Master Series Service Manual
4 Are the connector pins in good condition? If not, the fault could
show itself as intermittent operation.
5 Check the 1.23MHz connection to the ACIA.
7.7.2 Will not load data.
1 Check 1 3 and 4 above.
2 Check that the ACIA is receiving an Rx CLK, IC45 pin 3.
2 Check the connections between the SERPR0C IC48 and ACIA IC45.
3 Check that incoming data is appearing at the pin at the back of the
connector.
4 Follow the signal path through the high and low pass filters. It
should finish up as a 1.2V peak to peak signal at the CASIN input to
the SERPROC, IC48 pin 12. If it disappears at any point there is
probably a dry joint.
5 The cassette data input has a static protection network on it. Check
that all the components in this are fitted and have the correct
values. A faulty component could mean that the LM324 has been
subsequently damaged.
6 Check that the ACIA and SERPR0C have correct (i.e. no open or short
circuit) connections on all pins.
7 Check the 1.23MHz connection to the ACIA.
8 As a last resort, change the SERPR0C and try again, then try the
ACIA. This should not be necessary as both of these components are
very reliable.
7.7.3 Will not save data.
1 Check the cable and data recorder (with another computer if
possible).
2 Check that the ACIA is getting a Tx CLK, IC45 pin 4.
3 Check the connections between the SERPR0C and ACIA.
4 Check that the back panel connector has no dry joints or short
circuits between it and the interface circuitry.
5 Are the connector pins in good condition? If not, the fault could
show itself as intermittent operation.
6 Check that data is coming out of the CAS0UT output from the SERPROC,
IC48 pin 27. If not, check all the data and address connections to the
SERPR0C and ACIA.
7 Follow the signal (if it exists) from the SERPR0C to the connector.
If it disappears then a dry joint or short to power or ground is
likely.
43
Issue 1
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