HP 8901B - Page 273

Service Model 8901B
Controller Kernel Check
MOS and CMOS ICs can be damaged by static charges and circuit
transients.
Do not remove the A13 Controller Assembly or the A14 Remote
Interface Assembly from the instrument while power
is applied. Discharge
the board and replacement
IC to the same potential. (Use a conductive
foam pad such
as provided in the Service Accessory Kit HP 08901 -60089.)
When unplugging ICs, place the board on a conductive pad. When the IC
is unplugged, insert it into the foam also.
A13 also contains a soldered-in battery. To prevent shorting out the battery,
do not lay the board on a metal surface.
Severai ICs on these assemblies are held in high-grip sockets. Both the
socket and the device can be damaged
if an attempt is made to remove the
device with an
IC extraction tool. The recommended procedure is to first
ground the tip
of a small blade-type screwdriver, then slide the tip between
the IC and the socket and slowly pry up the
IC one pair of pins at a time.
1. Switch POWER to STBY. Extend the A13 Controller Assembly with the Digital Test/Extender
Board. Switch POWER to
ON.
2. Check A13TP12 (+12V) with dc voltmeter. The voltage should be between +11.4 and -I-12.6 Vdc.
If faulty,
see Service Sheet 24 and check the +12V Regulator.
3. Short A13TP9 (RESET) to A13TP10 (+5V). This resets the Controller and forces a short write
(instruction) cycle. Connect a high-impedance, dc coupled oscilloscope
to A13TP4 (WRT) or the
WRT test point on the extender board. The waveform should be TTL pulses with a period of 2
ps. If faulty, see Service Sheet 24 and check the clock and (9 lines and the Power-On Reset circuit.
4. Set the ROMC switches on extender board to GND. This forces the SMI to step through its
addresses. On the extender board, connect the signature analyzer clipleads as follows:
Clock ................................................................................ WRT
Start
........................................................................ ADDRESS 15
Stop..
....................................................................... ADDRESS 15
Ground
.............................................................................. GND
5. Set the signature analyzer’s start, stop, and clock to trigger as follows:
..........................................................................
Start Falling Edge
Stop. .......................................................................... Falling Edge
Clock
.......................................................................... Rising Edge
6. Check the test points on the extender board with the signature analyzer probe as listed in Table
8D-15. If all signatures are bad except GND, see Service Sheet 24 and replace the SMI. If only
one ADDRESS line
is faulty, see Service Sheet 24 and check the SMI and the address line.
7. Check the RAM WRT and CPU READ test points on the extender board with an oscilloscope.
RAM WRT should be a TTL high, CPU READ should be a TTL square wave with a period of
2 ps. If faulty, see Service Sheet 24 and check the SMI and the load on the first two lines.
8. Switch POWER to STBY. Remove A13U1 (CPU External Register or RAM) from its socket.
8D-54 Service Sheet BD5