Hi Jose,
On another hand, I have checked the 1A1 plug-in CH1 SIGNAL OUT and
there I
get also a distorted signal, similar to what I get in the 545B but
without
the 'trace back'
Power supply ripple is an uncommon fault in my experience of the
530/540/550 series.
It sounds like the 1A1 may be the cause of the problem. There were 2
broad versions of the 1A1, the early ones with nuvistor inputs and
the later ones ( or modified early ones) with FET inputs. You can
tell which type you have by looking at the input modules on the sides
just ahead of the input attenuator. It there is a little PCB with
FETs then it's a late model, if it has a blue casing with a screw in
the middle, that's the nuvistor shield (2 tubes per channel). Very
early ones have exposed nuvistors with no shield. It may be a faulty
tube or dirty connections.
An ideal test would be to find almost any other 1- or letter- series
plugin as a substitute.
Somebody commented about the power supply temporized startup. It is
clear
that there is a vacuum relay(?) which in turn activates a large
multi-pole
relay.
That's a thermal relay running fron the 6.3 volt line. It activates a
larger multi pole relay which applies B+ once the heaters are warm. I
have had them fail with burnt out heaters. They are getting expensive
and I have made up a little solid state substitute (cct available if
you want). 30 seconds is about right.
And, to my surprise, it seems to be the power switch!. It smells to
burnt bakelite... Is this a common fault?. Could the switch be
repaired?.
It's a simple toggle switch - easy to replace with a generic part.
Could you comment about the usual starting up sequence?. I
have also found that the neon bulbs in the circuit have a curious
startup:
first, all of them light. Then they start to put off gradually (not
all
same time). And then, when the power relay clicks, some of them
light
again. Is this usual?.
This is completely normal. Many of those bulbs are there to limit
tube electrode voltages, and some are coupling devices. Not all the
B+ is switched by the startup relay so there are some out-of
tolerance voltages present during warmup up which have to be limited.
You will find some of the neons in the timebase filcker in sync with
the sweep - visible at slow speeds.
is any way to check the scope (at least part of it) WITHOUT the 1A1
plugin,
I would love to hear about that, as I have no other plug-in and I
think
perhaps the plugin is faulty. What should be shown on the scope
without the
plug-in?
I'm not sure whether you can run the 545B without a plugin. The 547
has a plunger switch that is activated by the plugin and if there is
one in your scope (a plastic plunger at the top of the rear panel of
the plugin compartment) then you can operate it without the plugin.
Otherwise the power supplies are not loaded properly. There are a
couple of tubes in the timebase whose heaters are in series, supplied
from the +100 volt supply and drained by a load in the plugin. If
there is no drain, the tubes won't heat and the timebase won't work.
Also some vertical amp designs need +67 volts applied to their inputs
which is normally supplied by the plugin. I'm not sure whether the
545B is one of those.
I hope this helps Jose. You have got me onto one of my favourite
subjects!!
73
Morris Odell
