Radio Shack CCR-81 Reference Handbook

stall each RAM until you find one that crashes
the power supply. Remove the bad RAM and
continue to check the rest of them. There may
be more than one shorted device.
A
short on the +5 volt bus can be a real head-
ache. Unless
you can see the short, you will have
to cut runs to Section Isolate. Once you isolate
the shorted section, you will probably still have
to make other cuts to get down to the short. Do
not forget to repair your cuts. And remember,
these runs must carry considerable current. Use
stranded or solid wire (22 gauge or larger) to
repair cuts. (Never solder-bridge an etch cut;
simple Board stress may open the solder-bridge
or tear small runs loose from the Board.)
If you find a dead
+12 volt bus, examine 01 's
heat sink. The hardware holding the transistor/
sink sandwich together may have loosened. The
heat sink may have turned around and shorted
against 01' s base or em itter lead. Depending on
the force, it might have sheared one or more
leads from
the PCB. If you find a loose heat
sink. shorted or not, retighten it.
Problems with
the AC adapter are usually termi-
nal. Either the fuse link in the primary winding
has
opened, or the wires were destroyed at the
male DI N plug. If you find the fuse link blown,
check rectifier package CR8 for shorted diodes.
In
any case replace the adapter.
Figure 19 lists the voltages found around Z1 and
Z2 for a normal operating unit. The +12 volt
supply has been adjusted for 12.00 volts and the
-5 volt supply has been adjusted for 5.00 volts.
Z1
Z2
Pin Number
Voltage
Pin Number
Voltage
1
0.00 1
0.00
2
5.30
2
10.60
3
5.00
3
11.99
4
5.00
4
6.92
5
5.00
5
6.92
6
7.46
6
6.92
7
0.00 7
0.00
8
0.00
8
0.00
9
0.33
9
5.72
10
5.89
10 12.31
11
11.99
11 21.16
12
11.99 12
21.69
13
7.05 13
13.48
14
0.00 14
0.00
All voltages are measured with a digital volt-
meter. Voltages
are referenced to ground at the
right side of capacitor e9.
FIGURE 19. Table ofPower Supply Voltages for Zl and Z2
75

Radio Shack CCR-81 Specifications

General

Brand	Radio Shack
Model	CCR-81
Category	Desktop
Language	English