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    Eico 555 multimeter

    Well I got this old ancient Eico 555 meter and noticed that AC volts and ohms dont't work. Well, Eico used to be a kit provider, and this multimeter appears to have been assembled wrong - the battery pack appears to have no way to provide power into the resistance scales based on how the contacts on the waferboards are aligned and how the battery is fed in (I had to analyze it because I can't even tell which way is positive, as well as the fact if these are regular AA's or what?). And I don't know what's wrong with AC volts at all, it simply reads 0V.

    DCV and DCA seem to work just fine however.

    Anyone happen to have the schematic or assembly guide for the old beast (Google had some leads pointing to some public fileshare services that have since deleted the items)? I suppose the 565 is similar...

    #2
    Re: Eico 555 multimeter

    I sent mail off to Ken to his site, http://www.nostalgickitscentral.com/...eico_test.html and he restored the file that came up as a 404 yesterday. Thanks Ken!

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      #3
      Re: Eico 555 multimeter

      After some debug effort, found that:
      - The AC diode pack was shorted out. Don't know why.
      - The battery configuration was unexpected. The D-cell that is used for resistance was completely disconnected from the meter, didn't realize that it was a critical component.
      - There was one bad resistor, a 11.5 ohm 1% resistor that was showing up at 30K, causing resistance scales to be wrong.
      I swapped out the diodes (which happens to be a weird package, it was rectangular... perhaps it was a point contact diode?) with two cheap 1N34-clones, and substituted a 15 ohm 5% resistor for that broken resistor. Resistance is not very accurate but it now the meter generally works. I'll need to get a 11.5 ohm resistor...

      I was a bit surprised to see the AC on this meter moves the scale slower than DC/ohms/DC mA. I suspect it has a lot of parasitic capacitance, perhaps...

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        #4
        Re: Eico 555 multimeter

        Originally posted by eccerr0r View Post
        I'll need to get a 11.5 ohm resistor...
        Good job on the repair.

        11.5ohm resistor 1% available on digikey. Maybe wait to add a few things before ordering a single resistor?

        http://www.digikey.com/product-detai...5YCT-ND/596861
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          #5
          Re: Eico 555 multimeter

          I also have a Eico 555 which needed resistors. So I used series parallel combinations to get as close to the correct value as possible. I also replaced the diode bridge with two 1 amp diodes. My biggest problem is the battery pack which I have to replace. I am also going to try and replace the "D" battery with something smaller like a "AA" lithium battery. My biggest problem is the meter goes negative in the highest resistance range when the leads are shorted.

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            #6
            Re: Eico 555 multimeter

            Ah I ended up putting a 10 ohm and a 1.5 ohm resistor in series. Crappy accuracy but hell, it's pretty close.

            So your diode bridge also is broken? I went for the Germaniums because the voltage drop is lower, and hopefully would get more accurate readings (most passive meters at the time used germaniums as far as I know for this specific reason.)

            Now it's just the 10A range that doesn't do squat. I'm suspecting a bad or incorrect shunt resistor, but no way to test that.

            Gotta watch out, that D cell seems to drain 150mA or so when Rx1 is being used. As the holder was there, I just stuck in a cheap Manganese-Zinc battery (3 for $1 at Dollar Tree). The AA's I also used cheap Mn-Zn cells (8 for $1 at Dollar Tree). These crappy batteries should last virtually forever I'd think, I ended up using these because they are lighter than Alkalines and the meter is bulky enough itself.

            What do you mean it goes "negative"? The meter goes left when you short the leads? Or does it go right, and past 0? If it's the latter the "zero" potentiometer is used to fix that, which is a common operation on these analog meters. If it goes left, you'll need to check the wiring in the meter carefully...

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              #7
              Re: Eico 555 multimeter

              Well, sorry for the necro but I guess I wanted to post what I found.

              I used my bench PSU and passed 500mA through the 10A mode, and supposedly most of this current must go through the shunt. I hooked up my BKP2833 DMM to the two sides of the shunt. I measured 1.11 mV, luckily the BKP2833 had 10µV resolution (these are the days when I wish I had a 6 digit DMM, but only these days... most days I can get by with a 3½ digit just fine.)

              Well ohm's law says the shunt (and the rest of the meter) is 0.00222 ohms. The schematic says 0.025 ohms. I guess I found my problem, or perhaps someone modded this meter to deal with 100 amperes (!). The meter uses the old style probe jacks (where you can plug in either the probe end or the plug end of the probe wire) - which I seriously doubt can handle 100A, let alone 10A without significant loss. So I think I'll need to mod this back to 0.025 ohms, now whether I hack up a piece of resistance wire (like most other ammeters and as it is now, but with higher resistance) or find a 0.025 ohm resistor (or a combo of resistors)...

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                #8
                Re: Eico 555 multimeter

                Looks like I may have to get resistors. A 3W 0.025 ohm resistor from Mouser is $0.80.
                Or I could gang up 8 0.2 ohm resistors in parallel... which is unfortunately what I _do_ have in my parts box...

                But if I were to use a wire solution... I'm not sure nichrome wire is good as its temperature coefficient is high. Using copper wire is bad too... Currently the 10A jacks are 2" apart, and there's a straight piece of ~14 gauge wire that spans them. To get 25 milliohms worth of 22 gauge wire, I'd need...around 20 inches... And I'm not so sure that 22 gauge wire will pass 10 amperes for any extended amount of time, plus the fact that I'd need to coil it or something to get it to fit.

                Hmm... not sure what should have been there... or where I could get small quantities of low temperature coefficient resistance wire. I suppose it's hard to beat $0.80 ...

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                  #9
                  Re: Eico 555 multimeter

                  Well, I didn't feel like ordering just yet so I burned my 0.2 ohm resistors: connected 8 in parallel... and finally, the ammeter mode works fine now. Didn't check it against my DMMs but at least a couple of my other analog meters, it's within the ballpark. Now I can connect this in series with something and not worry about killing its battery after forgetting about it... like some of my other meters that kill its battery in just a few days.

                  Took a lot of solder to get those 8 resistors in parallel... I think they're 2W units too, so I guess as an aggregate whole, it now deals at least 15W.

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