Diagnostic Testing and Troubleshooting (2635A) 5A

Power Supply Troubleshooting

5A-9. Inverter

Use an oscilloscope to troubleshoot the inverter supply. The outputs of the inverter supply are -5V dc (VEE), -30V dc (VLOAD), and 5.4V ac (FIL1 and FIL2) outguard, and +5.3V dc (VDD), -5.4V dc (VSS), and +5.6V dc (VDDR) inguard. Refer to Figure 5A-3. The signal at the drains of the two inverter switch FETs (A1Q7 and A1Q8) should be a 10V peak square wave with a period of approximately 18 us. The gate signal is a 5.1V peak square wave with rounded leading and trailing edges. The leading edge has a small positive rounded pulse with an amplitude of 1.8V peak and a pulse width of about

0.3us. The signal at A1U22-5 and A1U22-6 is a symmetrical square wave with an amplitude of 5.1V peak and a period of about 18 us. The negative-going trailing edge of both square waves is slower than the rising edge and has a small bump at about 1.5 volts. The signal at A1U22-3 (TP14) is a symmetrical square wave with a period of about 9 us.

For the inverter to operate, the 110-kHz oscillator must be operating properly. If the signal at A1U22-3 is missing, begin by checking the voltage at A1TP7. The voltage should be about +5.3V dc. Then, using an oscilloscope, check for a square wave signal at A1U23-9 and a square wave signal at A1U23-8. If the FETs are getting proper drive signals, failures that heavily load the inverter supply will usually cause the inverter to draw enough current to make the switcher supply go into current limit. Shorted rectifier diodes and shorted electrolytic capacitors will cause heavy load conditions for the inverter.

U9-7 and T2-2

20V

0V

5V/DIV

2 ∝S/DIV

Normal Load

s33f.eps

Figure 5A-2. 5-Volt Switching Supply (2635A)

5A-9

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Fluke 2625A service manual 5A-9. Inverter, Volt Switching Supply 2635A
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2635A, 2625A specifications

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