Re: Type 503 Oscilloscope Issues

Dave Casey

Evan -

Glad we've managed to at least get you back to where you started before the
scope died. To clarify, when you measure the +85V bus, you see the low
voltage of about 8,5V and V659 (you said V692, but I think you mean V659)
is dark. When you are not measuring this bus, is V659 still dark?

Dave Casey

On Thu, May 4, 2017 at 12:23 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:

Hello all,

So I just realized that I had two of the wires flipped from the diagram
that Dave had sent. I wired in sequential order, and did not realize that
my wiring to Pins 2 and 3 should be flipped. With that corrected, the trace
does appear, and the scope seems to be running normally (or at least as it
was before). However, running some sine waves through the scope, there
appears to be some distortion of the curves, with a warping of the image
towards the center of the display. This was present the last time the trace
had worked as well. The scope also seems to be running hot (although it may
have always done that).

I have pictures of the resistor readings and the wiring of the new 6.3 VAC
transformer here: Please disregard the tape
wrapping of the secondary wire going to the original Pin 6 wire. I only
made it white and orange to remind me that the wire is being elevated to
-3000 V (same color as the scope's HV wires).

From John, I had overlaid the schematic you sent with the resistor
readings from before. I do have the earlier model of the scope, as from
previously noting that I only have two tubes on the 12.6 V circuit (V334
and V434, both 6DJ8's). My serial number is 004418 if that helps (never did
post it before). From the Tektronix Service Scope issues I have from 1962,
I know that this model does not have some of the fixes that those >7000 had
gotten from the factory, but they were nothing that should prevent it from
powering correctly.

As for R659, it gave the same reading as before, at ~77.6 kOhm. The only
resistor that seems to have taken a beating from the arc was R626 (slight
black scorch mark on the top), but it still reads at 40.1 kOhm.

Since the transformer is now wired in correctly, and the resistors do not
seem to be damaged from yesterday's event, I re-did the voltage
measurements (being sure not to short anything this time).

I tried to adjust the -100 V bus via R641, but the largest value I could
get the voltage to was still just -85 V. The voltage using the original
R641 setting gave -80 V when the transformer was correctly wired, so it
does influence the voltage.

With the -100 V bus adjusted, I measured the other buses (although I know
they will be skewed because the -100 V is still not correct).
+250V measured at 305 V
+100V measured at 110 V
+12.6V measured at ~18 V
+500V measured at 470 V
+85 gave the same issue as before (~8.5 V, and no V692 turning on).

As Dave inquired, I am not actually using the analog voltmeter for these
readings. I am currently using my only "good" DMM (the one I used to
calibrate the analog meter), due to misplacing one of the analog meter's
probes. Since it uses non-jacketed banana leads, I am not able to use the
probes from any of my other meters, so I just have to base everything on
the DMM for right now.

- Evan

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