IBM 1620 Manual page 40

No----------------------I
Data Wrong
in MBR
1
1. False Check
Check VRC
Ckt.
yes----l
!
Refer to core storage
servic i ng procedure,
(See Page 4.3)
o
A lack of pattern is indic-
ative of a failure common
to the entire memory but
external of circuits such as:
1. Diode across R 102
defective.
2. Memory over temp therma I
or fan defective
(temp should be 100
0
±3)
3. Memory operating voltage
incorrect. The +12 and
+30 should have voltage
difference as indicated
on marginal supply when
measured at IIA" gate with
a 1/4% accurate meter
(Weston 90 1, PiN 460879
or equivalent).
4. Electrical noise (see General
Trouble-shooting Information
(See Page 2.3)
4.2
l---------------yes
At this point, run system and record
the following:
1. Address which failed
2 • Bit tha t fa i led
3. Was bit picked or dropped?
4. An
I/o
Op code pattern may
appear. If so, check write
check light. If on, see
I/o
Section I. If off, check gating
of MBR and MDR from translator.
After recording a series of failures,
study recorded information, looking
for an address or bit pattern.
1. Address pattern
a. A common digit in units tens,
hundreds, or thousands, above
or below 10 K.
b. Groups (banks) of addresses
which contain this pattern.
2. Bit pattern
a. A particular bit or group of
bits failing in any address.
b. Is failure always above or
below 50?