Re: Tek 7603 Followed Me Home

bobh@joba.com
 

Chuck & Dave,

The fuses are good.  The jumper for 120/240 is there but not connected on one end.  I think this is correct since the three position plug seems to also parallel the windings for 120v.

I had tried a 7A22 & a 7B50 but the 7B50 is probably bad so I replaced it with a 7B53A and I now have some lights on the plug-ins and graticle light.  No trace, but moving the trigger knob does cause the trigger light to flicker as expected.

I can't work on it again until this evening.  I'll re-check the voltages and check the ripple(s) with another scope.

Bob.

On 9/9/2018 7:36 AM, Chuck Harris wrote:
No plugins, and the scope will do nothing.
The little green lights burn out all of the
time.

The manual tells you everything you need to
know about power supply diagnosis. It is
expecting that you will make DC measurements
with a DVM, and ripple measurements with another
scope, set to LINE trigger, and sweep at 5ms/div.

In this mode, ripple will be stationary.

The really high frequency glitches on the power
can be ignored, but the 60Hz and 120Hz ripple
are important, as are the general noise level.

The unregulated outputs are not critical as
to value, but do need to be close. They are
not especially critical as to ripple, expect
high values. Their purpose is to feed regulators.

They will vary greatly depending on your mains
voltage, and the mains setting of the scope.

The 7603 has a linear power supply. All of the
regulators are referenced to the -50V regulated
supply. You show it way off, everything else will
be off proportionately. Fix it first. Don't just
adjust it, fix it.

-Chuck Harris

Robert Hay wrote:
So far no plugins and the light isn't lit. I'll check it.

Bob.


On 9/8/2018 7:43 PM, Robert Hay wrote:
I have seen this Tek 7603 scope sitting on the table at the Tek Country store for
at least three years. I have tried to power it up and twist some knobs several
times over the years with no response. They have been asking $35 for it and I
noticed today there are about 5-6 price stickers stacked up under the current one.

I have been thinking a 7603 would fit into my ensemble if I clear space for it by
giving another scope to the Tek Museum. So, I asked if they would take $25 for it
and they did. So, here it sits with the covers off and the power supply hanging
out the back. It doesn't do nut-tin when powered up.

The main fuse, the fuse on the regulator board and the one on the power supply
board above the caps are good. I checked the power supply voltages on the regulator
board with the following results:

Volt VDC VAC
130 114 11
50 44 5
5 4.396 0.25
15 13.2 1.4
-15 -13.17 1.3
-50 -44 4.8

Unregulated Voltages

50 66 0.16
-50 -52 13
15 24 0.04
-15 -24 0.1
5 12.4 0.05

Seems to be discrepancies between the ripple on the corresponding regulated and
unregulated supplies which I don't understand.

The 130 volt supply is partly made up from the 50 volt supply and the voltage on
the emitter of Q850 should add about 40 volts but I measure 10.8 volts DC there.
Maybe I see it now, if the 50v supply is at 44 volts there is no way the emitter of
Q850 can get to 40 v.

I appreciate any ideas from folks especially those who have been thru a 7603
before. Haven't had a chance to research the archive but will do that before doing
more troubleshooting. I can't take another scope to the Tek Museum until I know we
can bring this one back to service.

Bob.







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