Omron 8025G Maintenance Manual page 170

MAINTENANCE AND REPAIR
SECTION 6
Refresh Memory Card. Do not perform bench maintenance on this card. Re-
place with an operational card and return the faulty card to OMRON for repair.
Program (PROM) Memory Card. Do not perform bench maintenance on this card.
Replace with an operational card and return the faulty card to OMRON for repair.
Keyboard Card. Except for key switch and encoder replacement (refer to
Pgragraph 6.2), do not perform bench service on this card. Replace with an opera-
tional card and return the faulty card to OMRON for repair.
Motherboard. Do not perform bench service on this board. Replace with
an operational board and return the faulty board to OMRON for repair.
LED Assembly. Except for damage to the printed circuit card, a non-
operational LED (light emitting diode) is the only malfunction that can exist in
this assembly.
To test LEOs, apply 5 V dc to pin 8 or 9 of P24. Then individually ground
the cathode of each LED. Replace any LED that does not turn on. If an operational
, LED does not turn on under normal terminal operation, the problem is probably on
the Refresh Buffer Card.
Power Supply Assembly and Regulator Card. Basic power supply and regula-
tor circuitry is used in the terminal. Use standard voltage and resistance measure-
ment techniques to isolate problems in these two sections.
Terminator Card. The Terminator Card consists of five integrated-circuit
resistive networks (Xl through XS). A malfunction in a network is detected by mea-
suring the res~stance between pin 16 and each of the other pins (1 through 15). The
readings should be 330 ohms on Xl through X4 and 470 ohms on XS.
CRT Display. Once a malfunction is narrowed to the CRT Display section,
the fault can be further isolated to a circuit and component as follows:
NOTE: Before troubleshooting the CRT display, be sure the problem
is not caused by incorrect adjustment settings (refer to
Section 7) or absence of terminal inputs to the display.
1. Many malfunctions can be narrowed to a section or circuit by analyz-
ing the display presentation. When you are able to locate the pro-
blem area with this technique, proceed to Step 3.
2. Measure +55 V dc. Connect the positive lead to the cathode of CRI06
and the negative lead to ground.
NOTE: If +55
V
dc is correct, go immediately to Step 3.
a. If the voltage is too high, Ql13 may fire erratically and cause
raster "tearing".
b. A short
ci
rcui t causes
the
regul ator to "foldback" to 1 imi t the
current. Thi~ condition is indicated by a low or zero voltage
at the cathode of CR}06.