HP 6038A, Service Manual

Page: 52 / 111

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Table 3-10. Performance Failure Symptoms
DEFECTIVE
SYMPTOMS BOARD CHECK FUNCTIONAL CIRCUITS
unexplained OVP shutdowns A2 OVP circuit, CV circuit
no current limit A2 CC circuit
max current < 10Adc (6038A)
< 30Adc (6033A) A2 CC Clamp, CC circuit
max power < specified A2, A1 Power Limit, 20KHz clock, transformer AlT1
max voltage < 60Vdc (6038A)
< 20Vdc (6033A) A2, A1 CV Circuit, diodes A1CR1-CR4
cycles on & off randomly A2, A1 AC-Surge-&-Dropout Detector, Mains Voltage
Select switch A1S2
CV overshoots A2 A2U10A, A2CR20, A2R94
output noise (<1KHz) A2,A1 CV circuit, input filter
output noise (>1KHz) A1, A4 transformer AlT1, Output Filter, snubbers
A4R7/R8/C5/CR5/, A4R13/
R14/C6/CR6, A4R33/C13
CV regulation, transient A2, A1 wrong sensing
response, programming time low ac mains voltage, CV circuit
CC regulation A2 low ac mains voltage, CC circuit
CV oscillates with capacitive A2 A2R10, A2C51, A2R95, A2R96, A2R86,
loads A2C47, A2R71, A2C36
CC oscillates with inductive A2 A2U10, A2R86, A2C47, A2C43, A2R77, A2U3D
loads A2U3D, A2R30, A2C44, A2R76, A2R75,
A2C42, A2C41, A2R1
Table 3-11. No-Output Failures
(Bias supplies and AC turn-on circuit functioning)
Status of FET On/Off-Pulses
PWM-ON
A2J3-26
PWM-OFF
A2J3-25
DEFECTIVE
BOARD CHECK FUNCTIONAL CIRCUITS
Lo Lo A2 Control ckts: CV & CC thru On- & Off-Pulse Oneshots *
Lo Hi A2&A4 PWM and DC-to-DC Converter: A4Q3 and A4Q4 probably failed
Hi Lo A2&A4 PWM and DC-to-DC Converter: A4Q3 and A4Q4 probably failed
Hi Hi A2&A4 PWM and DC-to-DC Converter: A4Q3 and A4Q4 probably failed
Lo N A2 A2U17B, On-Pulse Oneshot and A2Q6A
N Lo A2&A4 Off-Pulse Oneshot and DC-to-DC: A4Q3 and A4Q4 probably failed
Hi N A2&A4 A2U17B, On-Pulse Oneshot & DC-to-DC: A4Q3 and A4Q4 probably
failed
N Hi A2&A4 Off-Pulse Oneshot and DC-to-DC: A4Q3 and A4Q4 probably failed
N N A2&A4 Power-Limit Comparator and DC-to-DC: A4Q3 and A4Q4 probably
failed
Lo= TTL low Hi= TTL high N= normal 20KHz pulse train, TTL levels
* Decide which to troubleshoot--the CV circuit, the CC circuit, or the PWM and Off-Pulse & On-Pulse Oneshots-- by
measuring the CV CONTROL (A2CR24, cathode) and the CC CONTROL (A2CR19 cathode) voltages. Troubleshoot
whichever is negative, and if neither is negative, troubleshoot the PWM. Make these voltage measurements after you
have implemented the Main Troubleshooting Setup.