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OK the suspense is over... the next piece of TE on the bench is not the Philips VTVM but... the Rochar DMM I bought the other day.
Best 10 Euros I spent in a long time, talk about a bargain. The two ones on Ebay went for like 150 Euros !
CONDITIONMine looked rough for sure, but turns out it was just dust, saw dust I would even venture to say. It cleaned up very well and very easily.
The front of Rochar instruments is a delight to clean : the face plate comes off iun seconds : just 43 screws in the corners, and it comes off ! All the controls, switch gear, fuse holders.... nothing needs to be taken, off. The bezel also comes off easily. So it's quite easy to clean thoroughly.
3 white round stickers on the face plate also came off easily.
The design of the enclosure is everything but air tight at the rear, so lots of small debris entered the instrument. Had to remove the top and bottom cover and shake the thing at length to get the crap out of it.
But, other than this, the inside is spotless. Hardly a spec of dust, zero corrosion, it looks nearly new. An excellent surprise !
Looks really nice inside out now
Mechanical-wise, there are a few dings at the back, which you can't even really see on pictures, don't even feel the need to do anything about it, it's minor.
The most visible is the one I have already shown in a previous message : front right corner of the top cover is a bit out of shape. Not enough to spoil the fun, and is probably fixable.
CONSTRUCTIONThe unit belonged to Aerospatiale according got stickers, and was fitted with an hour counter. My unit looks like it ran for only 5,021 hours which is not much eh ?
Back plane has fat gold plated traces like the HP stuff of that era.
The boards are held by two brackets front and back. Removed them so I could take pics of the back plane and board for you. Big mistake.
One of the screws holding the brackets fell under the bench... I managed to recover it but the star washer that was with it
Then when you lift the brackets.... bit fall inside the instrument, need to dive to recover them... looking closer... these bits are small slotted plastic guides that hold the boards, grabbing them from the edge. All these guides are glued onto the metal brackets, but the glue has dried and many of these guides are now free electrons, and putting everything back together is a chore, one can easily lose his sanity of this.
So I really need to re-glue these guides... super glue I guess might be all that's needed.
Display boards : their construction is interesting... I mean the tube part in particular. The tubes are no socketed. They don't even have a plastic base with round pins to begin with. No, all you have are the barre thin wires that come out of the glass envelope of the tube, and these wires are soldered onto a tiny PCB, which is then mounted onto the display board, into a slot, at a right angle. So, very customs.
This means that the tubes are just "floating" onto their wires, hence it's impossible to get them to sit straight and all aligned. They are all crooked... so it's gonna stay like that. I will just declare it's part of the charm f this meter.... when you can't change something, instead just change the way you look at it...
ELECTRICAL TESTINGOut of the box, it appears to work quite well !
The main frame is alive, and when I use the Voltmeter part of the plug-in, it works out of the box and reads surprisingly accurately when I feed it with my cheap chinese Vref that outputs 2.5 / 5 / 7.5 /10 volts. It reads just 2 or 3 counts above perfection. Like, 2.503V or 10.002V, something like that. More than happy with that.
BTW, that range switch suggests it's a 20,000 count meter, but the mainframe actually can counts up to 25,000 and will only light up the "overload" light when going past 25,000 not 20,000.
Measurements made between 20,000 and 25,000 look just as accurate to me as those below 20,000... so I will declare this a 25,000 meter if you don't mind !
There is a " Check 20,000 " calibration position on the plug-in switch. I adjusted it spot on but it makes the meter read a tad low now, like 2,495V instead of 2.5. So I guess that means the internal Vref in the plug-in is not as accurate as my chinese Vref, so I decided to use the Chinese Vref instead, to calibrate the full scale. Sue me.
ISSUES So overall it's a one hell of a buy for the money, I am extremely happy with purchase. But of course it's not perfect, so here is what I found that needs fixing...
1) Like any Rochar TE, the orange colour filter in front of the display tubes, is dropping, doesn't stay in place. That's because it's held in place by strips of foam glued onto the chassis, that push the filter against the back of the face plate. Foam deteriorates of course and just can't hold the filter any longer.
I have already fixed that in another piece of Rochar TE of mine (my universal counter) : pull the remains of the old strips, clean the glue residue, and apply some new strips of foam... so I did that, except I could not find my roll of foam... the "garage" part of my living room is too much of a cluster fuck, not much is accessible.... I quickly gave up. I will stumble upon it one day, but in the meantime I just used masking tape ti hold the filter onto the chassis.... does the job for now....
2) The 4 little neon bulbs used for the decimal points on the display, look pretty dim and tired. One in particular : number 2 from the left. It looks even dimmer than the other 3, and sometimes doesn't even come on at all. sometime it does, but very dim and in the course of a few seconds it becomes dimmer and dimmer and dimmer and... eventually turns off altogether. Now whether the bulbs themselves are tired, or the electronics driving them is faulty... I don't know just yet, need to investigate !
3) The most problematic issue now : the ammeter part of the plug-in is very sick. As much as the voltmeter pat is excellent... the ammeter part is sick.
With no current supplied to its inputs, on all ranges it reads something ! From cold it's a relatively small but not insignificant value. I decided to test the plugins anyway and fed some current using my current limited lab power supply. This allowed me to test the two highest ranges : 2A and 200mA. They appear to work just fine and accurate, I was pleased. Disconnected inputs. Then after a few minutes the "no input" value displayed on the main frame would got up and up and up and up ! For example the 2A range would happily display 1.2A ... no kidding. After a few minutes it went over the top and most if not all ranges simply overloaded the display : " 25,000 overload " is what I would get.
I noticed that the input fuse and its socket were bad lt corroded, lot of green stuff. I fixed that. No joy.
So basically this ammeter is haunted.
So it's unusable as is. Need to fix it.... but I don't have a manual for it. Electropuce has the manual for the mainframe, but the mainframe appears to work just fine. It's a manual fo the plugin that I need, and Electropuce I think doesn't have one
I will google a bit see what I can find.
Maybe I stand a chance of fixing it without a manual ? I mean the ammeter is obviously just shunts that then feed the voltmeter part... and we know that the voltmeter works just fine. So there is not a whole bunch of circuitry that could potentially cause our problem here, I guess.
From cold it measures OK, so the basic functionality and current shunts are most likely OK.
So the problem must lie in the small piece of circuitry that's at the interface between the Voltmeter part and the current shunts of the ammeter.
The "ghost" measurements appear only after a few minutes and get worse and worse... so maybe there is a capacitive effect here, some old cap that leaks, and that leak causes trouble in the circuitry, in some way as to create a false reading, that gets higher and higher as time passes.
I don't know....
Anyway, something to investigate/ troubleshoot, that's cool.
Overall extremely happy with my 10 Euro purchase !!!
Now some pics...
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Topic: Test Equipment Anonymous (TEA) group therapy thread (Read 23607930 times)