Electronics > Repair
Reverse engineer Dallas DS1742W?
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james_s:
It's always interesting to open up a potted assembly to see inside. We already know exactly what's in there though, the PowerCap versions of the Dallas ICs are made with the same parts and are not potted. In the case of the DS1744 there's a SRAM, a Dallas RTC ASIC, a 32kHz crystal and a coin cell.  I don't have a PowerCap version of the DS1742 but the potted one looks like it has only one IC in it. I'll xray the one I have when I have a chance, using a small focal spot tube and mammography film produces images sharp enough to see the bonding wires in SC70 packages. Unfortunately the limiting factor is scanning the film into digital format.
zebity:
Hi James_s & Co,

I have taken off the top layer of original DS1742W-120 from one of my SGI machines.

James is right the construction is substantially different, with harder further epoxy casing which is stamped with an Arrow and nomenclature (in reverse from casting) "M12C, 131, B".

It is going to take a bit more digging to see the internals of this one...

Here is picture of initial opening:



EDIT: And now with top epoxy mostly removed (showing oscillator and battery):



Cheers from Oz,

zebity/jwhat/John.
james_s:
Try heating the epoxy if you haven't already. I de-potted a number of HeNe laser power bricks using a heat gun and various scraping implements. Do it outside though or with plenty of ventilation because it stinks. I found that many potting compounds that are rock hard at room temperature become quite pliable when hot.
zebity:
Hi James_s & others,

yes thanks for tip on head gun, I used this for the second fake DS1742W-120+ de-pot and this one on DS1742W-120.

Here is insides view:



I cannot read the stamp on the contained IC as it is too faint.

It looks like 2 x 16 contact surface mount.

24 (exposed) + 2 (oscillator) + 2 (power) = 28 so 4 other contacts.

I am sure I read somewhere what the internal IC chip was and it was also no longer available from Maxim like the DS1742W.

I will so some further research on this.

Cheers from Oz,


zebity/jwhat/John.
james_s:
Not surprisingly, it looks exactly like the xray I took of one.

In many cases the exact IC used in these was never sold separately, I did manage to get some for the larger part used in the TDS700 series scopes from a China seller but I have no idea where they got them.

To read the number, try wiping it with a damp cloth, sometimes that helps. Also try shining light from various angles, it looks almost readable in the photo.
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