Tektronix 585 - Page 48

Maintenance — Type 585
Visual Inspection
You should visually inspect the entire oscilloscope every
few months for possible circuit defects. These defects may
include such things as loose or broken connections, damaged
binding posts, improperly seated tubes, scorched wires or
resistors, missing tube shields, or broken terminal strips. For
most visual troubles the remedy is apparent; however par 
ticular care must be taken when heat-damaged components
are detected. Overheating of parts is often the result of
other, less apparent, defects in the circuit. It is essential that
you determine the cause of overheating before replacing
heat-damaged parts in order to prevent further damage.
Soldering and Ceramic Strips
Many of the components in your Tektronix instrument are
mounted on ceramic terminal strips. The notches in these
strips are lined with a silver alloy. Repeated use of excessive
heat, or use of ordinary tin-lead solder will break down the
silver-to-ceramic bond. One application of tin-lead solder
will not break the bond if excessive heat is not applied.
If you are responsible for the maintenance of a large
number of Tektronix instruments, or if you contemplate fre 
quent parts changes, we recommend that you keep on hand
a stock of solder containing about 3% silver. This type
of solder is used frequently in printed circuitry and should
be readily available from radio-supply houses. If you prefer,
you can order the solder directly from Tektronix in one
pound rolls. Order by Tektronix part number 251-514.
Because of the shape of the terminals on the ceramic strips
it is advisable to use a wedge-shaped tip on your soldering
iron when you are installing or removing parts from the
strips. Fig. 5-2 will show you the correct shape for the tip
of the soldering iron. Be sure to file smooth all surfaces
of the iron tip to be tinned. This prevents solder from build 
ing up on rough spots where it will quickly oxidize.
When removing or replacing components mounted on the
ceramic strips you will find that satisfactory results are
obtained if you proceed in the manner outlined below.
diss
Fig. 5-2. Soldering iron tip properly shaped and tinned.
Fig. 5-3. Correct method of applying heat in soldering to a ceramic
strip.
1. Use a soldering iron with a 50 to 75-watt rating.
2. Prepare the tip of the iron as shown in Fig. 5-2.
3. Tin only the first '/ I6 to ’ / 8 inch of the tip. For soldering
to ceramic terminal strips tin the iron with solder containing
about 3% silver.
4. Apply one corner of the tip to the notch where you
wish to solder (see Fig. 5-3).
5. Apply only enough heat to make the solder flow
freely.
6. Do not attempt to completely fill the notch on the
strip with solder; instead, apply only enough solder to cover
the wires adequately, and to form a slight fillet on the wire
as shown in Fig. 5-4.
Fig. 5-4. A slight fillet of solder is formed around the wire when
heat is applied correctly.
In soldering to metal terminals (for example, pins on a
tube socket) apply the iron to the part to be soldered as
shown in Fig. 5-5. Use only enough heat to allow the solder
to flow freely along the wire so that a slight fillet will be
formed.
5-2