Lubrication; Semiconductor Checks - Tektronix 2235A Instruction Manual

Maintenance
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2235A
Instruction
To prevent damage from electrical arcing,
ensure that circuit boards and components are
dry before applying power to the instrument.
CLEANING. To clean the interior, blow off dust with dry,
low-pressure air (approximately 9 psi). Remove any
remaining dust with a soft brush or a cloth dampened
with a solution of mild detergent and water. A cotton-
tipped applicator is useful for cleaning in narrow spaces
and on circuit boards. If these methods do not remove all
the dust or dirt, the instrument may be spray washed
using a solution of 5% mild detergent and 95% water as
follows:
1. Gain access to the parts to be cleaned by removing
easily accessible shields and panels (see Removal
and Replacement Instructions).
2. Spray wash dirty parts with the detergent-and-water
solution; then use clean water to thoroughly rinse
them.
3. Dry all parts with low-pressure air.
SWITCH CONTACTS. The VOLTSIDIV and SECIDIV
switches are mounted on circuit boards within the instru-
ment. Care must be exercised to preserve the high-
frequency characteristics of these switches. Switch
maintenance is seldom necessary, but if required, use
this procedure.
. .
1. The VOI-TSIDIV switches contain cam-actuated
switches.
Most spray-type circuit coolants contain Freon
12 as a propellant. Because many Freons
adversely affect switch contacts, do not use
spray-type coolants on the switches or
attenuators.
The only recommended circuit coolants for the
VOLTIDIV attenuators are dry ice (CO, ) andiso-
propyl alcohol.
a. Use only isopropyl alcohol as a cleaning agent
for switches, especially in the area of the Verti-
cal Attenuator circuit board. Carbon based
solvents will damage the board material.
b. Apply the alcohol with a small, camel-hair
brush. Do not use cotton-tipped applicators,
since the cotton tends to snag and possibly
damage the switch contacts.
2. The SECIDIV switch is comprised of rotary-
activated contacts.
Use only deionized or distilled water at about
55°C (131°F) to clean the SECIDIV timing
switch. Tap water contains impurities that
remain as residual deposits after evaporation.
a. Spray hot water into the slots at the top of each
switch housing while rotating the switch control
knob. Use an atomizing spray device, and spray for
only about five seconds.
b. Dry the switch and circuit board on which it is
mounted with dry, low-pressure air.
c. Bake the switch and circuit board in an oven or
drying compartment using dry circulating air at
about 75OC (167°F) for 15 minutes to eliminate all
moisture.
d. Spray a very small amount (only about a 112 second
squirt) of a recommended lubricant, such as No
Noise, into the slots at the top of the switch housing.
e. Rotate the switch control knob about 180' and again
spray avery small amount of lubricant into each slot.
LUBRICATION
Most of the potentiometers used in this instrument are
permanently sealed and generally do not require
periodic lubrication. All switches, both rotary- and
lever-type, are installed with proper lubrication applied
where necessary and will rarely require any additional
lubrication. A regular periodic lubrication program for the
instrument is not recommended.
SEMICONDUCTOR CHECKS
Periodic checks of the transistors and other semi-
conductors in the oscilloscope are not recommended.
The best check of semiconductor performance is actual
operation in the instrument.
Scans by
AR TEK MEDIA =>