MJLorton Solar Power and Electronic Measurement Equipment Forum
Older Technology => Older Technology => Topic started by: Mr Eastwood on April 27, 2016, 04:02:26 AM
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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/ (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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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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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?
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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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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.
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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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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.
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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.
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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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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?
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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.