I have an old Mac Tools ET955 multimeter. It is also identical to a unit provided by Matco. The circuit board has the inscription 'Actron 400-1486' on the solder side. The problem is it constantly displays the count of '23' or '2.3' or '.23' with nothing connected, depending on the range selector. A 9-volt battery displays '+14v' or '-24v' depending on polarity. Adjusting the pots has no effect. I removed the MM5601BN quad 2-input NOR IC and the 7555 timer and the display reverted to all zeroes. So I assume either the 7555 timer chip or the 5601 chip is bad - not sure.
Anyway, does anyone have any suggestions on what could be the problem and where I could get a schematic and repair manual for the unit. I assume it is American made.
Thanks.
Anyway, does anyone have any suggestions on what could be the problem and where I could get a schematic and repair manual for the unit. I assume it is American made.
Thanks.
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Mac Tools Et 955 Manual Download
Oct 10, 2013 I have an old Mac Tools ET955 multimeter. It is also identical to a unit provided by Matco. The circuit board has the inscription 'Actron 400-1486' on the solder side. The problem is it constantly displays the count of '23' or '2.3' or '.23' with nothing connected, depending on the range selector.