1972 AVO 8 mk 5 in Amroh leather case.
This AVO8 is from 1972 and a mark V type. It still has all the features of the older models including a high voltage range. Besides tghat there is a button to reverse polarity. The cabinet is made out of platic and a lot less heavy compared to the older models. They made the model 8 from 1951 to 2008 in several subversions.
It has a very nice leather holster made by Amroh.
The Amroh case
Backplane and battery compartment
The special battery was included and still in good shape.
I tested all ranges and modes. Every was withing specs. The only problem was AC. Not a single response. Finding the fault was 5 minutes but fixing it a bit more. Two germanium diodes were killed in action. They were hard to replace due to the location.
Detail inside, the overload protection box
They are mounted on a smal pcb between pcb and the blue flex cable . You can only replace the board after you remove almost everything. So I cut the leads and soldered the new ones on the old wires. You need to be very carefull not to melt the plastic cable. After that I placed a resistor parallel to an other to calibrate it.
Repairing the ACV range
They have no adjustable trimpots for calibration. The instrument is within 1% on all modes The resistance range is scary acurate. My mkII is even better. The meter needs to be horizontal during use. The needle is wonderfull damped. I think this is the most usefull model. It is accurate, very well protected and can be used for high voltage but also for very low voltage and current. The resistance is rather low compared to a modern DMM. It is 20kOhm per Volt. for DC and 1k/V for AC.
This is a brochure for the latest model, the mK7. It does not have the HV range. But the text is a nice explanation of this series.
