| Electronics > Repair |
| Agilent 34401A Bubble on PCB ... can it be saved ? (SOLVED) |
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| The_Spectrum.A_idiot:
--- Quote from: Dr. Frank on September 13, 2024, 09:32:48 am ---Hello Unknown, it's a pity that some people don't even reveal their first name. I don't like to cite SUCH alias names, in first place :palm: From a closeup of the damaged PCB, I strongly assume, that somebody tried to repair the instrument, using a hot air gun around U110, or the Ohm protection transistors Q203 - Q210, either to replace or re-insert them. That guy used too much heat, also too long, and did not cover the other components, so creating this PCB delamination. It's not clearly visible, but all components inside the area of delamination might have been damaged by the heat, at least all the solder joints are under suspect. Please make a macro photo exactly vertical above this area, so that every component and solder joint is sharp, and better illuminated, maybe from different sides. The transistors have been soldered very badly, and I see solder balls. The transistors might be defective, or there might be a short to GND as well , via Q211 which should be tested in situ. If you select 4W Ohm, do you measure the appropriate test currents out of + Input and - Input for the different (manually selected) ranges? You have to de-solder these transistors anyhow, so you can test them individually, later on. W/o the transistors back in place, you might then solder a short from Q202 to CR202 temporarily, to make further tests on the Ohm mode. Descriptions how to do that, has been written down elsewhere .. I guess you found that thread already, as you copied the OHM schematic here. I guess, that U110, that is used for current mode protection, has been replaced, but that mode should work properly, and has nothing to do with your OHM problem. Anyhow, many of the solder joints look very bad. U304 also looks bad. We will definitely continue analysis, when you have presented further results. Frank --- End quote --- If you select 4W Ohm, do you measure the appropriate test currents out of + Input and - Input for the different (manually selected) ranges? -- What do you mean exactly ? IF the instrument measures the proper value of a plugged in resistor ? no. not at all. you want me to plug a multimeter in mA mode and measure the output current between the LOW + and - ? W/o the transistors back in place, you might then solder a short from Q202 to CR202 temporarily, to make further tests on the Ohm mode. Descriptions how to do that, has been written down elsewhere .. I guess you found that thread already, as you copied the OHM schematic here. I was also a bit in the dark as I didn't really grasp what that schematic meant , and under what conditions the instrument was under .. so I would like some further insights from you if you have the chance. Thanks |
| inse:
That is a somewhat botched repair (attempt). Someone with too much hot air and little intuition had been at work. But don’t worry, with love, patience and enamel wire it can all be fixed. First I would remove the SO8 chip to check where the traces went, then restore missing ones with enamel wire. Use flux to reflow the other components. |
| Sorama:
Why not replace all those visibly “impacted” devices by default ? Takes 10’ of soldering. That would also allow one to clean and inspect the pcb. |
| The_Spectrum.A_idiot:
--- Quote from: Sorama on September 13, 2024, 05:55:20 pm ---Why not replace all those visibly “impacted” devices by default ? Takes 10’ of soldering. That would also allow one to clean and inspect the pcb. --- End quote --- Due to the fact the PCB is so badly delaminated , I want to do the bare minimum to reincarnate the device. as far as I know if I whisper a bit louder it would break everything else that might be kind of working. So I am trying to do as much testing and diag BEFORE loading the parts canon. Thanks |
| wraper:
I'm 99.9% sure someone fried it with hot air so much that melted front/rear switch and water vapor popped the bubble in PCB. As already mentioned the main concern is vias. As there does not seem to be any traces on internal layers, worst case broken vias can be fixed by running thin wires through them and soldering on both sides. |
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