Hi All,

Back again with another jiggered bit of agriculture.

Tha dash on my JCB fastrac has been intermittently failing now permanently blank.





I've spent quite a few hours prodding it with a multi meter and scope.

Findings are,
The main processor is a MC68HC11F1CFN3, according to the datasheet is a rom less processor so am I right to assume it's running the program from the AM29FD10B flash next to it?

I've scoped the databus and it looks busy.

The processor is powered and oscillating.

Also on the board are 7 x 74hc165 these handle most of the inputs into to dash that are either 1 or 0.

These should be clocked by pin32 (SCK) of the processor ,also on this clock branch are the clock input for the display drivers (MSM5265) and RTC ds1302.

There was no signal on this clock line (0v) so I cut the track from the processor to see if it was trying to clock it.

Scoping the pin shows this.


This is with nothing connected to that pin.
Am I safe to assume that pin SCK has expired? Or should there be a pull up somewhere which I've disconnected and it's likely to be a chip on the spi failed.

If I buy a processor will in run from the flash or do they have to be programmed first? I assume it's running in expanded mode.

Sorry for long winded post.

Thanks Geoff

 

Just edited it, I'd missed a C out the processor name!

 

Just been reading up a bit more on these micro controllers, I'm still a bit unsure. If I buy a new one and fit should it run from the eprom on the board or will it need configuration?

Read a app note, you can read and write to the chip using the tx and Rx pins but if it's write protected it wipes the rest of the addresses?
It's not wholly clear if these addresses are used at all in expanded mode?

I suppose I have not too much to lose.....

 

An update to this, I got a new processor today and soldered it in.
The data bus is nice and busy so I think it's running?
Still not working though, but while I had the scope on I prodded the crystal for the rtcc , it's dead with no oscillation, I really should have checked this before but which is likely to be at fault? The xtal or the chip?

Cheers Geoff

 

Just changed the crystal on the ds1305 chip as I couldn't find a nice looking signal, still can't find a nice signal, I'm expecting it to be similar to what I find on the micro crystal just slower?

Is there any reason it would have a tiny amplitude I can't see? Or am I instead looking to change the 1305?

Cheers