Re: Type 503 Oscilloscope Issues

Dave Casey

All of the resistances that you have cited as low or very low need to be
measured out of circuit to get an accurate reading. This type of resistor
tends to drift high, not low. You can get a sense of whether or not
anything is drastically wrong here by measuring voltages as marked in the
schematic. Because you do not have the correct supply voltages, you cannot
expect the same bias voltages as what's marked, however everything should
be proportionally correct within an order of magnitude (i.e. V634 pin 3
should be approximately 60% of whatever the +100V bus is measuring). You
can also check the resistors one at a time by desoldering one of the leads
from the terminal strip.

R632 is just barely out of tolerance, and you may replace it if you so

R692 does sound a bit high, but I believe you previously reported a
measurement for R692 (before you removed and replaced V692) that was within
reason. It's unlikely that R692 has suddenly gone high. Perhaps you're not
making good contact for your measurement, or you have a less than perfect
connection with your soldering job? Regardless, if V692 is glowing gently
and you get a trace on the CRT, I wouldn't worry too much about R692.

You should know where R641 is as you've adjusted it before with no effect,
have you not?

As I stated earlier, you should be able to measure R624, so if you are
unable to get a measurement there, you need to determine why.

Dave Casey

On Tue, May 2, 2017 at 1:22 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:

Thanks Dave for that correction on R692. I had mistyped the color code in
my resistor calculator, and it did not click in my mind that the units from
my multimeter did not match (just assumed it to be of the same magnitude).

As for matching the resistors to the manual's diagram, I updated the
figure with the corresponding part labels (again, can view at
JUFwEfmnyFAcYtp6A). They should all be labelled correctly, although some
wires are difficult to trace and the resistors could be mixed up.

To simplify things, I have each resistor listed below as well:
- R611 = 151.2 k (good)
- R612 = 140.5 k (good)
- R621 = 94.7 k (good)
- R623 = 4.65 k (good)
- R624 = ? (could not get a measurement)
- R626 = ? (could not locate)
- R628 = 508 ohm (good)
- R630 = 537 k (low)
- R631 = 752 k (very low)
- R632 = 116 ohm (high)
- R634 = 20.5 k (low)
- R635 = 22.3 k (very low)
- R637 = 400 k (low)
- R640 = ? (could not locate)
- R641 = ? (could not locate)
- R642 = ? (could not locate)
- R644 = 465 k (good)
- R646 = 15.3 k (good)
- R659 = 77.9 k (low)
- R692 = 8.9 ohm (very high)

- Evan

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