Products > Test Equipment
My poor mans SMU - The Agilent 66311B
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ve7xen:
I gather everyone is probably tired of my blunders and repair attempts, but one final post...

tl;dr after 6 hours of work tonight, my 66311B is fully operational and now has front-panel outputs!



The longer story is that the first thing to replace was the FFC cable, since I ripped that. Parlex 100R8-305B worked, though it's slightly shorter than the stock cable and more care was needed when re-attaching the front panel. Yet another thing I don't really like about the mechanical design of this box is that the flex has to go around a fairly sharp bend as it leaves the front panel, which created a kink at the stiffener and made it easy to break.

First things first, I replaced the obviously burnt UCN5812 with a new HV5812. Having never soldered PLCC by hand before, I didn't realize that this package is the spawn of Satan. After some fiddling around I got that installed. Added two bodge wires to the VFD pins in place of the pads I had damaged while removing the dead IC with a poor technique. A lot of hassle would have been saved if I had a hot air station...

At this point I also elected to replace the MAX773 DC-DC driver (which actually creates a 40V supply, not 12V as I had originally thought), because I thought it was also dead since there was no output on the regulated output pins. In hindsight the removed part may be functional, since the DC-DC in this design uses an external drive transistor and the internal outputs are not used.

These being the parts I suspected most strongly, I decided to give the board another try at this point. With the VFD sitting free and some pressure applied, I could now get all segments to light when powered on. There didn't seem to be any indication of activity on the display, just all segments lit. An hour or two of probing later I was pretty positive that the power supplies, drivers, and microcontroller were working properly. So being stupid, I decided to try soldering the VFD back on, just in case some pins weren't making contact and causing the all-segments issue. Of course this failed, and I had to desolder the thing again.

Now we're here:



I should have just replaced the pesky LM339 to begin with, I purchased one and it was cheap and easy insurance. The one on the board seemed to be working, but I replaced it anyway. Immediately the VFD showed signs of life, though I wasn't able to get a proper display until it was soldered down. There wasn't much else left to do. During my previous probing I had already determined that I was pretty sure the transistors and other ICs on the board were working perfectly, so pretty much the last ditch was to power it up and cross my fingers. And lo and behold! It's alive!



So on to the front panel output mod. In my rummaging looking for replacement parts, I had found a pair of these Pomona 72913 jacks in red and black from a long abandoned project:



They were very close to fitting perfectly in the existing front panel cutouts. I did have to enlarge the holes by 1mm or so, but it was an easy fit. Somewhat unfortunate that they are 'safety' jacks, but I felt I would have a hard time mounting the traditional type due to the depth and size of the holes in the plastic. Plus I had them on hand. With the holes enlarged, they mounted easily. I chose to solder directly to the bottom pads of the rear output connector. My first whack at this had the wires interfering with one of the mounting standoffs, so I had to redo it to avoid that. My choice was to bring the 'remote' sense lines from the connector to the front panel and short them directly to the output there. Without adding a switch, this means I won't have remote sense capability, but that was a feature I was unlikely to ever use anyway.

With these jacks there is not much clearance between the chassis and the bottom jack, but it's enough. I would recommend filing the sharp edges off the chassis or adding some rubber or something to avoid damage to the wire.



Finally I replaced the broken switch on the rear panel for calibration inhibit. And now I think I'm done breaking things. Time for an Old Fashioned ;). Perhaps a fancy knob will be in my future.

Hope this helps or that someone has enjoyed my repair log, even if maybe I should have created my own thread ;).
stuartk:
Ve7xen That's a really impressive save :)

I'll likely organize a group buy for knobs and any other Keysight parts when I'm back to the office in a week..

Don't bother getting the feet from Keysight. I contacted them and they are 19$ Cad per FOOT..  Buy them on eBay instead..

More details to come. You can pm me if you are interested. My apologies if I don't respond for a week. Canada is a bit expensive to ship from, so probably this group buy would be best for USA and Canada
macboy:

--- Quote from: ve7xen on March 10, 2016, 09:16:34 am ---...Having never soldered PLCC by hand before, I didn't realize that this package is the spawn of Satan. After some fiddling around I got that installed. Added two bodge wires to the VFD pins in place of the pads I had damaged while removing the dead IC with a poor technique. A lot of hassle would have been saved if I had a hot air station...

--- End quote ---
Good work on the successful repair.
Next time that you need to replace a PLCC, remember that you are trying to save the board, not the dead device. Clip all the leads off close to the package, remove the legless black blob, then desolder pins one by one easy as pie. Use some braid the clean up the pads, and you are ready to solder on the replacement, which is a much easier task than removal.

stuartk: I am definitely in for one knob in a group buy.
ve7xen:

--- Quote from: macboy on March 10, 2016, 01:09:00 pm ---
--- Quote from: ve7xen on March 10, 2016, 09:16:34 am ---...Having never soldered PLCC by hand before, I didn't realize that this package is the spawn of Satan. After some fiddling around I got that installed. Added two bodge wires to the VFD pins in place of the pads I had damaged while removing the dead IC with a poor technique. A lot of hassle would have been saved if I had a hot air station...

--- End quote ---
Good work on the successful repair.
Next time that you need to replace a PLCC, remember that you are trying to save the board, not the dead device. Clip all the leads off close to the package, remove the legless black blob, then desolder pins one by one easy as pie. Use some braid the clean up the pads, and you are ready to solder on the replacement, which is a much easier task than removal.

stuartk: I am definitely in for one knob in a group buy.

--- End quote ---
Thanks for the tip. This is actually what I tried, but using a sharp x-acto knife to cut the leads, which has worked well for me before on (T)SO packages. The cutting pressure was a bit much and a couple pads tore off, so I switched to heat shielding the rest of the board and using the heat gun... I didn't think to try side cutters which there might just have been enough room for. Next time :).

I actually found soldering the new part quite challenging also. Because of the way the pins curl under the package, there's quite a large gap at the edge of the part between the pin and the pad. Guess I need more practice, so now to find some other stuff to repair.
nctnico:
I did some further testing on my 66311B regarding the temperature sensitivity. The reference is pretty much stable after a few minutes and doesn't vary much with a changing room temperature so the conclusion is that the rest of the circuitry causes most of the temperature drift and therefore it doesn't make sense to put a better reference chip in the 66311B. Mine has an MC1403 2.5V reference by the way.
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