Zenith Z-100 PC series Service Manual page 293

Page
4.7
Troubleshooting
Table 4.2. Floppy Disk Controller Component Failures
SYMPTOM
No controller
indication
Drive motors
will not turn
on
Driver motors
come on but
do not stay on
Erroneous data
from good disk
Bad card
addressing or
selection
Read sector
errors
Precomposition
Erroneous data
Will not write
SUSPECTED PARTS
U348
U305
U302,U307
U320, U321
U321
Power supply
U301, U320, U321
U303
U304
U305, U308, U313
U338
U302
U305,U310,U314,U315
U306, U311, U317
U304,U314,U315
U305, U308
THINGS TO CHECK
Bus interlace.
FDCIC.
Signal buffers.
Logic gates.
Signal decoder.
Check pulse width after
last access. It should last
2-3 seconds.
Read data buffer/inverter.
Data separation Chip.
Read errors entering memory.
Incorrect DMA signals causing
incorrect processing of data.
Check DMA processor on CPU card.
PAL address decoder. Refer
to PAL equations in Chapter 3
for I/O signals.
Check for proper lOX Signal.
Check for correct precomp.
signals (early, late).
Check clock frequencies.
Check for correct Signal
pulses.
Check write gate enable
signal.