Hi there,
a few days ago I obtained an A/C servicing machine for cars/trucks.
It's in rather nice condition, but has one major issue: the LCD isn't showing anything. (see attachment)
So I began to remove the board along with the lcd to test it on the bench.
I took an visual inspection and I found an corroded ic (but seems to work just fine...I had probed it later)
Then I probed the connections comming out of the board to the LCD and there is no valid signal comming out of it:
frameground, ground, backlight positive and backlight ground are working
pin 6 (Read Select :->5V 140Khz square wave signal.... seems to be okay?
pin 11 (DATABUS 0) -> 3V 70 Khz sqare wave signal hmm...
![Huh? ???](https://www.eevblog.com/forum/Smileys/default/huh.gif)
All other lines are DEAD
![ThumbsDown :--](https://www.eevblog.com/forum/Smileys/default/icon_thumbsdown.gif)
So I think the problem is not the LCD.
I digged further and tried to get a connection to the LPC2148, but nothing works.
I probed UART0 Pins of cpu ->no valid signal
I probed UART1 Pins of cpu ->no valid signal
I tried usb-connection: error, windows says the device doesn't work.
Even if I pull the RESET pin low, and pin 0.14, so that the cpu will start the bootloader..no connections
I checked power supplies: 12V ok, 5V ok, 3.3 V ok.
I suspect the cpu hangs, has corrupted user software or is just faulty.
So, can you help me further?
Do I have missed something?
Btw I noticed:
There are HCT573 octale D-Type latches.
On a few latches the LE (LatchEnable) pin is on the 5V rail. Why?
I thought especially the latches which are connected to the lcd take the LE signal to send the databits simultaneouslyto to the lcd?
Unfortunately, I have no service manual or anything about that machine.
I contacted the manufacturer SUN aka Snap-On but still no answer.
Detailed and annotated pictures of the pcb are on my onedrive accout:
https://1drv.ms/f/s!AjDFITipILdAyUSNivWeN7ldm3ejThank you!