Thanx for all the reactions guys, it was an old germanium transistor Q184 in the unblanking circuit. Chuck did me the suggestion to look specific at that transistor and he was damn right.
I replaced it for a 2N3906 and also his brother on the A timebase Q373. They are silicium transistors but functions perfectly.
So in a few days, problem solved :-)
The only thing what?s left is the timing from the sweep rates, they are about 20% to long. All of them on both timebases, so if somebody knows...
grtz and thanx so far for all the help, Ren¨¦
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--- In TekScopes@..., David <davidwhess@...> wrote:
The unblanking signals from the A and B sweeps are combined in the
horizontal display switch (SW530 5R and 5F located on schematic 2). I
would start looking for a problem there. Does wiggling that switch
make any difference?
Since it is so easy, you may want to check for the presence of the A
and B gate outputs which are copies of the two separate unblanking
signals before the horizontal display switch.
On Mon, 08 Oct 2012 13:14:41 -0000, "tek_547" <R.Kelbling@...>
wrote:
You are dead right Albert about changing the sweep time/div with the VAR knob. It seems the retrace comes from the last section of the end of the trace and changes up and down while turning on the knob.
I also checked the +350V and it?s still correct after the repair of C730. It is +353V with about 5mV ripple, completely in specs just as the other voltages from the power supply. All of them have only a few millivolts of ripple and the voltages are comfortable in specs.
When I turned the scope on today only the B timebase have the "dot problem", the A time base functioning correct. Very weird!
Suggesting that the problem is in the unblanking circuit in wich part of the circuit the defective component can be?
Maybe a capacitor or a tube, ideas?
Grtz, Ren¨¦
--- In TekScopes@..., "aobp11" <aodiversen@> wrote:
Hi Rene,
If you slowly change the sweep time/div with the VAR knob then you will see the retrace jumping from lower to higher level and vice versa. You will see why when you adjust Horizontal Position such that you can see the end of the trace.
Albert
PS Fred: some people have to work tomorrow;=)
--- In TekScopes@..., "tek_547" <R.Kelbling@> wrote:
Hi Albert and Fred, people are really quick on this forum :-)
I put the scope on a few minutes ago and I have now two dots; one below and one above in the trace picture.
When it?s not trigering there are (ofcourse) no lines but only two dots. Also on Ext. gives the same two dots.
But the retrace line as Fred called it is in the lower part of the trace when the trigger is set to negative and at the upper part when trigering is set to positive.
It?s now already a bit late here in Holland so tommorrow I check the +350V line again.
Thanxxxx so far!
