HP 82718A Service Manual page 24

HP 82718A
Troubleshooting and Diagnostics 5-3
Table 5-2. The HP-75 Does Not Ibrn On
Action
1. Remove the power PCA. (Refer to section 4 for disassembly procedures.)
CAUTION
Make sure there is nothing on your bench under the PCA, such as screws or washers, that could
cause a short circuit when power is applied. Otherwise, damage to the PCA may result.
CAUTION
When installing the extension cable, make sure the orientation of the cable at both ends is
correct. Otherwise, the PCA may be damaged.
Reconnect the PCA as shown in the picture below. Use the extension cable to connect the batteries
to the power PCA. The black wire on the extension cable goes to the outside when the connector is
pushed all the way onto the pins on the PCA.
Plug an ac adapter into the HP-75.
3. Go to table 5-3. Make sure that the batteries are fully charged and that the modem is turned off.
Check the voltages on the test points and replace those components that are bad as indicated by
incorrect voltages. Refer to the power supply schematic in section nine.
4. Press Iattn I. If the HP-75 does not turn on, remove the ROM connector from the PCA and plug it
into the HP-75.
5. Press \attn i. If the HP-75 does not turn on, the ROM connector is bad; replace it.
6. If the HP-75 turns on, the ROM connector is good. Reassemble it on the PCA.
7. Check the ROM-connector flex-cable connector and ICs U17, 18, and 19 for shorts or solder bridges.
Then ground test points 12, 10, and 8 one at a time in that order. While grounding each test point,
press IATTN i. If the HP-75 turns on, you have located the faulty IC. Replace the power PCA.
8. If the HP-75 does not turn on during step 7, replace the power PCA.