IBM 3277 Troubleshooting Manual page 28

Display station models 1 and 2
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I
The Troubleshooting Diagrams (29 sheets) in this section
should
be
used as directed by the Symptom I ndex (Section
3). The diagrams are flowcharts arranged in a sequence that
ensures successful trouble resolution in a minimum time.
The steps in the flowcharts must be followed in sequence
because successive steps depend on the actions and resu Its
obtained in preceding steps. Although the sequence may
seem illogical and shortcuts may seem apparent, deviation is
discouraged to avoid unnecessary duplication of effort and
prolonged service calls.
Sheet 1 determines whether the symptom experienced is
caused by a display station problem or by a control unit
problem. Subsequent flowcharts cover display, keyboard,
selector pen, and card reader malfunctions. Additional
sheets analyze power troubles and miscellaneous keyboard
assembly electrical and mechanical troubles.
Observe good safety habits while working on the display
station with power on. High voltage is present at the CRT
anode, the yoke assembly, the HV power supply, and the
voltage distribution points. Always remove power from the
display station when removing or replacing logic cards. This
avoids damaging circuitry on that card or other cards
feeding it.
The flowcharts use the terms "replace card XX" and
"change card XX". "Replace" means to reinstall the same
card that was earl ier removed; "change" means to install a
new card from stock. The old card being changed is the
probable cause of the failure.
Two unique symbols are used in the flowcharts. The
symbol
means to probe (with the logic probe) the point designated
in the symbol. Seven logic probe conditions can
be
seen
with the older style probe (PN 453652). An output line
from the probe symbol specifies one of the seven con-
ditions. If the observed condition is the same as that
specified in the flowchart, continue down that part of the
flowchart. If the observed result is different from the
specified result, use the part of the flowchart labeled
"Other". The seven logic probe observations specified in
the flowcharts and their definitions are as follows:
1. Red - solid red.
2. Green - solid green.
3. Red Blink - solid green with one (and only one) red
blink.
Section 4. Troubleshooting Diagrams
4. Green Blink - solid red with one (and only one) green
blink.
5. Pulsing Red - solid green with regular red pulses. (Any
frequency of pulses as long as green indicator appears to
stay on.)
6. Pulsing Green - solid red with regular green pulses. (Any
frequency of pulses as long as red indicator appears to
stay on.)
7. Red and Green - approximately equal red and green
pulses (any frequency).
The same conditions can be observed using the new G LP
(General Logic Probe), PN 453212. The difference from the
older-style logic probe is that the G LP uses UP in place of
red
to indicate a plus level and DOWN in place of green to
indicate a minus level. This difference must be kept in mind
when troubleshooting with the GLP because the flowcharts
in this manual were designed for use with the
ol~r-style
logic probe.
' ,
The card-shaped symbol
appearing at the end of a diagnostic sequence gives the
location of the card(s) to be replaced that will repair the
problem. It also means to take the following action:
1. Turn power off.
2. Change card
(5).
3. Turn power on.
4. Verify that trouble is repaired.
5. Replace covers.
6. Return display station to user.
When more than one card is listed in the symbol, isolate
the failing card by card-swapping from among those
specified. Change the failing card, and return the others to
stock. If changing the specified cards does not repair the
problem, check
all
voltages on the A 1 board backpanel at
these card locations. Use Diagram 6-14 to identify the
voltages and voltage pins.
The flowcharts call out certain check, adjustment, and
removal procedures. Because of their length and their
utility as standalone procedures, they are contained in
Section 5. Flowchart references to these procedures appear
as three- or four-digit numbers, indicating the paragraphs In
Section 5 where the procedures are found.
Troubleshooting Diagrams
4-1

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