Electronics > Repair
Keithley 2002 repair help
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nikonoid:
Thank you, Steve.

I will give it a try. I have plenty of boards to practice on. What tip temperature would you suggest?


--- Quote from: TheSteve on July 30, 2017, 05:08:32 am ---I much prefer to put a bunch of solder down the pins on one side, then lift it a little with a sharp knife. Then add some solder to the other side, grab the part with some tweezers and touch both sides back and forth and it should lift right off. With a little experience it is very quick. You can use the soldering iron to wick away most of the left over solder and then finish the cleaning with some wick, then alcohol.

--- End quote ---
nikonoid:
TheSteve,

I got a chance to try a method you recommended. It is a bit nerve racking to have a bunch of molten solder on the board. I had to get my tip temperature to 550F - this was the lowest temperature that would keep the solder molten when you go back and forth with iron. Hopefully the board is ok.

In the end I modified your process a bit, I would lift one side a little bit, then use desoldering iron with suction to remove solder still connecting lifted left to PCB and only then I would use extra solder on another half with tweeters to remove the chip.

This also gave me another proof that replacing components compromised with electrolyte is a must. Some microchips I was desoldering were corroded to the point that solder would not want to stick to them even with a good amount of flux.

Thanks again, 7 ICs are off the board now. Inspection under microscope showed no lifted of damaged pads.

I have another round of cleaning, then fixing broken lines and replacing parts. Unfortunately some of the parts are not arriving until the next week.

Meanwhile I called Keithley where I learned that top shield for 2002 is a non-orderable part - only internal technicians can order it. I can order top shield for Keithley 2001 and it is $55. Would someone know if top shields for 2001 and 2002 are somewhat compatible? Can I modify one into another?

TiN:
Okay, you hit two no-no's in my book there.

If you have to increase tip temperature over 240-255C, that is a sign that tip and/or iron you using are not fit for the job. Meaning that PCBA is dissipating more heat than you providing. That means two things : you need larger surface area (bigger solder ball blob or wider more massive tip) or heatflow is not enough (need higher power soldering iron). Raising temperature might look like it's working ok, but you just delaminating PCB. Keithley analog PCB not good to survive high temperature, and those thin pads are easy to peel off. So work on your thermals ;)

Second - pulling SOIC by one side is just making pads even more easy to damage. Keithley PCB have nSMD pads, usually connected just by thin trace without teardrops. I had number of times when pad and trace looked fine even under microscope, but actually were broken apart right at the point where pad connected to the trace. Searching for such faults wasted lot of hours.
After I started using only dual side SOIC heating, never have this issue again. Wide 4mm+ chisel tip with large solderblob flowing back and forth on both sides of IC works great. I'm using 120W handpiece to ensure good heatflow.

Top shield is same on 2001 and 2002, but there are two versions if them. One with cutout and duct for fan, and older one without cutouts, sealed type. If I remember correctly, they even have same partnumber. So I'd just order 2001 shields and be done with it :). Make sure you order both top and bottom parts, and don't forget the mounting screw! It's not included with the cover.  :scared:
TheSteve:
A different iron is needed if you need to turn the temp up like TiN posted. With the right tools and some experience it is a very quick process and will never cause any PCB damage.

And Keithley PCB's are pretty crap quality...
nikonoid:

--- Quote from: TiN on August 02, 2017, 11:07:35 pm ---If you have to increase tip temperature over 240-255C, that is a sign that tip and/or iron you using are not fit for the job. Meaning that PCBA is dissipating more heat than you providing. That means two things : you need larger surface area (bigger solder ball blob or wider more massive tip) or heatflow is not enough (need higher power soldering iron). Raising temperature might look like it's working ok, but you just delaminating PCB. Keithley analog PCB not good to survive high temperature, and those thin pads are easy to peel off. So work on your thermals ;)

--- End quote ---
TiN, I think I just got lucky on thermals. Seeing your email I went to measure the tip with thermocouple. I loaded the tip with lots of solder for better contact. Two different thermocouples I have gave me 241C and 256C, when iron was showing 550F (288C). I am guessing my iron needs to be calibrated.

I use Hakko 888D with 2mm chisel tip and I like it. Should I consider Hakko 951 or something else?


--- Quote from: TiN on August 02, 2017, 11:07:35 pm ---Second - pulling SOIC by one side is just making pads even more easy to damage. Keithley PCB have nSMD pads, usually connected just by thin trace without teardrops. I had number of times when pad and trace looked fine even under microscope, but actually were broken apart right at the point where pad connected to the trace. Searching for such faults wasted lot of hours.

--- End quote ---

Just in case I will do a very careful inspection of pads after cleaning and recheck vias in the area.


--- Quote from: TiN on August 02, 2017, 11:07:35 pm ---Top shield is same on 2001 and 2002, but there are two versions if them. One with cutout and duct for fan, and older one without cutouts, sealed type. If I remember correctly, they even have same partnumber. So I'd just order 2001 shields and be done with it :). Make sure you order both top and bottom parts, and don't forget the mounting screw! It's not included with the cover.  :scared:

--- End quote ---
Part numbers seems same for the bottom shield but different for top shield. Do I still need to buy shields as a pair, if I already have a bottom shield? Also I do not see the screw on their part list and also suspect I may need the LEXAN SHIELD, CHASSIS LEFT and LEXAN SHIELD, CHASSIS-RIGHT.

Thanks.
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