Fluke 900 - Manual (Page 91)

FLUKE 900 SERVICE MANUAL Maintenance
-2 -1
15
(U-L for pin 2) - (D-L for pin 15) = -2 -1 = -3 (failure)
This means that one of the 74ALS09 chips in FI or F7 may have the saturation
voltage at its output (Vol) too small or too big compared to the rest of ’09s. The Vol
can be measured by disabling Clip Check and RD Test and running a continuous test.
From the main screen, proceed as follows:
- Press ES(manual) to go into Manual Mode
- Select a 28 pin device. Press EI)(local) ©(size) ©® [
enter ).
- Set t_time to continuous. Press I etcj (Ei)(t_time) Sl(cont.) [ enjer j.
- Press IM) to go back to the Manual menu.
- Disable RD Test. Press El(rd) El(rdt_off) .
-Disable Clip Check. Press (O(clip) £D(clip_chk) (ED(on/ofO [ enter
)(^),
- Insert a 28 pin Test Clip into the Interface Buffer and press [ test ] .
- Measure, with a DVM, the voltage on the 74ALS09 outputs (it is enough to
measure only one output per chip). Note that, for lines 14 and 28, the voltage will be
zero because these are power supply lines for the 28 STD size).
74ALS09 chips are classified at the factory according to Vol rating and marked with a
colored dot as follows:
Vol (mV) group marker
96 - 135 A white
136 - 174 B orange
175 - 212 C green
213 - 251 D blue
252 - 290 E red
291 - 329 F brown
Although these ranges cover aU the possible values listed by vendors, it has been
found that the normal range of Vol is from 136 to 212. AU machines built up to the
end of 1992 have 74ALS09 devices with orange or green dot markings.
AU 74ALS09 chips on the board have to be from the same group, so the device with
Vol too big or too smaU must be replaced with a properly rated 74ALS09.
After replacement, the caUbration procedure should be restarted. If there is no need
to replace a chip, go to Section 5.4.2.6.3
5.4.2.6.3 Selftest buffer and 86 gate related condition
The channels with a ">" character in any block should be checked to see if they meet
the foUowing conditions:
5 - 1 3