreed.
You mentioned there is a regulator connected in the dim-bulb setup. What kind of regulator is it, and is it still connected when bulb is not there? Is there any possibility regulator is stepping up the voltage? It is best to connect the primary directly to 24VAC and, when things are fixed, to 120V.
With 120VAC at primary we expect about 58VAC from center tap to each side.
With 24VAC at the primary we expect 58VAC*(24/120)=11.6VAC from center tap to each side ([9]-[7] and [9]-[3]).
As an additional check [4]-[4] secondary should be ~ (22.5V/sqrt(2))*(24/120)=3.18VAC with 24VAC input.
Ozan
