Electronics > Repair
Fluke 289 not quite sorted.
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kjk24:
Hi nixxon,

the Regulator until the lcd show the regular application is off, u17 is switched on from MSP430 when the app is running (LCD shows it)
it has prop nothing todo with the error message.
check if the bootloader can load the app. by connecting rs232 and bootloader jumper..... see older posts.
MihaiV:
Hello everyone,

I saw a cheap and faulty Fluke287/NUC on ebay. The seller said it shows the leads connection error on any setting, so I went for it.
A different meter with a different fault arrived, and the other one was already gone. Shipping it back would have been more expensive than the unit itself, so I kept it.

At power-up, it lights the led for 1 second, than it blinks very shortly and it make an extremely short beep, it displays the Fluke logo and the led turns off (as it should) and the screen goes gray when it should display its measurements.

No button is active, switching functions does nothing and it can only be turned off by removing the batteries.

On some occasions the display does not turn on at all.

Let's inspect: no damage at all on the case, the screen has its protection foil on. Input terminals clean.
Inside: no sign of input damage: MOVS have "infinite" resistance, PTC, 1K resistor and the high voltage resistor are ok. The fuse is missing though... The board is clean, no sign of fluid damage anywhere. It appears someone was here before: the screws from the input terminals indicate that an unsuitable screwdriver was used to remove them.

Anyway: the back-up capacitor was a bit corroded but it did not leak. I removed it.
I measured all power rails for shorts: the 21V for the LCD, the 3.3V for MSP, the 1.8V and the 2.9V, the 5V and the 2.5V reference, and finally the LCD display outputs from the LP324. I found none. Next, I checked all jelly-bean semiconductor: all diodes (CR and VR) and all transistors (from the posts above), are ok, no shorts, no obvious conduction in both ways.

Now apply power: 9V through the battery pads. I see the 3.2V for the MSP is on and all capacitors around it measure the same, except C41. This is the external ADC reference input, taken from the voltage reference. No other voltage is present on any other test points and caps.

Power on:
- The dual buck provides 2.94V (158KHz switching frequency, 98% duty cycle, 0.958V at the feedback pin) and 1.8V (300KHz switching, 92% duty cycle and 0.904V at the feedback pin).
   
- The 21V boost converter is on and U19 (LP324) provides voltages close to the ones from the previous posts: 1.31V, 2.62V, 18.55V and 19.8V. While at it, I also checked the opa-mp operation but there was no significant difference from the inverting and non-inverting inputs (<1mv)
   
- U17 outputs only 0.58V... But it is not faulty, it is disabled by the MSP. I checked that trace and it is not shorted to VCC. So, no 5V and no 2.5V reference output. No other voltage is present on any capacitor in the analog section, including the ADC.
   
- A look with a thermal camera didn't show anything. The 2.9V + 1.8V converter and the MXS were barely showing up, everything else was cold.
   
After several power-ups, I noticed that the display only operates when my hand is near the main processor, U26. Pressing lightly on it made the display show the logo every time. So I reflowed it (and the Flash + RAM chips while at it) at the university with a dedicated BGA rework station, and that partly fixed the problem. The display shows the logo every time.

But the display still becomes gray after the logo and the led. What I noticed is that after removing the power, a single horizontal line briefly remains on the display, fading away in less than 1 second. So it appears it continuously sweeps the screen, making it gray.

Here is what I measured on the LCD connector:
   1. 21.1V constant.
   2. 19.26V constant.
   3. 18.55V constant.
   4. 2.62V constant.
   5. 1.32V constant.
   6. 0V
   7. 0V
   8. 2.94V constant.
   9. Square wave, 171Hz, 50% duty cycle, 3V logic.
   10. Square wave, 75Hz, 0.8% duty cycle, 3V logic, appears to be a syncro signal.
   11. Square wave, 18.1KHz, 3.6% duty cycle, 3V logic.
   12. 2.94V constant.
   13. Square wave, 1.67MHz, 50% duty cycle, 3V logic. Looks like a clock signal.
   14. 0v
   15. 0V, goes towards the MXS.
   16. 0V
   17. 0V, goes towards the MXS.
   18. 0V
   19. 9V (from supply)
   20. 0V, connected to the collector of Q17. Appears to be the cathode of the backlight.
   
The LCD itself appears ok, since it correctly displays the Fluke logo. The ribbon cable looks good to, no sharp bends or interruptions.

I also checked the crystals: the MSP 32.768KHz crystal resonates near enough (32.77KHz), with 200mVpp.
The MXS crystal shows a 32.7KHz wave on one side (as if half-wave rectified) and nothing on the other pin.
I changed it with a different one and it resonates nicely now on one side, with 900mVpp. The other side still appears like a half-wave rectified sine.

However, this still does not change anything, the LCD is still gray after booting.

As indicated in previous posts, I checked the SPI connection between the MXS and the MSP. I see data, clock and CS on all of them, with nice clean transitions. Data is being exchanged every time the ON button is pressed. The MXS also responds something when turning on and before powering off. If the power button is pressed for 5s continuously it reboots.

Speaking of booting, I also sniffed J5, a serial interface. Immediately after power-on, I get a "+" character, and right before gray-screening I get "Entry point: 0x00060040, address range: 0x00060000-0x003bef68" followed by a carriage return and a line feed. This looks like the output of a healthy meter (seen on one post above). This indicates that it can communicate with the flash memory, since MXS is only a processor, taking its program from the flash chip.

I started to focus on the MSP not enabling the 5V regulator. The scope shows that it does enable it, immediately after power-up. It pulls it down for 20ms and than it disables it again. The regulator appears to be working, as it outputs 5V. The reference is also ok, providing 2.5V at the MSP ADC reference input (for those 20ms).

I also noticed that the IR led does not blink to detect the probe connection. The driving transistor measures ok, the led lights up on the camera and the trace to the MSP is not interrupted (the pins are all well soldered too).

And here is where I got stuck.
I only have two (rather cold) leads: a faulty solder joint or via in the LCD data bus, since pins 15 and 17 are always 0v and both go to the MXS (but why does the start-up logo display correctly ?) and the weird driving signal for the MXS crystal (but MXS boots and displays proper message on the serial interface).

None of them appear connected to disabling the analog 5V rail.
Sorry for the long bed-rime story...

Any ideas on what else can I check?

Thanks,
MihaiV
MihaiV:
Here come the rest of the photos. This is the one with the gray screen.
MihaiV:
Immediately after removing the power, a single line briefly remains on the display. It is interesting that the conductive line from "beyond" the pixel array is also showing in black (at the edges). During "normal" operation is is not visible though.

The console output at booting is in the second attachment.
I also tried to send Ctlr-C during booting, but that simply hangs the power led in the on state and does nothing else.
YetAnotherTechie:
The line on the lcd doesn't mean that it's bad, it just means that it was an uncontrolled shutdown, i.e. the lcd drivers were not turned off in software before power went unregulated.
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