HP 3457A Service Manual page 162

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3457A Replaceable Parts
Table 6-5. List of Part Changes
Operational Amplifier A2U516, part no. 1826-0635 (OP-07CP), has been replaced with part
no. 1826-1382 to achieve better initial time drift of VOS to guarantee 90 day/l year
specifications, Ferrite Slab A2US02A (part no. 1200-1207) has been added to eliminate RFI
generated by A2U502. Inductor A2L501, part no. 9100-1788, has been replaced by a jumper
wire (A2JM503)
to reduce
power supply noise generated
by Processor A2ZUSOl. These im-
provements have been implemented on A2 Assemblies which have an ERC (Engineering
Revision Code) of 2521 or greater.
Operational Amplifiers A2U211 and A2U212, part no. 1826-1133 (LMIICH) have been
replaced, in all applications, with part no. 1826-1381 to reduce noise and improve offset
drift. The new part will be found on A2 Assemblies which have an ERC of 2524 or greater.
Resistor A2R122, part no. 0757-0410 (3019) has been replaced, in all applications, with part
.no 0757-0284 (1500) to eliminate a parasitic oscillation which causes an excessive input cur-
rent in A2U101. The new part will be found on A2 Assemblies which have an ERC of 2529
or greater.
Resistor A2R219, part no. 0757-0442 (10KQ) has been added to provide extra operating mar-
gin for A2U214, This part will be found on A2 Assemblies which have an ERC of 2551 or
greater. Printed circuit board becomes Revision B.
Relay A2K106, part no. 5180-8233 has been replaced, in all applications, with part no.
0490-1556. This change was made to standardize part useage with a higher quality part.
Relays AIK851 through AIK860, part no. 0490-1461, have been replaced, in all applications,
with part no, 0490-1576 to standardize relay usage and reduce cost. These parts will be found
on HP 44492 PC Assemblies which have an ERC of 2644 or greater.
Capacitors A2C532 and A2C533, part no. 0160-2343 (100pf) have been added to A2
Assemblies to reduce the common mode signal present at A2J501. These parts will be found
on A2 Assemblies which have an ERC of 2703 or greater. Printed circuit board becomes
Revision C.
The Al Main Controller Assembly (part no. 03457-66501) has been replaced with the All
Main Controller Assembly (part no. 03457-66511). This change was made to add Option 700
(CHIL language). The All assembly is a direct replacement for the Al assembly.
Resistor A2R505, part no. 0757-0465 (100Kq) has been replaced. in all applications, with part
no. 0757-0472 (200Kq) to insure that the microprocessor (A2US01) always starts with a reset
signal at turn-on, The new part will be found on A2 Assemblies with an ERC of 2708 and
greater.
EPROM A1U502 (part no. 03457-88804) has been replaced, in all applications, by part no.
03457-88805 to correct a timing error of the "voltmeter complete" signal when using the
4-Wire Ohms function and to eliminate the possibilty of shorting two input channels when a
"device clear" signal is received while the instrument is executing a scan list.
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