Electronics > Repair
Fluke 289 not quite sorted.
MihaiV:
Hello again,
First with the (somewhat) good news: the LTC2415-1 (U10) ADC appears to be working. Attachment 1 shows the CS, SCK and SDO signals. The CS doesn't look too good with that falling edge. The data and the clock look good though.
The ADC is powered by the 5V rail, so the signals will have the same level. On the board, the CS and the SCK are connected directly to the MSP, but the SDO connects through a large resistor (measured ~50k in circuit). It seems that the ADC is operating alone right now, meaning that SCK is an output. AS the datasheet says, if SCK is HIGH or floating at power-up or during a High-to-Low transition, the converter enters SCK internal mode. Might be the reason for the dodgy CS signal too.
I believe it operates with SCK from the MSP in normal mode, because if I power it up with the scope probe attached to SCK it does not output anything, but if i power it without and attach it later it outputs clock and data.
Photos 2 and 3 show a weird data output (blue trace mostly High), and a zoom of the falling edge of CS.
And here is the bad news.
I just checked the SPI connection to U9 (SL10327) and nothing happens there, with or without external 5V. Checked absolutely every pin, powered up the meter on each one and I only see something on the power and the reference voltage.
Good news is that I found the IC on ebay.
Could anybody post a scope capture of what happens on the SPI bus of a functional unit ? Please?
Thanks,
MihaiV.
MihaiV:
Anyone?
booyeah:
From a good 289:
1. U10 (LTC2415), attachment 1 and 2 - CS bar, SCK, SDO. CS bar is directly connected to MSP 47 , but couldn't find where SCK and SDO went.
2. U9 (SL10327), attachment 3, 4, 5 - CS*(26) to msp (63), SCK (28) to msp (48), SDI (27) to msp (50).
Probe connections aren't the best, so some extra ringing.
MihaiV:
Hello Booyeah,
Thank you for taking the time to open your meter and investigate the signals!
My U9 appears very dead, so I ordered one from ebay(most likely removed from some other meter). There are some chances to be faulty too, but I'll take my chances for 5$.
Thanks,
MihaiV.
MihaiV:
Hello again,
The SL10327 arrived! The part appears new, in the tape, with no traces of removal from other equipment.
Swap it in and... nothing.
The problem is somewhere else.
Don't know where else to look at the moment...
Could it be a problem from the MXS or the RAM? Could the start-up logo be displayed from the ROM and when RAM operations start, everything goes wrong?
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