Maintenance—2246 1Y and 2246 Mod A Service
Table 6-9, (cont)
Measurement Error Troubleshooting Hints
Circuit
Problem
Symptoms
RO FREEZE line stuck
high (U173-11)
Gross cursor problems for Types 2, 3, and 4 measurements.
Gross cursor problems for A TL and B TL.
Gross valve problems with Type 1 measurements.
Test: Monitor during CH 1/CH 2 VOLTMETER menu SELF CAL. Signal
line should reach TTL low.
VERTICAL PREAMP AND OUTPUT AMPLIFIER (schematic Diagram 2)
Preamp Trig Outputs
Bad
Gross value problems for Types 2, 3, and 4 measurements for
affected channel.
Test: Check B triggering on the affected channel.
Preamp Vert Outputs or
Enable Bad
Gross cursor problems for Types 2, 3, and 4 measurement for
affected channel.
Gross value accuracy problems for Type 1 measurements for
affected channel.
Test: With only the affected channel selected for display, check
that channel is shown and check gain accuracy.
VERT COMP output
(U702-7)
Gross value problems with Type 1 measurements.
Gross cursor problems with Types 2, 3, and 4 measurements.
Gross cursor problems with A TL and B TL.
Test: Lift W1101 and ground the base of Q703. VERT COMP
should be toggling between TTL high and TTL low either with readout
on or with two channels on (one at screen top, one at screen bottom).
A AND B TRIGGER SYSTEM (schematic Diagram 3)
A Trig Source
Multiplexer (U421A)
“ SEARCH FAILED AT 5 |is ” for “ SELF CAL” on time measurements
unless stuck in LINE.
Minor to gross value problems (depending on which source is
stuck) with the A TL measurement.
Test: Set A Trigger SOURCE to VERT.
For each channel, display only that channel and check that the
signal applied to the displayed channel appears at pin 25 of
U421.
Summary of Contents for 2246 1Y
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