Fluke 2635A, 2625A service manual Review

HYDRA

Service Manual

REVIEW	REM	SCAN	SET	FUNC
				mV	k Ω			EXT TR
				x1		1
								s41f.eps
		Figure 5-10. Display Test Pattern #1
	MAX		Mx+B	ALARM		F
LAST	MIN AUTO	MON
				°C	°F RO
				AC DC		LIMIT	HI	OFF PRN CH
				M	Hz	2	LO	CAL

s42f.eps

Figure 5-11. Display Test Pattern #2

When a Hydra display is initially powered up, all display segments should come on automatically. If this display does not appear, proceed with the following steps:

Note

If the display is operational but has problems whenfront-panel buttons are pressed, proceed directlyto step 9.

1.Check the three power supplies with respect to GND (A2TP3 or A2U1-42) on the Display Assembly.

∙VCC (A2U1-21) 4.85 to 5.35V dc

∙VEE (A2U1-4)-4.75 to -5.25V dc

∙VLOAD (A2U1-5)-28.5 to -32.0V dc

2.Check the filament drive signals FIL1 and FIL2; these connect to the last two pins on each end of A2DS1. These signals should be 5.4V ac with FIL2 biased to be about 6.8V dc higher than the VLOAD supply (nominally a -23.2V dc level). FIL1 and FIL2 should be 180 degrees out of phase. If the dc bias of FIL2 is not at about - 23.2V dc, the display segments that should be "off" will show a shadowing (or speckling) effect.

Note

It may be necessary to disable the watchdog resetby jumpering A2TP1 (A2U5-3, A2U5-11) to GND (A2TP3) toverify the following items.

3.Check the clock signal CLK1 at A2TP2, A2U1-2, and A2U4-3. This signal should be a 614.4-kHz square wave (1.628 ms per cycle). This signal depends on an E clock signal of 1.2288 MHz from the Hydra Main Assembly. If the E clock is 819.2 kHz (1.221 ms per cycle), it is possible that SWR2 (A2J1-16) is shorted to ground, causing the Microprocessor to HALT at power-up.

4.Check the state of the RESET signal (A2U1-1). This signal should be low once the reset time is completed (after power-up). Also verify that the RESET* signal (A2U6-3) is high after the reset time is completed.

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