Re: Type 503 Oscilloscope Issues

Dave Casey

We can use the voltages​ you've measured across the resistors and the
design values to get a general idea of the currents, so don't worry about
unsoldering them all.

Dave Casey

On May 5, 2017 9:07 PM, "enchanter464@... [TekScopes]" <
TekScopes@...> wrote:

So I re-did the voltages with a new DMM, and I found out that the issue
previously was with the leads. The clips from the older meter were not
shielded/jacketed and caused some shorting between wires that were nearby
to the area it was attached (for the 85V bus). With the new meter and
leads, the voltage measurements for the buses and resistor points are

Bus voltages:
-100V bus = -86.1 V
+250V bus = 308 V
+100V bus = 122.6 V initially, but decreased to around 115 V

+12.6V bus = 14.6 V
+500V bus = 492 V

+85V bus = 90.2 V

Resistor voltages (In order: 1. left of resistor to ground, 2. right of
resistor to ground, and 3. voltage with leads across resistor)
R640 -> 10.6 V, 90.7 V, 74.2 V

R641 -> 10.2 V, 1.7 V, 9.2 V
R642 -> -87.1 V, 1.7 V, 78.6 V
R644 -> -0.3 V, 1.3 V, 1.7 V
R659 -> 308 V, 90.8 V, 214 V

I still have not found the missing lead for the old analog volt meter, so
I ended up ordering a replacement set. Once that comes in, I can re-check
the values again with that meter.

Also, I know some have mentioned measuring the current across the
resistors, but is there a way to do this without desoldering them (to break
the circuit and insert the meter)? I don't mind desoldering them, but I
know there were concerns about doing so and the damage it could cause.

- Evan

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