Author Topic: Cropico ESC1 Electronic Standard Cell  (Read 3684 times)

Mr Eastwood

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Cropico ESC1 Electronic Standard Cell
« on: April 27, 2016, 04:02:26 AM »
Hi,   this is something I bought on ebay for 5 odd, basically just wanted see if it still worked, unfortunately it was dead;  a similar one has been taken apart already on the eevblog, but I thought the verification record was quite interesting so I thought post a pic up for anyone to see, if they were interested.

The eevblog link
 http://www.eevblog.com/forum/metrology/cropico-esc1-electronic-standard-cell-a-look-inside/


I found a duff cap which I will try and replace see if it works again but I rather stupidly took out the Transistors to test them and didn't mark which one went where;  one is easy because it's a pnp, the other 2 are npn;  can anyone (Sean?) verify where the other 2 go ?  lol
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Mr Eastwood

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #1 on: April 27, 2016, 04:13:46 AM »
ah;  i just looked over the eevblog pictures and it does show a side pic of the board in question;  and I think it's (from top to bottom)  BFY51, BC178b (pnp) and BC108b - i'll check that out tonight.
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SeanB

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #2 on: April 27, 2016, 07:05:38 AM »
That thing must have kept a battery company in the black just from the batteries for one unit alone in a year. So which blue tantalum let out the smoke?

Mr Eastwood

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #3 on: April 27, 2016, 07:31:34 AM »
This one is shorted;  I think some of the others are iffy - i'll have to run over those again with my cap meter.
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SeanB

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #4 on: April 27, 2016, 09:35:58 AM »
10uF 35V is about the most common value blue tantalum, aside from 22uF 16V ones. At least that is the size I most commonly see in equipment.

Mr Eastwood

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #5 on: April 27, 2016, 12:37:37 PM »
I replaced the cap;  added the 3 transistors back in and fired it up and it works! it draws ~16mA@27v  not amps like before :-)

After leaving both my 7150 on and the standard cell I heated the room to ~20-ish and measured 0.999815v,  my other DMMs measured 0.9989v and 0.9986v (not sure i trust these).  So then I hooked up my Time DV Voltage Calibrator and set to 1.0000 v and I got 0.999815v which was exactly the same as the standard cell, lol



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SeanB

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #6 on: April 27, 2016, 01:11:43 PM »
Nice, a new addition to your standards collection. Should still be useful as it has had a good few decades to drift to a stable point.

Mr Eastwood

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #7 on: April 27, 2016, 05:12:54 PM »
yes it is, i'm really pleased with it :-)   what amazes me is all the trouble they went to put these together.

I just tried the 7150 from cold and it started high then was very close to the standard cell around 2-3 mins in after startup then dropped down;  probably would have dropped off to the low reading I posted if i'd left it on for a bit.   The 7150 had a fix prior to the cal a few years back so not sure if that had any bearing on it reading off so much.




 
« Last Edit: April 28, 2016, 12:48:50 PM by Mr Eastwood »
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Mr Eastwood

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #8 on: May 08, 2016, 12:35:32 PM »
Yesterday I took out all the C cell battery holders and cleaned the mess underneath from the previous owners set of leaky batteries;  then I got 2 x AA battery holders that holds 8 batteries each (24 volts)  and hot "snotted" those in place;  I previously tweaked the pot on the main PCB of the unit using my power supply so the low battery light comes on at around ~21 volts as per the manual instructions.

The reason for all the 18 C cells was to give the unit a larger thermal mass so once it was at that special verification temp of 20c +-0.5 it would stay fairly constant;  but as I don't or ever will have anything that will come close to measuring this -  it's just not worth me replacing the original C holders and batteries.
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SeanB

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #9 on: May 08, 2016, 12:38:59 PM »
Funny thing is that a modern alkaline AA cell has roughly the same capacity as a regular C cell did years ago, so you have not really lost any run time. Going to put a protective plastic sleeve around those holders just in case?

Mr Eastwood

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Re: Cropico ESC1 Electronic Standard Cell
« Reply #10 on: May 08, 2016, 12:43:52 PM »
Funny thing is that a modern alkaline AA cell has roughly the same capacity as a regular C cell did years ago, so you have not really lost any run time. Going to put a protective plastic sleeve around those holders just in case?

I wasn't, but now you've just scared me (lol) I might well do that as it's a good idea.
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