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Bricked Fluke 177

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andyB2022:
How can I check that? I don't have any datasheet on the pins of the ASIC... I've probed something yesterday around some vias for the ASIC but found nothing....

AVGresponding:
Unfortunately the only way is to trace it out the hard way... as you've found, with it being a multi-layer board it's a difficult proposition.

The 8x series uses the same ADC, its connections to the main ASIC are:

Pin 11 CS (ADCS*) --> ASIC ADCS*

Pin 12 SDO (D-OUT) --> 49k9 resistor --> ASIC D-IN

Pin 13 SCK (ADSCK) --> ASIC ADSCK

Obviously CS should be over rather than under-scored, but that's not so easy to do here...
The resistor in the data line will make it harder but not impossible to identify the pin on the ASIC.

Now, on the 8x series, the main ASIC is the main signal processor and also the display driver; I don't know if this is the case with the 17x series. If they are separate, the symptoms could indicate a dead MSP ASIC, with the display driver outputting those dashes as a kind of default in the absence of instructions.

Before any of that though, can we recap on some earlier measurements? If the ADC is meant to be getting 3.3V and it's getting 5V that's not good. In the 8x series the ADC is supplied with +/- 2.5V, the REF and VIN are connected to GND. It would be useful to know which is correct for your case.

AVGresponding:

--- Quote from: andyB2022 on July 16, 2022, 11:25:00 am ---Here are the DSO captures for :LTC2435

As far as I know about SPI, SCK signal doesn't look good...(pin 13)

--- End quote ---

It's hard to say whether any of the overshoot might be artifacts of the measuring setup. Here's the excerpt from the 8x service manual on the ADC operation:

Analog to Digital Converter
U3 is a 20-bit Σ∆ analog-to-digital converter (ADC). C21 & C22 are power-supply
bypass capacitors. The DC signal at FE_O (U1 pin 19) provides the signal input for U3.
The reference for conversion is supplied by U8 as described in 1.3 to the REF and VIN*
(compliment of VIN) inputs. Since REF* (compliment of REF) is tied to -2.5 V and both
pairs of inputs to U3 are handled differentially, the dynamic range of the VIN is ±1.25 V
around COMMOM. The microprocessor U2 uses three digital lines to communicate with
U3. U3 signals the microprocessor U2 that a conversion is completed by pulling the SDO
signal line to logic low (-2.5 V), which is coupled through current limiting resistor R31
to DOUT. When U2 is ready for the reading, it pulls ADCS* of U3 to a logic low and
clocks the data serially out of SDO with the signal ADSCK applied to SCK. Connecting
F0 of U3 to -2.5 V sets the internal clock so that the normal mode rejection ratio
(NMRR) of the digital filter will provide adequate rejection of both 50 Hz and 60 Hz.

I've left the Fluke typos intact...

andyB2022:

--- Quote from: AVGresponding on July 17, 2022, 10:29:23 am ---Before any of that though, can we recap on some earlier measurements? If the ADC is meant to be getting 3.3V and it's getting 5V that's not good. In the 8x series the ADC is supplied with +/- 2.5V, the REF and VIN are connected to GND. It would be useful to know which is correct for your case.

--- End quote ---

REF- is the only pin tied to GND.
VCC pin has 5V on it (datasheet says between -0.3V to 7V)
REF+  2.5V
IN+  2.5V
IN-  2.5V

All display related traces come exclusively from the microcontroller, most of them are on the top layer. So the ASIC has nothing to do with dispaly (I guess).

andyB2022:
I've found a great offer for around 16$ shipped to my country (Romania, Europe) for the ADC and ASIC chips.
The question is, may it work with those things new? (I know meter will need recalibration).

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