Tandy 6000 HD, Service Manual

Page: 189 / 416

Service Manual
TANDY 6000/6000-HD
TAN D Y COMPUTER PRODUCTS ----------------------------------------------------------------------
2. Visual Inspection
Check power supply for any broken, burned, or obviously
damaged components. Visually check the fuse. If any
questions, check with an ohmmeter.
3. Start-Up
Load power supply with minimum load as specified in
Table 7-5. Bring up power slowly with the variable
transformer while monitoring the +5 V output with the
oscilloscope and DVM. The power supply should start
with approximately 40-60 volts applied, and should
regulate when 95 VAC is reached. If the output has
reached 5 volts, complete a performance test as shown in
Section 7.3.5. If there is no output, refer to Section
7.3.4.
4. Bracket Removal
The main PCB is held to the bracket with screws and uses
spacers to separate the PCB from the bracket. An
insulator is inserted between the PCB and the mounting
bracket to ensure that the bracket cannot short any of
the pins of the PCB.
7.6.4. No Output
1. Check Fuse
If a fuse is blown, replace it but do not apply power
until the cause of the failure is found.
2. Preliminary Check on Major Primary Components
Check diode bridge (DBl), power transistor (Q7), and
catch diode (Q7) for shorted junctions. If any
component is found shorted, replace it.
3. Preliminary Check of Major Secondary Components
Use an ohmmeter to check for shorted outputs on the
various output lines. If the +5 V output is shorted,
check also crowbar SCR (SCRl) and zener diode (Zl).
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