| Electronics > Repair |
| Reverse engineer Dallas DS1742W? |
| (1/15) > >> |
| perdrix:
Did anyone ever strip one of these down completely to determine exactly what's inside them? Naturally there's a 2kx8 SRAM, a supervisory IC (what is it?) and a crystal ... The question is what else? Surely these can't be "rocket science" to reverse engineer with a replaceable battery? David |
| james_s:
We know exactly what's inside these, the PowerCap version is not potted. There is an off the shelf SRAM, a battery, a 32kHz crystal, and a Dallas ASIC which is a RTC and battery backup controller. Due to the custom chip it doesn't really help you to know what's in there although you can cut the old battery out and solder in a new one. While the DS1742W is discontinued, the DS1744WP is in active production and I made an adapter using those to replace the DS1742W in Tek TDS3000 scopes. You can build one yourself if you like, aside from mechanical fitment constraints it will work in any application designed for the DS1742W, and the PowerCap package it uses has a replaceable battery. https://github.com/james10952001/DS1744WP-to-DS1742W-adapter |
| james_s:
The DS1386 is the big brother to the DS1742 and is very similar inside. I do not currently have images of the DS1742W but I do have an intact dead one here kindly donated by another member so I will get that done eventually. |
| perdrix:
Are you *sure* that it's a non-standard ASIC acting as the RTC and controller. I was hoping it might be a DS1315 Phantom Time Chip which is an off the shelf part (assuming they are still available) which is what was used in the DS1244. Are you sure it doesn't use one of those? Yes I was aware of the DS1744WP but by the time you've bought that and the PowerCap it's quite a bit of cash! Does anyone have a dead DS1742 I can rip apart? David |
| james_s:
Yes I'm sure it's not a DS1315 or any other kind of phantom time chip, the RTC functions are not "phantom", they're fixed addresses overlapping the top handful of bytes of the RAM. You don't have to use any fancy tricks to access them like you do with the phantom RTCs, the enable to the RAM is passed through the RTC chip and when you access the RTC addresses it enables those and doesn't assert the chip enable to the SRAM. You don't need to rip one apart to see this, just look at one of the PowerCap versions as they're a bare PCB with the chips right out in the open, or compare the datasheets and it's obvious the RTC registers are different. Dallas makes or made a whole handful of RTC chips, some of the ones they offer integrated into potted modules are available separately, others are not. Yes the DS1744WP is not trivially cheap, however when it's the part needed to get a $500-$1500+ scope or other valuable instrument back up and running it seems pretty cheap to me. Also once you've installed that you can easily replace the battery the next time it goes dead without having to do any surgery. The low budget alternative is to cut out the old battery and solder in a new one, it's right under the top of the potted module, if you cut the plastic lid off one side you can often see the battery peeking through a thin layer of epoxy. It's a standard BR1632 lithium button cell. |
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