Maintenance
6–38 THS710A, THS720A, THS730A & THS720P Service Manual
PROBE COMP Output. When the instrument is on, the PROBE COMP output
should generate a square wave, approximately 5 V in amplitude, at a 1.2 kHz
frequency. Use the oscilloscope and a 10X probe to probe this output. If the
signal is not present, the main board is probably defective. Replace it.
RS-232 Port. Verify that the RS-232 port operates properly. The easiest way to
test the port is to make a hard copy with a compatible printer and RS-232 cable.
To prepare to make a hard copy, verify the following statements:
HThe printer is compatible with one of the supported formats: Deskjet,
DPU 411/II, DPU 412, Epson 9-pin, Epson 24-pin, Laserjet, or Thinkjet.
HThe printer is equipped with a serial (RS-232) port.
HThe printer is connected to the instrument through a known good RS-232
cable and adapter (if needed).
HThe printer is powered on and paper is loaded.
HThe printer baud rate setting is known.
Set up the instrument and start the hard copy with the following steps:
SCO
PE
UTI
L
ITY
System RS-232
—
Set RS232 Param-
eters To Defaults —
Baud rate — Set baud rate to
match printer baud
rate
System Hard Copy
—
Format Choose format to
match printer1
OK Select Format
—
HARD COPY —
1You may need to press Select Page to display additional printer formats.
If the RS-232 port is defective, replace the main board.