Service manual

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_______________ ---JI fi-5
DOUBLE-DENSITY DISK CONTROLLER .
IN CASE OF DIFFICULTY
If your system does not operate properly, make the following checks.
PROBLEM POSSIBLE CAUSE
Drive access light does not turn on when
1. Check for proper connections of floppy cable
disk is booted. inside Computer.
2. Check for proper connections of rear panel extension
cable inside Computer.
3. Be sure Z-37 or Z-87 is turned on.
4.
Check positions of J1 and J2 on Z-89-37 circuit board.
5. Check U550 for correct part and installation.
Drive access light turns on but drive makes
1. Check positions of J4 through J9 on Z-89-37
an unusual clicking sound. circuit board.
All disk access lights turn on and remain on.
1.
A cable is connected with marked edge
on the wrong side.
Two drives turn on when a boot operation is
1. Two drives have their disk selection jumpers
selected. programmed the same.
Computer only beeps once when turned on.
1. OFF LINE key in down position. Should be up.
2.
U550, U516, or U518 installed incorrectly.
3. 3" jumper wire installed incorrectly.
4.
16-eonductor cable with plugs installed incorrectly.
Computer will not accept boot command, returns
1. Be sure disk is installed in selected drive
to H: prompt, or starts to boot but does not before boot command is given.
return to H: prompt without reset.
2.
If H-88-1 disk I/O is not installed, check for proper
installation of the 4700
n resistor with connectors.