Author Topic: Sun Blizzard A/C Machine QTech II - troubleshooting board and cpu  (Read 478 times)

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Offline DK87

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  • Country: de
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... ???
All other lines are DEAD  :--

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 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:!AjDFITipILdAyUSNivWeN7ldm3ej

Thank you!

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