HP 5334B Service Manual page 182

I
INSPECT 2 BLACK
THERMISTOR LEADS
WHERE THEY ENTER
I
OVEN
PROBLEM
m
-
1
CHECK OVEN POWER LINE
CONNECT A SHORT
FOR SHORT TO OVEN
JUMPER OR CLIP LEAD
INDICATES FAULT IS IN
BOARD FOR BROKEN
CONNECTIONS.
REMOVE TOP COVER
(SEE PARA. 8-397)
ALLOW OSCILLATOR TO
COOL 1 HR.
I
INDICATES OVEN HAS
OVERHEATED OR F1
ACROSS R36. THlS
MASS OR OVEN COMMON.
CURRENT LIMIT CIRCUIT
GROUNDS 0 6 1 BI AND
CHECK 0 7 AND 0 8 FOR
OF UlB/CR6. TROUBLE-
SHOULD TURN OFF,
CONTACT SHORT TO
SHOOT THlS CIRCUIT.
OVEN MASS.CHECK 06.7,8 06. 7. 8
I
A
DEFECTIVE. REPLACE OR
TEMPORARILY JUMPER
F1. CHECK TO BE SURE
POWER SUPPLY IS SET TO
1. OPEN THERMAL FUSE
2. OVEN HEATER CIRCUIT
TURNED OFF BY DEFEC-
TIVE COMPONENTS
1
FOR C-E SHORT
USING A SHORT CLlP
LEAD OR JUMPER.
CONNECT TO RT1 IWHERE
IT CONNECTS TO R221 TO
CONNECT +20V TO OVEN
CONTROLLER CIRCUIT
ONLY. SET CURRENT
LIMIT ON POWER SUPPLY
TO 600 mA. TURN ON
SUPPLY ONLY LONG
ENOUGH TO DETERMINE
CURRENT.
THE NEARBY GROUND
I
POST. THIS SHOULD
I
LEAD OR JUMPER.
CONNECT RT1 IWHERE IT
CONNECTS TO R221 TO
POWER AND
THE NEARBY GROUND-
>4.5K
)
POST. THIS WILL CAUSE
.
THE CIRCUIT TO
ATTEMPT TO TURN OFF.
TURN ON POWER SUPPLY
CAUSE THE CONTROLLER
TO TURN OFF.
O N POWER
>480
f i
SUPPLY AND
MEASURE OVEN
CURRENT.
ONLY LONG ENOUGH TO
DETERMINE CURRENT. "NORMAL" VOLTAGES
FOR RT1 SHORTED TO
GROUND. TROUBLE IS
TABLE 8-11 GIVES
"NORMAL VOLTAGES
FOR RT1 SHORTED TO
GROUND. CIRCUITS OF
U1A. U2 PROBABLY OK.
TROUBLESHOOT U3 AND
TEMP. SENSE BRIDGE
CIRCUITS INCLUDING 10V
FROM U2.
--+
I
CR6, R31. 32, 38. AND 39
CHECK OPERATION OF
I
THIS CIRCUIT USING
1
NORMAL WARMUP
VOLTAGES GIVEN IN
TABLE 8-1 1 LOW CURRENT
CAN ALSO BE CAUSED BY
TEMP SENSE CIRCUIT OF
RT1 AND U3. CHECK 10V
SUPPLY AT U2
PROBABLY IN CIRCUITRY
TURN ON POWER SUPPLY
> O mA
OF 06. 0 7 . 08. TROUBLE-
ONLY LONG ENOUGH TO
SHOOT THESE CIRCUITS
DETERMINE CURRENT RT1 SHORT FIRST STARTING WITH Q6.
SEE NOTE 2
TURN OFF POWER SUPPLY
AND REMOVE RT1 SHORT.
TO =I50 mA OR LESS
TURN O N POWER SUPPLY
I
WARMUP CURRENT IS
7 3 8 0
-
480 mA
USE TABLE 8-1 1 WHICH
LISTS WARMUP OVEN
CONTROLLER VOLTAGES.
EXIT SIDE OF
R17 10V 2 .l0/o
CHECK 0 6 COLLECTOR
AND EMITTER VOLTAGES
FIRST
-
-
TROUBLE IS PROBABLY
OPEN THERMISTOR AT1
OR ITS CONNECTION
INTO CIRCUIT. RESIST-
ANCE OF RT1 SHOULD BE
LESS THAN 9.95K AFTER 10
MINUTES OF OPERATION
CHECK 10V SUPPLY AT U2.
DOES OVEN
OVEN,
CHECK: 0 7 FOR C-E
SHORT. U l A 171 FOR
ALWAYS-HIGH
CONDITION
NOTES:
1. THE 5.2K
11
VALUE IS
NOMINAL. A SHORTED
0 7 OR 0 8 BRINGS THlS
VALUE VERY LOW. AN
OPEN 0 7 OR 0 8 WlLL
INCREASE THlS VALUE.
THE POLARITY OF THE
OHM-METER WlLL ALSO
CHANGE THlS VALUE.
2. THE OVEN MAY HAVE
WARMED UP DURING
PREVIOUS TESTING.
ALLOW OVEN TO COOL
FOR 5-10 MINUTES
BEFORE PROCEEDING.
Figure 8-10. Troublesltooti~tg Tree
HP 5334B
-
Service Manual
8-61