Fluke 867B Revision L (manufacturing date 1998)My Fluke 867B died. I bought it used 10-15 years ago, so I don't know its history, but it was like new. No signs of abuse. I don't use it regularly, but I like to 'rotate' between the multimeters I've collected over the years. I've used it last around December and it was put back in storage in working order (batteries removed).
Yesterday I picked it up again, installed freshly charged batteries (6x Eneloop AA), and switched it on: The LCD backlight came on, but that's all. No graphics/text on the display. No clicking from the buzzer or relay. None of the positions on the mode dial have any effect, nor does pressing any of the buttons.
It's not just the LCD display or driver that is dead. I know the multimeter is supposed to make clicking noises at startup and between certain mode dial positions. Also when I dial it to Ohms, I measure no voltage on the sockets. So, there's a lot more wrong than just the display...
Luckily the Fluke 867B dates from the days public service manuals were still a thing:
Fluke 863/867B Service Manual (4.5 MB)
Chapter 2-2 covers the start-up sequence:
The GMM sequences through the following steps when power is applied:
• The 3.3V power supply comes up.
• The reset pin on the microprocessor (U25-1) goes high.
• The microprocessor (U25) begins executing the program stored in EEPROMs U11 and U19.
• LCD controller (U13) data is initialized.
• VEE is turned on (-20V dc), and the display comes on.
First I checked the power supplies: VCC/VAD (3.27V), VDD (5.2V), VSS (-5.2V). All are fine and well within tolerances with regards to voltage and ripple (chapter 2-6). Power consumption is normal.
PS: If you power an 867B with a lab power supply (7.2V at the battery terminals), make sure to set the current limit to at least 700 mA. Even though the multimeter draws 'only' ~200-250 mA under normal operation, the startup surge current is a lot higher. When the current limit is set too low, the 867B power supplies do not start properly. It looks as if there's a short somewhere pulling down the output voltages. I wasted a couple of hours chasing ghosts.Next I checked the reset pin on microprocessor U25 (
Hitachi H8/510): About 130 ms after switching on, the pin goes high (and stays high until powering off).
After this the microprocessor should start executing the program in the EPROMs. I checked this by monitoring the address lines on the U11 and U19 EPROMs. And here's a problem: There is no activity at all on the address lines.
So, the microprocessor does not run. Why? I checked pin 98 (EXTAL) on microprocessor U25 and there is no clock signal while there should be a 9.6 MHz signal.
According to the service manual the clock signal is provided by gate array U24 (chapter 2-49). The chip has an external 19.2 MHz crystal and divides this clock to generate different clocks for different parts of the hardware (this is just one of the things U24 does - it's quite an important chip in the circuit).
I confirmed U24 gets power, but there's no activity around the quartz crystal. From as soon as VCC is available, U24 pin 31 (XTAL1) goes high (3.27V) and pin 32 (XTAL2) stays low (0V). There are no oscillations.
U24 appears to be a custom chip made by NEC for for Fluke (Fluke part number 928671). There is no datasheet available.
And this is where I am currently stuck. Is it likely that U24 is dead? Or might the crystal be bad (do crystals even die - I never dropped the meter)? Does anyone have suggestions for further troubleshooting?