On Thu, 03 Jan 2013 07:29:26 -0000, you wrote:
HElo All,
I have here my old telequipment D43 on the work bench wich I try to restore.
This is not a HP agilent device, but I've seen some posts here about the D43
The problem is I cannot get the lines on the screen. I can only get two dots who I can move up, down, left and right with the controls.
Then the vertical amplifiers and horizontal amplifiers, CRT and HV
power supply are likely OK.
If the two dots are above each other, then that's understandable. They
shouldn't be side by side.
when I switch the device off I get the lines for a short moment.
Then the sweep itself is good (sawtooth generator).
Sommetimes the device comes on with the lines and works untill I use one of the time base controls. Then the picture dissapears.
If the scope has an "auto" position, try it. It may or may not. This
kind of scope waits for a trigger and then generates a sweep sawtooth.
No trigger = no sweep. In the auto position, it generates triggers at
about 50/second to give you a baseline.
The sweep output sawtooth is also missing when I cannot get the lines.
That's what to expect.
I've almost completely disassembled the timebase circuit board and changed a lot of resistors who where of value.
I also tried changing the valves with other valves I had here, but I'm not shore they where all ok.
I have a circuit diagram but unfortunaly without scope images
Feed a signal into the vertical amplifier or the external trigger
input, sine wave is fine. Follow that signal back into the scope. You
should see it amplified, then compared against a reference. The
output of that comparator is likely a square wave to a pulse depending
on the trigger level (I'm making guesses here), that square wave will
most likely be differentiated, that is, converted into a very narrow
spike pulse that is the same location as the edge on the other pulse.
Look for only one edge to be big, the other small in amplitude. That
is then fed to the sawtooth generator.
I had a somewhat similar problem in a D75 (transistor version,
perhaps), a 10 pf capacitor was open, and not allowing the trigger
pulse to hit the sweep generator. It would sweep, but not trigger.
You need to check all the power supply voltages (the low voltage ones,
not the HV for the CRT, likely just fine). Check the voltages at the
tubes as well. A leaky capacitor could throw those voltages off
enough to keep the circuit from working.
You'll have to deduce what the circuit should do, although if you do a
web search, you might be able to find some of the old tektronix books
(for free) that talk about how the oscilloscopes work.
Harvey
Who can help? Thanks
