Electronics > Repair

Fluke 8050A repair

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Here's some information on the Fluke's display, in case it's helpful to anyone...

* The LCD is controlled directly by the Fluke's processor, with the display data being latched with CMOS LCD drivers.
* The data bus consists of lines W, X, Y, Z; which is 23, 22, 21, 20 respectively.
* HV and DP lines are also part of the data.
* The BP signal is a 50Hz signal only used for refreshing the stock display.  Not needed for a custom display.
* Display data is latched with positive pulses on one of the five strobe lines (ST0 - ST4).
* Data is valid on both rising and falling edges of the strobe pulse.  (I grab the data on the rising edge.)
* Strobe 0 (ST0) latches data for U10, which handles the HV, BT, and REL indicators.
* A high on DP during ST0 indicates REL.
* The battery (BT) signal comes from a voltage dividier and PNP.  I don't use this, since my Fluke doesn't have those components.
* ST0 also latches data for U11, which handles the plus(+), minus(-), 1 (first digit), and the dB indicator.  W line is for minus(-), X is for plus(+), Y is for dB, and Z is for the "1".  Note that the plus(+) is actually two segments, so W *and* Y together turn on the plus.
* ST1 latches data for U12, which is the second digit (first whole 7-seg digit).
* ST2 latches data for U13, which is the third digit.
* ST3 latches data for U14, which is the fourth digit.
* ST4 latches data for U15, which is the fifth digit.
* U16 handles the decimals, and is latches by each of the strobes (ST1 - ST4).
* The display-only data can be taken from the display board ribbon, or rather the vias right next to it.
* Functions (Volts, Amps, Ohms...) are only available at the Fluke processor (which is why I made a carrier board).
* Ranges (2, 200, etc.) are also only available at the Fluke processor.
* The Vss pins of the chips runs at -5V.
* The Vdd pins of the chips runs at 0V.
* Display data is latched in sequence: ST0, ST1, etc.
* A strobe pulse is about 168us wide, though I observed some at 116us.  This isn't really useful anyway.
* There is about 216us between the falling edge of one strobe to the rising edge of the next.
* One cycle is pretty short, so it makes sense to grab all the data and then process it after ST4 is done.
* The whole cycle repeats about every 410ms.

Range switch logic (pins are of Fluke 40-pin processor):
Pin 3Pin 4Pin 5RangeRngARngBRngC200 ohm HHL2k ohm LHH20k ohm HLH200k ohm LLH2000k ohm HHH2M ohm LLL200 nS HLL2 mS LHL

Finally got my TFT display off the slow boat from China.  The 2.0" looks to be a good size for the Fluke 8050A's opening.  First step was to make sure the display works.  It does.  And it's a gorgeous display.  Gotta love the Arduino community to make these things easy.  Hardware SPI is the only way to go, as software SPI is painfully slow.  At least for the Arduino Uno.  I can run my PIC18F26K40 up to 64MHz.

Getting this setup, and porting my previous code to C, is going to take me a while...I was using a simple and uncommon compiler to get the OLED up and running that I'm sure nobody else would use.


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