HP 5890 SERIES II Service Manual page 18

PART D FUNCTIONAL SYMPTOMS
This section contains symptoms (other than those that appear on the visual display) that indicate a pos-
sible problem. Typically, these types of symptoms can be associated with a specific functional area of
the instrument.
Zone doesn' t heat all other zones O.K.
With an Ohm meter measure the resistance of the cartridge heater (should be about 200- 220 ohms).
With the power removed this can be measured by removing the J9 connector for INJA, INJB, DETA,
and DETB. To measure the AUX zone remove the J14 connector. The pins are labeled on the main
board next to the appropriate J connector. Replace the cartridge heater if it is open or shorted. If the
cartridge heater tests O.K. and sensor test O.K. (see temperature sensor resistance chart), the problem
is in the zone control on the main board and the main board should be replaced. To measure resis-
tance of sensors remove connector P7, sensors are labeled on main PCB.
Zone temperature is unstable.
If Zone will not reach desired temperature or cycles over more then plus or minus 1 degree C then the
insulation around the zone and the insulation of the oven shell should be examined and additional insu-
lation added if necessary. Also refer to the operating manual to verify the zone is being used proper-
ly(i.e., oven at - 50 degrees C, injection port at 100 degrees C). This type of operation will not work.
The Main Board is generally serviced from a replacement aspect, the introduction includes an illustra-
tion of its functional configuration followed by information about its connectors and test points.
Any replacement or space electrical parts that are subject to damage by static electricity will be shipped
in static- protective bags or containers. Be certain to utilize these protective devices when storing items
of this nature.
Generally, since board or module replacement constitutes the majority of electronic repairs, the only
electronic test equipment necessary is a quality Volt Ohm Ampmeter.
The HP 5890 Series II GC contains a minimum of four and a maximum of nine electronic boards. The
four boards always installed are one of the AC Power Boards, the Keyboard and Display Board(usually
done as one module), and the Main Board. The actual AC Power Board located in the rear of the instru-
ment behind the column oven compartment is one of three possible boards based on the voltage and
phase configuration of the line. The Keyboard and Display Board are two boards located on the front of
the Electronics Module. The Keyboard plugs directly into the Display Board. The Main Board is
mounted inside the right side panel of the instrument and occupies most of the space in the Electronics
Module. More importantly, the Main Board contains most of the instrument' s electronics.
General Description:
The 05890- 60015 PC board is a collection of circuits which allow operation of the 5890 Series II gas
chromatograph. The circuits on the new board include power supplies, CPU, A/D converter, D/A con-
verter, clocks and general control circuits. (Refer to the main PCB diagrams, pages SVC 1 - 12 and
SVC 1 - 13.)
The functions provided by the new PC board are the same as those provided by the original HP 5890A
GC except that components have been added to control an additional heated zone and 2 AC valves.
The new board differs only in its implementation of these functions. The foremost change is the use of
a 68 pin PLCC custom IC which performs the same functions as do 26 TTL IC' s on the original
05890- 60010 board
SVC 1- 11
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