Service Manuals, User Guides, Schematic Diagrams or docs for : HP Publikacje HP-Bench-Briefs-1977-03-04
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T-PACKAn3
F
MARCH-APRIL 1977
E 1 USE
N
instrument Po uae s
twdbits. *
Ttw HP 50WA Signamre Analyzer is a But in the programmed digital world, ser-
ian's tool for field troubleshootiryl vice sCtrema&s are devoid of waveform
ocess0r-W intehrmts-down voltage and other service E for
the not very comforting all
bit strearm look pretty much alike 0rr an
oscill . The pro\lrdem is com
analysis. It has been learned that although with microprocessors,
the microprocessor has simplified instru- controtlers. for a m
ment design, it has complicated trouble- with them there is n
without the use of specid extender
nd. However, when association between
particular sections
example, if a k
fumtion fails in an
product, a service manual might
n& r d circuits that m-
checking the i t g&
trbt that function. With microprocessors,
on the other hand, key debouncing is cost actually fell and th
stream is faulty the technician can trace it more likely a timeshared function, tying time amounted to appr
baek through gates and memory elements up the whole processor for a brief the overall development
until he isolates an element with correct moment. When it fails, any one of a large goal of wrviceabidity
number-of IC's could be faulty. now has about 40
The signature analyzer is a troubleshoot-
ing tool desigrred qmciP&ly for micro-
processor-based- products. More inetru- IN THIS ISSUE
ments that are rn'wopracesor based will
be inboduced this year than the sum of SIGNATURE ANALYSIS
us85 an annotsad all computer systems installed to date.
re 2 for an example) Microprocessors are relatively low in cost
SERVICE TRAINING
*
voltages and wave- and easy to design around. But, they are
just as complex and diffkuk to repair as SEMINARS
computers because of time-reja
Industry predicts that ten m 3476AB PRODUCT
will fail in the field this year, IMPROVEMENT
them in microprocessor produ
int at which circuit opera- will cost one to two billion SAFETY SERVICE NOTES
from there t r a d s repairs. Thus, the signature analyzer
failed comwnent promises to have a significant i OR NEW SER VICE NOTES
in m n t wviwems.
WWW. HPARCHIVE.COM
s
DESIGNING IN SIGNATURE
ANALYSIS
a
A portion. of the circuits read-only-
memory - perhaps 5% - must contain a
special program for stimulating the
various nodes in the circuits. The stimula-
tion serves more to excite or force a state
change on the nodes, than to generate
meaningful data. Frequently this stimulus
program may be merged with the
products performaneverification pro-
gram. The correct signatures are
developed by simply exercising the
THE OPERATING AND SERVICE picture shows only the signatures related various parts of a circuit that i s known to
MANUAL to the particular test directing the be good and noting the results on the
technician's effort toward the important circuit diagram.
Besides the design engineer, the writer of areas on the board. The ROM prugram
the service manual made an important even simulates interrupt signals, ensuring
contribution to the successful application however, that they occur predictably at
A second requirement is to break feed-
of the signature analysis to the 3455A the same spot within a window so that
back paths within the circuit, either by
Voltmeter. The service manual is written stable signatures result.
using hardware switches, jumpers or
in such a way that a technician, un- connectors, or by disabling gates with
familiar with the signature analyzer can The siwature analyzer h s its own self
a
software. This requirement is necessary to
walk up to a defective voltmeter, read the check. Each test set up is tested by
touching the power supply voltage with prevent a fault from being fed back
instructions and within a short time
locate the fault. One element in the
manual is a troubleshooting flow chart
(see Figure 3) that systematically guides
the technician through the fault finding
the instrument's probe to input a
sequence of all one's. If this characteristic
signature is correct the setup conditions
and framing of the measurement window
around and disturbing all data nod?.
When these two requirements are met,
back tracing a fault to its source is a
straight forward process of tracing faulty
a
are verified. Specifically, this tells the signatures.
process.
user that the switches on the signature
The initial tests may or may not rely on analyzer, as vel1 as all the jumpers,
signature analysis. They allow isolation of switches and control buttons in front and
In using signature analysis t h e procedure
the fault down to a specific area. Diap rear of the voltmeter are correctly s e t
varies slightly, depending on whether the
nostic programs cannot carry on from This means the confidence level of the
fault lies in the kernel (the minimum con-
here, since they do not have access to user is very high at the start of a test.
figuration of microprocessor and ROM
individual nodes, but it is from here on necessary to run the simplest test pro-
down to the components t h a t signature WHAT'S A SIGNATURE? gam) or in the outlying circuitry.
analysis excels.
Everything depends on the signature. A
At t h i s level the repair man uses the kind of compressed "fingerprint" of the
annotated schematics and graphs of board data present on a node, it is compared If the fault is in the outlying circuitry (a
layouts together with the flow chart, to with the correct signature printed on the keyboard or display scanner, input/
find the bad node. A node is defined as a schematic of the product s that any
o output latch, etc.) the technician simply
terminal of any branch of a network, or a discrepancy may be noted and traced to switches the circuit to the diagnostic
terminal common to two or more the source. The signature is derived mode. Then, guided by the manual, he
branches. Also called junction point, through linear-fedback shift registers. uses the test instrument to trace faults
vertex or nodal point. In some cases the which generate pseudo-random binary back to their source. But what if the
manual indudes instructions as to which sequences. For signature analysis, bit problem lies in the kernel, and even the
I to replace. In other cases the use of a
C sequences being measured are summed in ROM stimulus program will not run?
logic probe, which is an integral part of modulo 2 with the register feedback. The Here, the microprocessor itself can pro-
the logic tracer may be required. A register is clocked by the same clock as vide a stimulus if its address counter is
current sensor, such as the HP 547A, the bit stream under measurement. Input allowed to sequence through the address
helps to find short circuits between traces sequences may be any length, but a t the field. To do t h i s it is only necessary to
or to ground and is particularly helpful end of the measurement, only the residue open the datarfnstruction bus and force
when bus problems are encountered. remaining in the register is looked a t the no-operation instruction onto it. This
These 16 bits, when displayed in a 4 digit stimulus program checks out all the
The 3455A Service Manual shows format, comprise the signature of the address lines and the individually enabled
pictures of the board and defines the set m u r e d bit stream. Figure 4 shows a ROMs as well. All of these nodes are
up for each test (see Figure 3). Each simplified block diagram of this concept. readily characterized with signatures.
WWW.HPARCHIVE.COM
-
SIGNATURE ANALYSIS
.Since signature analysis relies on the synchronous or disabled condition when accounted for in the new products utiliz-
ability of an instrument to control itself that is required for a particular test. ing signature analysis. However, in the
in a synchronous manner, asynchronous long run, these coots will be more than
circuits, like monostables djrect-memwy- offset by the serviceability of the instru-
access, dynamic memory, or interrupts, In summary, HP expects the Signature ment. And, as of today Signature
need to be carefully controlled. Analyzer to have a significant impact on Analysis i s the first new and workable
Generally, simple provisions in the hard- our own in-house service costs. True, concept for servicing microprocessor
ware can be made to force them into a there are some design costs to be based instruments.
BUFFER
VAL10
MEMORY
ADDRESS
FIGURE 1 Exampb of Block Di.anrn with Sfpatufa
.
PARCH IVE.CO M
I., :I
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