[time-nuts] Tek 602, no trace

Steve Rooke sar10538 at gmail.com
Sat Nov 8 01:26:00 UTC 2008


2008/11/8 Magnus Danielson <magnus at rubidium.dyndns.org>:
> Richard Moore skrev:
>>
>> Magnus, a few thoughts that have most likely already occurred to you --
>> 1) HV supply failure -- I think it will be around 2 or 3kV if working.
>
> It's 3,9 kV. There is a test point, but I need to dig up a very old HV
> probe lying around somewhere in the junk. Finally I get some use for
> it... maybe

So do you mean that it should read 3.9kV or that you have tested it to
be that value?

>> 2) X or Y deflection amp has failed, moving the trace offscreen.
>
> The X deflection amp seems to work at least.

If you place a meter between the X plates you should see 0 or very low
volts with the X position control in the middle position.
What voltage do you get between one of the X plates and ground? Is
there a beam-finder button on the scope as this should brighen up the
beam and bring it onto the display if it is too far off. Sorry, I
don't know this scope.

>> 3) CRT heater dead.
>
> No, I have a very faint ligthening up on the screen which the horizontal
> control can move on or off screen. I need to shield the screen from
> light to see it. It's so out of focus that it hits the full screen.
> Could be an HV issue, but I am not sure at this moment.

Quite often there is a little window in the screen around the CRT
shield which should give you a good view of the glowing heater. Make
sure there is a good bright orange glow. Cheaper/early scopes used ac
directly to the heater winding so there was never a problem with the
heater voltage but to reduce the ripple effect of the ac voltage,
better scopes used dc so you would be wise to check the heater voltage
in that case and look for something like 6-7V if the heater looks a
bit dim.

If the anode voltage looks good, check out the voltages at the cathode
and the grid. As the design of analog scopes try to keep the X and Y
plates near earth potential, you should see a large negative voltage
on the cathode and grid. If the grid is more negative than the cathode
by about 20V or more the beam is likely to be cutoff. You should see
the voltage difference between the cathode to grid drop (with the grid
being more negative than the cathode) as you increase the brightness
control. I don't know what the cathode voltage would be in your case
but with an anode voltage around 4kV I would be expecting to see
something in the region of -1.5kV give or minus 500V.

>> Either 1 or 2 should be easy to detect. Having the manual will
>> certainly help with repair. 3, however, is really discouraging.
>
> Certainly. I have enought of large scopes at a friends place to be able
> to salvage tubes before being tossed. I even think he still has the
> spare tube NOS. :)

Assuming any replacement tube has a similar spec you would be OK to
substitute but really need to check computability.

Hope any of this helps, I don't know too much about the Teks but have
some experience with old HP and Gould scopes. If you want to discuss
more feel free to PM me.

73, Steve
--
Steve Rooke - ZL3TUV & G8KVD
Omnium finis imminet




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