Electronics > Repair
Reverse engineer Dallas DS1742W?
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zebity:
Hi James_s,

thanks for feedback.

Yes I am aware that this might be a "fake" or the other alternative is that it is faulty.

It was a DS1742W-120+ variation which appear to be the ones which are the potential "fakes".

These have the battery and PCB on the bottom and not the top.

Is your X-ray of DS1742W-120 or DS1742W-120+ and is there any known difference in these variations ?

The spec sheet just indicate that the -120+ is lead free.

I have known good DS1742W-120 variations which are from my SGI machines, but have deliberately held back from opening these up until I complete some further testing and validation with EEPROM programmer I have been using.

I currently have two known good spares.
In playing with the "fakes" I am now pretty comfortable that I will be able to open up "real" variation with confidence that I will not damage it.


Cheers from Oz,


zebity/jwhat/John.
Rasz:

--- Quote from: zebity on October 27, 2020, 12:21:26 am ---Full details of drilling/heating and cutting: https://tips.graphica.com.au/sgi-nvram.

--- End quote ---

>Mixed Content: The page at '<URL>' was loaded over HTTPS, but requested an insecure image '<URL>'. This request has been blocked; the content must be served over HTTPS.
james_s:

--- Quote from: zebity on October 27, 2020, 04:04:12 am ---Hi James_s,

thanks for feedback.

Yes I am aware that this might be a "fake" or the other alternative is that it is faulty.

It was a DS1742W-120+ variation which appear to be the ones which are the potential "fakes".

These have the battery and PCB on the bottom and not the top.

Is your X-ray of DS1742W-120 or DS1742W-120+ and is there any known difference in these variations ?

The spec sheet just indicate that the -120+ is lead free.

I have known good DS1742W-120 variations which are from my SGI machines, but have deliberately held back from opening these up until I complete some further testing and validation with EEPROM programmer I have been using.

I currently have two known good spares.
In playing with the "fakes" I am now pretty comfortable that I will be able to open up "real" variation with confidence that I will not damage it.


Cheers from Oz,


zebity/jwhat/John.

--- End quote ---

Looking again, your chip is 100% a fake. It has the same weird texture and faint blurry printing as the fakes I got a few years ago, and the internal layout is completely different. Mine is a DS1742W-150 out of a Tek TDS3000 scope but there is no visible difference inside parts of different speeds. I have xrayed 5 or 6 genuine DSxxxx parts and a handful of fakes and all of the genuine parts have a similar style. Fine traces, small vias, surface mount packages, very tidy assembly. The fakes are different, look at the PCB you extracted, big fat traces, huge vias, sloppy soldering, DIP package inside. Measure the external dimensions, the fakes are larger than the genuine parts.

The DS1742 went out of production several years ago so if you buy one with a current date code it is fake. If you buy one from China it is either fake or an old used part. Ebay is full of fake Dallas chips, you can tell immediately by the prices. Don't be scammed, the fake parts don't work.
Rasz:

--- Quote from: james_s on October 27, 2020, 06:38:05 am ---Don't be scammed, the fake parts don't work.

--- End quote ---


dont work in what specific way? they sure keep stuff in SRAM and return time
james_s:

--- Quote from: Rasz on October 27, 2020, 08:36:05 am ---dont work in what specific way? they sure keep stuff in SRAM and return time

--- End quote ---

I bought about 10 different ones before I knew better. Out of all those I had two that worked, both were genuine parts that had clearly been sanded, blacktopped and printed with new date codes, they even came pre-loaded with data.

The others were all defective in various ways, most had different problems. Going from memory:
- Chip was readable but writes had no effect, could not store data on it or set the time.
- Completely dead, reads resulted in garbage.
- Seemed to work ok on programmer but did not function properly in scope.
- Read and write worked, but conents lost when power removed (defective battery)

Seems like there was some other symptom but I don't recall what it was. Incidentally I cut open most of the defective ones some time later and all of the batteries were below 1V by then, none lasted more than a year or so.

Then there is the fact that they are counterfeit parts created as a deliberate attempt to scam buyers. I would be willing to buy a Won Hung Lo branded "WHL1742" or whatever sold as a compatible replacement for a DS1742 provided that it works, there is clearly a market for these so it surprises me that no Chinese companies are doing it. But don't try to sell me a counterfeit Dallas branded part, that is cheating.
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