Troubleshooting Flowchart; No Video/No Beep - Wyse WY-60 Maintenance Manual

Figure 3-1 Troubleshooting Flowchart, page 2 of 7
No Video/No Beep
1.
Check power cord,
on/off swi tch,
fuse
Check for continuity and correct
connections.
Make sure J102 is set for the
correct line voltage.
2. Check beeper B1 and
surrounding circuitry
3.
4.
5.
6.
7.
Check brightness
Check all power
supplies
Check tube filament
Check video
transistors
Check U20
Check the brightness slideswitchj
perform the brightness alignment.
(See "Brightness" in Chapter 4.)
+5V, U1-40, (U1-20 is ground)
+12V, U27-14 (U27-7 is ground)
-12V, U27-1 (U27-7 is ground)
If one of the power supply vol tages
is out of tolerance, use the
schematics found in Chapter 7 to
trace and fix the problem.
Is it glowing? If not, check the
tube socket:
Is the socket plugged in?
Are any of the CRT's pins bent?
Check the continuity between the
socket and its board connections.
Q402, Q401, Q403, Q404. If any
aren't operating correctly, replace.
Look for video output:
Video 0, U20-14
Video 1, U20-15
Check both lines with an
oscilloscope, you should see
toggling activity on both. If you
don't, check these areas:
Dot Clock at U20-1. Look for a
50 percent duty cycle at 26.58 or
39.71 MHz.
If the waveform is missing or
incorrect, re~ove U20 and
tro ubl eshoo
t
the dot cl oc k. Chec k
U21 and the surrounding circuitry.
Then check U20-1 again.
3-7