ebay Keithley 2000

[grumpydoc]

Spotted this K2000 for sale on ebay.

http://www.ebay.co.uk/itm/Keithley-2000-Digital-Multimeter-/182495577197?hash=item2a7d95846d

Nothing especially strange there.

Except take a look at the PCB





According to the schematic U131 used to be an LM339 quad comparator but I am puzzled as to how the PCB got into that state. It looks like it vaporised, or caught fire.

Either that or a very ham-fisted desoldering attempt.

Suggestions, anyone?

[alm]

I find it hard to believe that even ham-fisted soldering would damage the PCB so locally, so my guess is a severe overload. I can not immediately see from the schematic where the OHMA node is connected to, but looks like it senses the high voltage and adjusts the current source if that is out of range. So maybe a severe overload on the sense connections could do this? I know there are a bunch of series resistors, but the sense terminals are only rated up to 350 V and I do not think they are protected by spark gaps of MOVs, so maybe feeding them 1000 VDC could do this?

After that somebody tried to desolder the part and ripped off all those pads.

Looks like a nice project for TiN if he is bored .

It is funny that all self tests pass. Guess they do not test that part of the current source, and means that repair might be feasible assuming you are skilled at repairing pads. But obviously in a severe overload a bunch of other components could be damaged. Though nothing else in the picture is obviously damaged.

[MadTux]

K2000 board is most certainly 2 layer only. So you can always mill/dremel out bad spots on PCB and epoxy in some new dual layer PCB blanks and recreate the old traces with a fine dremel grinding bit. Did that a few times sucessfully on various THT boards. K2000 board is more delicate, so using a CNC engraver to route the traces might be a better option.

[grumpydoc]

I see someone else spotted it https://www.eevblog.com/forum/chat/looks-like-interesting-repair-challenge/?topicseen

It is getting strangely tempting to have a go, after all attempts have been made at repairing K2000's which are in much worse state.

However, the current bid is very close to the maximum I'd be prepared to pay once postage is added.

[Yansi]

This might be a third thread here regarding this Keithley.

[grumpydoc]

Well, that went for about twice what it was worth. £150 plus £15 postage

Is it just me or is that too much?

[alm]

Agreed. (Mostly) working models go for only slightly more than that, and this one requires a major repair and may well have other damaged components beyond the comparator.

[razberik]

Prices inflated by eevblog.