Hello everybody.
This is my first post but I have been a reader of this forum for a quite a while.
What a fantastic resource and such a knowledgeable and helpful community!
But back to the subject.
The patient - one of AVO`s very early digital multimeters - DA 112
Health status of the patient - well... more dead than alive as it stands now.
It has been acquired from a well-known auction site. was quite visible form the photos that its condition was quite bad, apparently not working but nevertheless, as such an item is quite rare, I decided to take a plunge.
Upon arrival... here I must express my very special "gratitude" to the carrier - the only smashed parcels that I ever had all were handled by them.
And so it was this time
to add insult to injury so to speak, in addition to quite poor original condition, now I got its case and internal fixings - all broken into pieces.
although it all was quite disappointing, it got me even more encouraged to restore this grandpa.
so leaving the smashed casing issues aside, further internal inspection revealed:
1. the rechargeable battery heavily leaked
2. the meter must have been kept in quite a dumped atmosphere (if not partly submerged in water at some point) - hence the general rust patches everywhere
3. seems that moisturized air and leaking acid from the battery - created some mist that got onto the majority of the elements, resulting in:
- corroded contacts
- corroded elements. particularly electrolytic` aluminum cans (and check out that coil`s shield on one of the photos below!)
- the solder - the chemical reaction with the mist created a thick layer of, dunno how to call it properly but for simplicity let`s call it "oxidation", that you can`t even desolder components as the heat from soldering iron (40W!) doesn`t penetrate thru it at all.
house of horrors...
what has been done so far:
1. smashed case - put together to the best possible condition (there were tons of very tiny bits that was virtually impossible to put properly together and some of them were even lost), epoxy does a great job.
2. general rust form the fascia and internally - scrubbed, treated with phosphoric acid, and lacquered where required
3. Electrolytics - although some checked OK, all have been replaced (as their cans have started corroding away anyway)
4. PCB examined for dry joints (remember the huge oxidation on the solder) - fixed a few. here I must say that back then they did not try to save on solder so all joints have quite a generous amount of it and although the oxidation level is thick, underneath the contacts usually look very well soldered on.
5. Some paper in foil caps will be replaces - got them on order.
NO attempts to switch it on have been made. A bit too afraid to be frank.
Not afraid as in "scared" but afraid like in "disappointed" as by the look of it the chances are it will blow up...
Due to the corrosive atmosphere it was kept in, literally all the components need checking out and the oxidation layer on the solder doesn`t make the job of unsoldering (e.g. to lift op one leg to take proper measurements) easier.
but again, i am not giving up, just yet. It is a piece of metrology history worth trying to save, there are not many of them left out there.
Hence, guys, need your help if anyone happens to have schematics and manual for this rare gem? Looking up on the Internet did not yield anything
...
I will keep updated on progress, it is bit slow, only get time to work on it on weekends, and probably will need to ask for some help along the way.
thx
Vince
PS and of course the photos, we all love them: