No display on LCD

[Farah]

I'm repairing a Rig Flow Display. This device has 2 small LCDs, some LEDs and a large LCD shows graph. There is no display on a large LCD display. The other small LCDs and the LEDs are normal working. I replaced the LCD but the problem persisted. I replaced the CPU Board with a healthy CPU Board and the problem was solved. There is no short circuit on the faulty CPU Board. The CPU board equipped with these chips: ADM101E, ADuC845, LM234, LME1205DC, OP29G, REG102, SN74LV8151, and two smd code R1B and RCB by packing sot-25 (I didn't find the part number of these 2 code ). Please advise which chip is the problem?

[Swake]

What do you think yourself? What chip in your list might control an LCD? Eliminate those that are unlikely to control the LCD and you'll be very close. The fault might be in that chip that remains but that is not necessarily the case. In the event it is that chip you'll have to find some way to program it as there might be some code stored in it.

[ledtester]

What is a "Rig Flow Display"? It sounds like a specialized device so posting a picture of it would be helpful.

What kind of LCD display are we talking about? Post a pic of it. Showing the interface would be very helpful. If it is a certain kind of display it may just need a contrast adjustment.

What does the CPU board look like? What is the CPU on the "CPU board"? You mention a lot of chips on the board but none of them are a CPU or microprocessor.

Do you know that the new display actually works? You can test this by installing it into the working CPU board and seeing if it shows graphs.

The input to a LCD display is usually a set of digital signals. If you have an oscilloscope you can see if data is being sent to the display. We would need to know more about the display to advise further.

[Farah]

RD-G remote display is the industry standard for reliable, rugged presentation of critical information for directional drillers and MWD operators.

I attached the image of device and its CPU board.
As I see and trace the track on the board, the ADuC845 (MicroConverter Multichannel 24-/16-Bit ADCs with Embedded 62 kB Flash and Single-Cycle MCU) and SN74LV8151 (10-bit universal Schmitt-trigger buffer with 3-state outputs) connect to the 240*64 LCD (the LCD with backlight on and no display) connector. there is no short circuit on these chips or the other chips on the board.
At first I changed the 240*64 LCD with the new one, but the problem didn't solve. I changed the CPU with the CPU of Healthy device and the image of display appear and it shoes that the CPU board has problem.

[Swake]

Make sure power supplies are fine (up to the LCD; the MCU and the SN74LV8151). Do not assume these are ok because the rest of the circuit seems working. Check for correct voltage, stable and ripple (AC component).

With a multimeter in diode mode: check all pins, connections and tracks are fine between MCU and LCD connector, noting open; broken or damaged?

Use a scope to trace the signals between MCU and SN74 and the LCD.

If you don't have a scope but can solder: the SN74LV8151 is only a 1$ component. Swap it out, it is a cheap try.
Swapping out the MCU is somewhat more difficult as it will require you to program it.

Have you tried using the 'bad' CPU board with the other 'good' display and found the same issue?

[Farah]

Thanks a lot for your details. The OP295G and SN74LV8151 are the chips between MCU and LCD. By ohm and diode check the pins, I noticed differences between these components and the components of the healthy board. I changed the defected components and sent them to the customer for testing (I only had the device control board). I hope it works.