Service Hints - IBM 1620 Manual

SERVICE HINTS
Card Reader Punch
Trouble-shooting Methods
Removing the error relay driver A2C07 effectively
cripples the error stop circuits.
Grounding either the read buffer ready latch or the
punch buffer ready latch permits continual transfer of
data between the buffer and the 1620, while the 1622.
is stopped. This permits scoping the data transfer cir-
cuits without cards in the 1622.
Reader Scan Ring - RSR
Reader scan ring trouble wi II usually show up as dropped
or extra bits in the SCR. To check:
1) Turn on the read row bit scan latch by grounding
A2ClO F (04.10.08.1). The RSR should now be
running.
2) Scope timings and levels using marginal voltages
as needed.
Row Bit (RB-2)
If the RB-2 read sense amplifier is failing, the SCR
will contain all "C" bits after reading in a card
containing miscellaneous punches.
If
a single position of RB-2 fails when displayed in the
SCR, the SCR will contain "C
II
bits regardless of data
in the associated card column. Also, a read check
will occur (B2 light on) for any column containing as
odd numbers of holes. To check:
1) Run a test deck with ripple pattern if it appears
that there is no output from the RB-2 sense amp-
I ifier.
2) If it is a single column failure, run a test deck with
a punch in the failing column.
3) Scope sense amplifier output at A 1 B05 AF
(04.30.02.1) using internal sync.
a. If there is no output using the ripple deck,
the trouble could be the common brush,
common brush transi.stor, display switch
contacts, CLC and CLC relay points, or the
sense ampl ifier.
b. If there is no output for a single position, the
trouble could be the individual reading brush
and circuit, read brush resistor, or connector.
c. Incorrect CB timing will give reading failures.
Note: The same testing procedure is used for RB-2
punch sense amplifier. Items a. and b. apply to the
punch side also. Scope at A1 B04 AF (04.30.02.1).
3.22
Row Bit Register 2 (RBR-2)
This single latch is turned on by the output of either
the read or punch RB-2 sense ampl ifier. To check:
1) Run same test decks as when checking RB-2.
2) Scope RBR-2 (on side) output at AlB 18 B
(04.25.03.1).
Single Character Register (SCR)
Failures of the RSR, inhibit drivers, SCR latches,
RB-2 and RBR-2 will show up in the SCR. If a check
of the RSR, RB-2 and RBR-2 shows that they are
functioning properly, a further check of the SCR and
associated circuits is indicated.
SCR failure indications:
1)
Groups of ten dropped (SCR blank), for example:
o
through 9, 10 through 19, 20 through 29, etc.,
indicates a failure in the selection (decode)
switches in the tens part of UTR.
2) Pattern in groups of eight (SCR blank), for example:
1, 11, 21, 31, • • • • • 71 or 4, 14, 24, 34,
44, • • • • • 74, indicates a failure of a
selection (decode) switch in the units part of U TR.
To check:
a. Turn on RBR-2 latch by grounding AlB 18 P
(04 .25 .03. 1).
b. Turn on the read select key and single cycle
to the fai I ing position.
c. Turn on the not units advance key to prevent
UTR from stepping.
d. Depress the start key.
The failing position should be reading and writing in
the read buffer. Scope read and write decode switches,
A1 D05 F and H (04.30.06.1). The voltage probe can
be used to determine that a decode switch is selected.
However, the current probe must be used to check that
the decode switch and current source circuit is func-
tioning properly.
3) Pattern of all 1 bits or all 4 bits, etc., dropped,
indicates a possible failure of an inhibit driver or
one of the SCR latches. To check:
a. Read in one card which contains punches
associated with the failing bit.
b. Turn on read select switch.
c. Depress CE start key. The clock and UTR
should now be running and circulating the
character through the 80 positions of the read
buffer and associated circuitry.
d • Sync on BO.
e. Check levels and timings of the sense ampl ifier
strobe, sense amplifier output, read/write
current or voltage, inhibit lines, and SCR
latches.
f. Vary marginal voltage as needed .•