Fluke 2625A 5A-14. Digital Kernel Troubleshooting, Ohms Open-Circuit Voltage 2635A Range

HYDRA

Service Manual

Table 5A-6. Ohms Open-Circuit Voltage (2635A)

Range

300Ω

3kΩ

30kΩ

300kΩ

3MΩ

10MΩ

Voltage

3V

1.3V

1.3V

3V

3V

3V

Table 5A-7. Ohms HI Troubleshooting (2635A)

Checkpoint

A3U8 pin 14

A3R10 HI SRC

Channel HI

A3U8 pin 23

A3U8 pin 58

Signal Description

Ohms Source

Ohms Source

Ohms Source

Ohms Source

Ohms Source filter output

Possible Fault

A3U8

A3R10, A3K16, A3RT1, A3Z4, A3Q10

A3K1 through A3K14, A3U4, A3U5, A3U11, A3U12, A3L1, A3L2, A3L3

A3R11, A3K17, A3R42, A3C32

A3U8, A3Q2

5A-14. Digital Kernel Troubleshooting

At power-up, if the display does not light or lights up and fails to report errors or begin operation, use the following troubleshooting procedures.

To determine the relative health of the MC68302 Microprocessor (A1U1), first check for a valid system clock (SCLK) at TP11. Use an oscilloscope to check for the SCLK clock at A1TP11. Look for a 12.288-MHz square wave that transitions from 0 to 5V dc (VCC).

∙If this signal is present, check for a similar waveform at pinA1U25-30 of the FPGA. If a 12.288-MHz square wave is not presentthere, resistor A1R107 is probably bad.

∙If the SCLK signal (A1TP11) is something other than a 12.288-MHzsquare wave, it is most likely that the problem is related to thecrystal oscillator circuit (A1U1, A1Y1, A1C3, A1C8, or A1R2).

If the SCLK signal is good, check the Display Clock (DCLK) output from A1U25-19. DCLK should have a frequency of 1.024-MHz (period of 976 nanoseconds). The DCLK signal is not symmetrical; use an oscilloscope to verify that it is high for about 325 nanoseconds and then low for about 651 nanoseconds. The operation of the Display assembly depends on the DCLK signal. Missing segments, intensified digits, a strobing display, or a blank display can be caused by a faulty DCLK clock.

∙If the DCLK signal (A1U25-19) is not present but the SCLK signal iscorrect at A1U25-30, the problem may be that A1U25 was notconfigured correctly at power- up or A1U25 is defective.

∙If the OCLK signal (A1U25-22) is a 3.072-MHz square wave but the DCLKsignal is wrong, A1U25 must be defective.

5A-18