Finding TTL voltages in a mostly unknown circuit/microcontroller

[than3]

I've done some minor digital electronics repair over the last few decades, mostly just replacing blown caps or reflashing/replacing an SPI package; but overall I'm about 50/50 when it comes to not destroying whatever it is I'm working on. Not even what I'd consider hobby level, as its more of a last ditch attempt at salvage.

I'm wondering if there is a better way to go about identifying the voltage levels of circuits in a safe non-destructive way when the chip is not known, or identifiable.

More than a few times I've accidentally shorted/destroyed the packages using my test probes from my oscilloscope, where the circuit turned out to be 1v8 instead 3v3, or 0v8->2v7; or a weird switch between the two with another in-line microprocessor (Thinkpad mainboard W series, for EC-firmware).

Any recommendations on avoiding this inadvertent damage, especially in the case where there don't appear to be any protection resistors on the associated ground pin of the package?

 

[silentbogo]

Any recommendations on avoiding this inadvertent damage, especially in the case where there don't appear to be any protection resistors on the associated ground pin of the package?

There is no magic solution. Your only options are: google, schematics(if available), and a multimeter. It all boils down to looking for datasheets, reading datasheets, and making logical conclusions based on datasheets or your previous experiences.
Also, a rule of thumb: don't connect power to anything if you don't know whether it works or if you don't know proper VCC.
Another thing to note in regards to SPI flash: if you are using a cheap programmer, like CH341a or something, then you may want to invest at least in a proper 1.8v SOIC adapter with TTL level shifter. But I'd rather get something better/newer like TL866II or T56. The problem with CH341a, is that while it can do 3.3V on VCC and while most 1.8V SPI flash can survive 3.3V TTL levels, that stupid little thing still outputs 5V on data pins(even on newer revisions they didn't fix it). For 1.8V flash chips it's a death sentence.

 

[than3]

There is no magic solution. Your only options are: google, schematics(if available), and a multimeter. It all boils down to looking for datasheets, reading datasheets, and making logical conclusions based on datasheets or your previous experiences.
Also, a rule of thumb: don't connect power to anything if you don't know whether it works or if you don't know proper VCC.
Another thing to note in regards to SPI flash: if you are using a cheap programmer, like CH341a or something, then you may want to invest at least in a proper 1.8v SOIC adapter with TTL level shifter. But I'd rather get something better/newer like TL866II or T56. The problem with CH341a, is that while it can do 3.3V on VCC and while most 1.8V SPI flash can survive 3.3V TTL levels, that stupid little thing still outputs 5V on data pins(even on newer revisions they didn't fix it). For 1.8V flash chips it's a death sentence.

Thanks for the response.

I have a CH341a, and I think the issue you mentioned may have been the culprit a number of times after fixing power on a dead laptop (and flashing the SPI).
I'll take a look at the TL866II or T56.

With regards to TTL level shifters, given my limited knowledge of electronics I've had some difficulty determining if these adapters were safe. I've tried a few but when hooked up to an oscilloscope it didn't have a clean signal. Like anything off amazon these days what I've tested has been hit/miss, and I was trying to work through building one but as I mentioned I've only got a limited/passing knowledge of electronics (from working with ARRL material).