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missing op-amp chip in kill-a-watt?

by mrtz on Sat May 09, 2009 6:06 pm

To my surprise, when I opened my kill-a-watt (P4400), it looks like a different design from what is described in the tweet-a-watt guide. It does not seem to have any DIP chip on the PCBs. Did they stop using an op-amp in their design? Anybody else seen this. I bought my kill-a-watt on amazon.com about 1 month ago. I've attached a photo of this. On looking closer, I see that the transistors used are: CJ 78L05 near the large 100uF capacitor and the other 3 are all ST 2N3904.

I ordered a tweet-a-watt kit from adafruit and hooked up everything from as per the online guide, but I'm not sure how to proceed now at the final hookup step. Any ideas? Thanks.
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Re: missing op-amp chip in kill-a-watt?

by adafruit on Sat May 09, 2009 10:22 pm

can you post a photo?
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Re: missing op-amp chip in kill-a-watt?

by mrtz on Sun May 10, 2009 9:02 pm

attaching the photo
Attachments
P1000750.JPG
kill-a-watt without op-amp
P1000750.JPG (330.03 KiB) Viewed 10807 times
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Re: missing op-amp chip in kill-a-watt?

by The_Don125 on Sun May 10, 2009 9:15 pm

Looks like the Kill-A-Watt got an update. Reading the product numbers on the main board, the one pictured in the Kill-A-Watt build guide has a product number of 65120001 revision C, while yours is P/N 65120002 revision A.
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Re: missing op-amp chip in kill-a-watt?

by adafruit on Mon May 11, 2009 10:53 am

please take photos of the other sides of the PCBs as well! i need to see what SMT chips are on there
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Re: missing op-amp chip in kill-a-watt?

by mrtz on Mon May 11, 2009 12:25 pm

I'll take some more photos and post them later this evening
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Re: missing op-amp chip in kill-a-watt?

by chickensandwich on Mon May 11, 2009 1:41 pm

The op-amp is on the other side of the pcb, located directly behind the lcd.
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Re: missing op-amp chip in kill-a-watt?

by mrtz on Tue May 12, 2009 8:38 am

The markings on on the smaller SMT chip was covered with a black marker or something. I scraped the top gently with a penknife and tried my best to zoom into it - some characters are not visible, but hopefully someone can identify the chip. The larger chip is "2902 JRC A8058B".
Attachments
P1000759.JPG
zoom into smaller chip with barely legible markings
P1000759.JPG (53.39 KiB) Viewed 10743 times
P1000755-1.JPG
zoom into larger chip
P1000755-1.JPG (69.23 KiB) Viewed 10744 times
P1000755.JPG
back view on LCD side - the smaller chip was blacked out
P1000755.JPG (441 KiB) Viewed 10750 times
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Re: missing op-amp chip in kill-a-watt?

by adafruit on Tue May 12, 2009 12:55 pm

fancy! yeah, just solder the ribbon cable to the SOIC op amp chip's pins. the pinout is the same. the indented dot is pin #1
it should work the same way, i doubt they changed the functionality
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Re: missing op-amp chip in kill-a-watt?

by mrtz on Tue May 12, 2009 2:21 pm

ladyada wrote:fancy! yeah, just solder the ribbon cable to the SOIC op amp chip's pins. the pinout is the same. the indented dot is pin #1
it should work the same way, i doubt they changed the functionality


Are you saying that the A8058B chip in the new design is the equivalent op-amp of the LM2902N in the old design (described in the tweet-a-watt instructions)?
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Re: missing op-amp chip in kill-a-watt?

by adafruit on Tue May 12, 2009 3:23 pm

A8058B is the date code
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Re: missing op-amp chip in kill-a-watt?

by mrtz on Wed May 13, 2009 12:11 am

I was confused. Thanks for your help - I'll try it out.
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Re: missing op-amp chip in kill-a-watt?

by mrtz on Wed May 20, 2009 1:05 am

Just as an update: I was able to solder up the surface mounted op-amp as per older instructions - ie same pin configurations as ladyada mentioned. Of course it was as little harder due to the smaller pins. But eventually, I think I got it right. To get the wires out from the LCD side, I made two little notches on the upper left and upper right of the PCB from which I let the soldered wires out to the other side. I made the notches to be careful, since I found it hard to get the wires out to the other side since the PCB is flush with the plastic case, and I felt that the wires may break internally or pull the delicate soldering off the op-amp.

Also, I have been able to successfully run the wattcher script too and I get power data as expected, so all is fine. I can confirm that the new surface mounted type op-amp in the new Kill-a-watt design is still usable with the standard Tweet-a-watt design and guidelines. I'll post some more photos of the hookup later.
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Re: missing op-amp chip in kill-a-watt?

by adafruit on Wed May 20, 2009 9:53 am

awesome! thanks for offering to take a photo. do you mind if i add this to the tweet-a-watt docs? i have 5 kaw's and all of them are the same style :?
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Re: missing op-amp chip in kill-a-watt?

by mrtz on Wed May 20, 2009 1:27 pm

Sure, please go ahead. I'll post more pictures by the weekend to go with my description.
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