Electronics > Repair
Reverse engineer Dallas DS1742W?
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sicco:
For the tds3000 scopes, I have an alternative in the making, partly inspired on james_s DS1744 patch piggy back board. My board has same DS1744W but plugs into the scope rear expansion connector for RS232, VGA, GPIB, Ethernet. My board will get you not just the RTC, but also isolated RS232 DB9, isolated micro USB serial port, Ethernet RJ-45, and allows an ESP32 DevKit4 to be added for those that want the WiFi web server from Russia discussed in other thread on tds3k elsewhere on eevblog. No VGA or GPIB though.

For this dead DS1742W workaround, the old DS1742W on the main board needs to be disabled - as in cut its pin 24 VDD or have its /CS input pin forced always high.

I’ll make a few more quite likely.

Expecting the JLCPCB delivered in a week or so - so fingers crossed.
james_s:
I wonder what IC that ebay replacement is using? My solution is cheaper if you build it yourself, but I'd have to charge at least as much if I were building them for other people for it to be worth it, the parts cost around $50 IIRC.
helius:
If the equivalent battery-less Dallas clock-memory chips are not available, I think you would need to use something that can be programmed somehow (to match register functions and access time). Low-power CPLD or Silego glue, maybe even PSOC?
zebity:
Hi EEVbloggers,

I have pulled apart the DS1742W-120+, here is summary:

Draft Pin Details:

Pin 1 - Notched - Straight Through (A7)
Pin 2 - Notched - Straight Through (A6)
Pin 3 - Notched - Straight Through (A5)
Pin 4 - Notched - Straight Through (A4)
Pin 5 - Notched - Straight Through (A3)
Pin 6 - Notched - Straight Through (A2)
Pin 7 - Notched - Straight Through (A1)
Pin 8 - Notched - Straight Through (A0)
Pin 9 - Top Side R1, Under Side T1 (DQ)
Pin 10 - Top Side R5, Under Side T2 (DQ)
Pin 11 - Top Side R6, Under Side T3 (DQ)
Pin 12 - Notched - Ground Layer (Battery -Neg)
Pin 13 - Top Side R7, Under Side T6 (DQ)
Pin 14 - Top Side R8, Under Side T5 (DQ)
Pin 15 - Top Side R9, Under Side T5 (DQ)
Pin 16 - Top Side R10, Under Side T9 (DQ)
Pin 17 - Top Side R11, Under Side T8 (DQ)
Pin 18 - Notched - Straight Through (^CE)
Pin 19 - Notched - Straight Through (A10)
Pin 20 - Notched - Straight Through (^OE)
Pin 21 - Notched - Straight Through (^WE)
Pin 22 - Notched - Straight Through (A9)
Pin 23 - Notched - Straight Through (A8)
Pin 24 - Top Side C2 (VCC), Under Side C3 (10A45)

Draft Components

Capacitors x 3 (10A45)
Resistor x 8 (102) - 1 per Data Line
Voltage Regulator IC 6 PIN 10A45
Oscillator Crystal (Pin 1/24 Notch)
Battery Cell  - 3V CR1225 (+Pos Pin 12/13 Notch, -Neg Pin 12)

Here are pictures of PCB board that is encased in epoxy and sits underneath the main IC:





And here is carefully cut chip with battery extracted:





Full details of drilling/heating and cutting: https://tips.graphica.com.au/sgi-nvram.

If someone else has nice pre-built replacement then I think I would just use that ... ;-)

Cheers from Oz,


zebity/jwhat/John
james_s:
That's not a genuine DS1742W, at least it's not like any genuine DSxxxx part I've seen. Where did you get it from? It looks like one of the Chinese clones (that don't work properly) that are all over ebay. Look at my xray a few posts above, the genuine part has a completely different layout.
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