IET VI-700 Precision Voltage & Current Source full manual sought. - Page 1
Forum section: electronics / general

author: AB9GO
author_rank: Contributor
timestamp: May 01, 2020, 09:41:47 pm
content: Hello all,I have a IET VI-700 Precision Voltage & Current Source (base model, no options) that has not been calibrated since it was manufactured in '95. IET's website has a manual download but it has been castrated (calibration procedure and schematic removed). Is there a .PDF on the web for the cal and schematic? I have looked to no avail. Even a smart phone snapshot of the info will work. I'm not that particular as long as it is readable.Thanks,Randy AB9GO

author: alm
author_rank: Super Contributor
timestamp: May 01, 2020, 11:18:09 pm
content: I have one of these in parts waiting repair. I think mine had a broken transformer that I had to replace, and a charred output resistor that also charred the PCB. Possibly a dead op-amp. Back when I got it, I was able to get some information. No complete schematics, but I got the manual with calibration information. I inquired about how to convert it from 110V to 220V, and I received some documentation that showed PCB diagrams. Despite these appearing to come from assembly documentation, I was not able to get more complete assembly documentation, never mind schematics. I hope this helps!

author: AB9GO
author_rank: Contributor
timestamp: May 02, 2020, 11:35:31 pm
content: . Thank you for the upload. It is the manual I was seeking. Looks like 14 others were looking for it too!My unit is in working condition. If you need any measurements or part IDs let me know. I'll be glad to pop the top off.Randy. AB9GO.

author: alm
author_rank: Super Contributor
timestamp: May 03, 2020, 12:17:53 pm
content: You're welcome!Actually, yes. The reason why I haven't put it back together yet, apart from having a backlog of other repair projects, is that I was not entirely sure of the value of R48 (when looking from the front, near the left edge of the board behind the two pin headers). The PCB was charred around R48, and the bands on the resistor were very faded. I measured it as 40 Ohm, but my best guess from the bands is yellow white (4.9 Ohm or 49 Ohm). Could you check the markings, and measure it? Measuring in circuit should be fine, the circuit measures > 1 MOhm with the resistor removed in my unit.If you want to test it, if you could set it to e.g. 1.9V and briefly short the voltage output, what is the voltage over R48 (I measured 12.9V), and does it get awfully hot?In my tests the poor resistor was dissipating over 4W while delivering almost 400 mA into short-circuited, which seemed like a lot for such a small (2-3W?) resistor. My unit does not have the HP (high power) option for increased output current. From my limited reverse-engineering of the circuit, there did not seem to be any active current limiting beyond the resistor. Just the overload LED coming on. So I figured maybe the value of R48 should be much higher? I would expect a unit like this to survive being short-circuit indefinitely without charring the PCB.On a side note, I briefly investigated if upgrading the reference, from LM369 to e.g. LM399 or AD587, would improve stability. But I measured both the LM369 output and 10V output from the terminals for 5.5 days, and over that period the LM369 changed by 4 ppm, while the 10V output changed by 17ppm. So it seemed to me that the stability is mostly limited by the regulation / output stage, and not by the reference.

author: AB9GO
author_rank: Contributor
timestamp: May 07, 2020, 12:20:58 am
content: Hello. I took a look today and the resistor is marked 39and .01%. There was no overheating on my pcb or resistor.I hope this helps!Randy AB9GO.p.s. The max supply ma. for the standard reference is only 70 ma so 400 ma is way to much.The standard model may still beused within the overload condition and will functionfor approximately 50-100% overload with only a slightdegradation of specifications.So the max I'd use is 100 ma.

author: alm
author_rank: Super Contributor
timestamp: May 07, 2020, 07:38:38 pm
content: Thank you for opening the covers and taking the picture! That confirms that my resistor was okay, although I will still see about replacing it with one with a higher power rating. I agree that 400 mA short circuit for a supply rated for 70 mA (with up to 140 mA overrange) seems way to high. But looking at the circuit, I did not see any indication of any attempt to limit the current. So my guess was that my unit in its previous life spent many hours with shorted outputs, and that with more normal usage, the overheating would not have happened. Do you know the short-circuit current of your unit?

author: AB9GO
author_rank: Contributor
timestamp: May 08, 2020, 07:03:22 pm
content: Set for 19.99 VoltsI have a short circuit current of .39 Amps. I believe yours is working okay it's just somebody abused it in the past. 😡 Replace the caps and the burned resistor and I bet you will be good to go. Interestingly the last selling price of the unit was around $1,400!!Randy AB9GO.P.S. my unit has the original caps and they are a hodgepodge of name-brand and no name brand capacitors. mostly brands I never heard him before out of Korea. I'd suggest replacing them all I'm going to. also my unit was supplied with a rubber coated power cord that is starting to fall apart it's getting replaced to but otherwise the units in really good shape.

author: alm
author_rank: Super Contributor
timestamp: May 09, 2020, 10:42:00 am
content: Thanks a lot for checking that! That means I don't have to go on a wild-goose chase trying to find a current-limit circuit. Mine indeed also has a mix of Nippon Chemicon branded-caps, and brands I've never heard of. It has a standard IEC mains socket, so no problem with the power cord.

author: AB9GO
author_rank: Contributor
timestamp: May 10, 2020, 12:56:39 am
content: You are lucky that yours has the IEC connector. Sure would make it easier to change the power cord if I had one!.Quote from: alm on May 09, 2020, 10:42:00 am