Wyse WY-60 Maintenance Manual page 40

Figure 3-1 Troubleshooting Flowchart, page
4
of
1
No Video/No Beep, Continued
8. Chec k U9
(continued)
If U9 is being addressed by Ul, but
U9 is not toggling, replace it.
If interrupts are active, but not
toggling, go to step 9.
If interrupts are active and
toggling, check the soft font data
path, U19- CO to C7.
Check MBC output: If there is no
output, check Ul, all read/write
and data connections.
If no output and selection
functions occur, replace U9.
Check HSYNC output U9-19.
26.58 KHz.
Look for
9. Check Ul
Chec k po wer to U1.
ground.
Ul-40, Ul-20 is
Check the processor clock: Ul-18,
Ul-19, and connected circuitry
including X4, Cl0, and Cl1.
Check signal PSEN, Ul-29 to U6-22.
If there is no activity present,
check U6, U7, U4, Ul, their
interconnections and all address
and data busses connected to U1.
Check signal ALE, Ul-30. Look for
a signal at 1/12th the clock rate.
If this signal is not present,
check the reset line Ul-9, and the
processor clock, Ul-18 and U1-19.
Check U1-1. In standard operation
in 80-column mode, this pin is low.
If PSEN and ALE are functioning and
this line is high, check all
address and data busses.
Is U6 plugged into its socket
backwards?
3-9