| Electronics > Repair |
| Keithley 2002 repair help |
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| nikonoid:
Guys, thank you very much for suggestions. It took me few days to find time to try them. First of all I got a cheap iron tip thermometer from ebay, calibrated my iron and used it at 250C. --- Quote from: WastelandTek on August 07, 2017, 03:14:15 am ---You might try some no-joke RA flux, I use MG chems 835, pretty aggressive stuff. --- End quote --- I had MG chemicals 835, both older bottle (stuff is more like a paste by now) and fresh bottle. It helped in few places, however did nothing for vias affected with electrolyte. Tip cleaner worked better there. Used it very sparingly with a tip of a toothpick. It looks cool under microscope. I bought the silver plated Kynar insulated 30awg wire and I am very impressed by it. I removed solder bridges and made all the trace repairs with this wire. My multiple attempts to get the wire to go through the hole did not work. Maybe a wire is too large for microvias. Nonetheless I was able so to solder it partially going in. Pictures are coming. I will have to try TiNs "going through the via" suggestion another time. In the end I had to do two trace repairs and 3 bodge wires. Luckily they all are power related, not measured signal. It took 8 hours to repair the board and solder all ICs and capacitors back. Electrolyte compromised areas are not fun to work with. After this I partially reassembled the meter for a quick power up test. It came up without a hitch. As I was shooting a thermal image of it, I noticed a diode CR119 getting really hot. It was shorted and somehow I missed it on initial check. I did not have a replacement handy for this BAV103 250V switching diode. I had a 600V zener diode in a similar package (BYD57J), so I used that for a quick test. Proper part will be in next week. With this zener unit powered up with thermals looking much more reasonable. Small U108 regulator (78L05A) was getting to 180F, but apparently it it is specked to at least 250F. This time I did the open inputs test and got errors: 306.1, 306.2 ohms current source 308.3 2M Ohms overload 400.5 +4.48V DAC output 401.1 Regulator (not sure what this is yet). My next action item is to check all voltage rails before tracking these individual errors. Thank you everybody for your your help this far. |
| TiN:
That's it, no more errors? Looks too good to be true :) |
| Kleinstein:
The DAC error and the 401.1 regulator error might be hiding more to come. AFAIK the DAC is used extensively in self-tests (that't the main purpose of it) so some self test might not really work right now. The list is rather short and the first two errors might even be related. Still I would start with the other two errors. |
| martinr33:
For corrosion repair you want this stuff: http://www.mgchemicals.com/products/prototyping-and-circuit-repair/prototyping/liquid-tin-421 I use it for battery contacts. First application dissolves off the crud, rinse, apply again for tin plating. The plating is rough ( not shiny) but it works well, and readily takes solder. Well worth having a bottle to hand. |
| nikonoid:
Shorted diode replaced. New round of testing shower problems with power rails. Repair manuals does not clearly define some testing points. They refer to some diagrams like 2002-100 but I cannot find any of these diagrams available. If someone has it, please let me know, otherwise I might have to produce my own. There are lots of unmarked test pads in the [power supply section, but no description. Attached is a very rough draft. I am not very sure about difference between COM, Isolated Common and Digital common. As per power supply testing procedure (also attached) step 3 (U108) gave me 15 volts :palm: instead of 5. I think I installed a right part (LM78L05ACZ) and in proper orientation. By the way this is also a part that is getting really hot. What could it be? Step 4: U110. I am getting 1.4V instead of +5V Then +15 and -15 are just fine and bootstrap is a bit high 38.9 and -38.8. U105 is producing something completely wacky with with 1.4V and -7V And last two steps (11&12) again completely fine. U108 was replaced by a new part, the rest of regulators are originals. What would be my next thing to check? I am especially puzzled by getting 15V instead of 5. Thanks a lot. |
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