Avo EA113 DC current ranges fault fixed

[Phil G4SPZ]

Since repairing it a few years ago, I use my EA113 on a daily basis, but only rarely use the current ranges, so it was with some consternation that I found that all the DC current ranges had stopped working.

A quick test with a current limited source showed that the various range shunts R72 to R78 were all in circuit and working. A study of the circuit proved that resistor R61 (31.62k) and switch SB2 are the only components that could cause this fault. R61 is on the underside of the range board, and turned out to be blameless; the cause of the fault was a dirty sliding contact on SB2. A squirt of Servisol 10 restored the DC current ranges to normal operation.

Phil

[mole42uk]

Excellent, Phil. I have two of those, one works perfectly, the other has a faulty DC side. I’m hoping that the fix is just as straightforward - except, of course, that getting into the EA113 isn’t that simple!

[pmmunro]

Richard,

Do you have the service manual for the EA113? My reason for asking is that there is some dismantling information in it which could useful, although I have not had to work to it so far.

If you need the manual, send me a private message with an email address and I will get it to you.

PMM

[The Philpott]

If we were ever to create a generic fault-finding flow chart, 'Does it have moving parts?' would surely appear somewhere near the start.
Dave

[Phil G4SPZ]

So are you suggesting that things without moving parts, i.e. software-controlled devices, don’t go faulty?

[The Philpott]

-Those issues would just be further down the flow chart Phil !
(just before 'destroy memory and consign appliance to WEEE')

EA113 sounds useful with impedance 1meg/volt up to a max of 100meg- rather compact as well.

Dave

[Phil G4SPZ]

Originally Posted by The Philpott

EA113 sounds useful with impedance 1meg/volt up to a max of 100meg- rather compact as well.

Dave, as you may know, I have a great many test meters but the EA113 is the nearest thing to a universal multimeter I’ve ever used. Since I restored it, I have hardly used anything else.

[Radio Wrangler]

Just watch out, because they go loopy if there is RF power around. Otherwise, they are a brilliant little instrument. The other caution is that batteries last a very long time, so check for leaks and have a replacement plan even though they're running strongly.

David

[Alistair D]

Thinking about David's comment about the batteries lasting a long time gave me an idea. Use AAA batteries in adapters like this one.

https://www.amazon.co.uk/Battery-Adapter-Convert-Batteries-C...a+battery+adaptor%2Caps%2C66&sr=8-3

Depending on how well they are made they could reduce the damage when the batteries leak.

I am planning to buy some of these in the near future so I can run a battery instrument from a wall wart. The instrument does not have a DC input socket and I do not to drill the case. I will report back but do not hold your breath.

Al

[Phil G4SPZ]

Originally Posted by Alistair D

...I am planning to buy some of these in the near future so I can run a battery instrument from a wall wart. The instrument does not have a DC input socket and I do not to drill the case...

I can't quite see what you plan to achieve without some form of hole to take the cable from the wall wart...

David's suggestion about having a battery replacement plan is a good one. I'm currently buying alkaline AA cells from CPC Farnell which are dated "best before 2027" so if nothing else, a note of that date on a neat label tied onto the instrument handle acts as a timely reminder to replace them then, even if they haven't become discharged.

[mole42uk]

I must admit that I remove the batteries from mine when I put it back on the shelf. I, too, have a number of meters and the EA113 doesn't get used so often that I'd be happy leaving batteries in it - thank god for the Dzus fasteners!

[Radio Wrangler]

Don't use a wall wart. I think the batteries need to float with the input voltage and you may over-voltage the wart's isolation spec. This could be dangerous.

If I ever see any more of those Energizer 1.5v long life AA Lithium cells, I'll get a set for the 113.

David

[Station X]

Thread reopened at OP's request.

[Phil G4SPZ]

Thanks, Graham.

This annoying fault recurred a couple of times, and a squirt of Servisol cured it each time, but on the most recent occasion the fault returned and became permanent. The instrument still worked on volts and ohms ranges, but it niggled away at me and despite putting it off for some time, today I decided to grasp the nettle and have a proper look at switch contact SB2 which, looking at the meter from the back, is on the long six-pole 2-way slide switch on the underside of the range board. Switch SB is the AC-DC switch and is operated via a linkage by the two push buttons on the front panel.

Removing the range board isn’t quite as difficult as would first appear. Only half a dozen wires need to be disconnected, enabling the range board to be lifted carefully away and flipped over to gain access to the underneath, taking care to note the position of the double-sided range switch wafer, which rotates in the opposite direction to the range knob. The sliding portion of switch SB can then be removed by carefully prising upwards and twisting one of the two securing brackets, lifting the Paxolin switch wafer upwards and sliding it out. In the fourth photo you can see where the left-hand bracket has been released.

Once removed, it was obvious how dirty the fixed contacts were. I cleaned them thoroughly with IPA on a cotton bud. One of the moving contacts needed re-tensioning too. While I had the thing apart, I cleaned the accessible contacts on the range switch wafers as well. Before reassembling the meter I lashed-up the disconnected wires so that I could test the meter in its dismantled state, and it worked perfectly.

Hopefully it will continue to do so! A few photos show the relevant parts of the meter.

[Kevin Hoyland]

Morning Phil. outstanding work .

Kevin.

[Phil G4SPZ]

Thanks, Kevin! You’re too kind.

I have taken to checking the operation of the EA113’s current ranges on a daily basis. So far, so good… and here is one reason why I like this meter so much. Variable voltage bench PSU via a 100 ohm 1% resistor in series with meter. Switch EA113 to DC volts and set voltage from PSU to exactly 10.00 volts. Switch EA113 to DC current and it reads 100mA. Not 100.1 or 99.9, but exactly 100.0mA.

1 Megohm-per-volt on DC volts, and virtually no burden on DC current. Happy again!