Electronics > Repair
[SOLVED] HP 34401a - Error 612, 613, 615, 617, 618, 619, 621
Resonant:
Well its all fixed a replacement input cap from CPC (CA0708) and some Panasonic FR series 105C Caps for the PSU and all working properly again. I checked all the 13k input resistors to make sure they had not been stressed and they were all in spec. So after a calibration all working well and stable so I'm very happy.
HighVoltage thanks for the tip on moving through the calibration sequence :-+
free_electron:
Yup. those blue stinkers short out sometimes.
same for the craptalium capacitors. i knock those out by default.
abnormalalien:
Hi all,
I'm also working on a faulty 34401a and was wondering if you could explain some of the stuff you've mentioned earlier in this post?
I (guess incorrectly) posted my own thread explaining the particulars of my machine's situation (https://www.eevblog.com/forum/repair/hp-34401a-repair-fails-st-606-609-610-612-613-615-617-618-help/) but long story short, there's something wrong in the Ohm's Current Source part and prob elsewhere too. On here, I've seen several people print out Dr. Frank's schematic and write in their own measurements but I'm a bit confused. I've been assuming the boxed values are what we want; was this run through a circuit analysis software or did you all figure that out by hand (shudders)? Mild curiosity aside...I'm quite unfamiliar with electronics, especially at this level. Can someone let me know exactly what voltage drop I'm supposed to be measuring?
For example, on the far left of the diagram, there's a +7REF line, which you have measured to be 7.012 or 6.994V. You plugged high on a working meter into pin 3 of U201-A? Or somewhere else? Lo is then ground via pin 4 on U201-A? Or lo is the white power line ground from the power schematic? (Does it matter?) What about for the boxed value 12.750: how is that done?
Any advice is much appreciated! Thanks.
Zucca:
--- Quote from: abnormalalien on May 24, 2018, 05:33:24 pm --- I've been assuming the boxed values are what we want; was this run through a circuit analysis software or did you all figure that out by hand (shudders)?
--- End quote ---
The boxed values were from my bad unrepaired unit, the one written by hands were from the good Dr. Frank's unit. All of them were measured values from real life.
Beside that, it looks like you have problems to understand a schematics, where the pins are and where to put your DMM probes. I could give you more advises but I am worried you will understad them in a wrong way so please post pictures of what you are measuring, how you do it and where you put the DMM probes.
Worst case we will tell you: You are wrong.
As long you keep your DMM in V reading mode you and the circuits are safe. So you could even do some tests by yourself and with your active brain you will be surely understand some electronics black magic secrects.
There is main voltage in the 34401a, please be very very careful to stay away from that corner.
PS: Do you have hot air (de)soldering equipment? Probably you need to replace some SMD components and without it you will be stuck.
abnormalalien:
Ah ok that makes sense, I apparently missed that. Written values = functional, got it.
I appreciate the concern; while I'm a bit :-// on the electronics background, I have no intention of dying for my thesis! I once tried to design/implement an electron beam evaporator which involves a high voltage (1500-3000V) but low current circuit using thoriated tungsten wire. This combined two of my biggest discomforts in the field: electronics and radiation...I wound up burning some hair off my arm at 3000V. Yea, that's when that project stopped being a priority.
I understand some basics; I can identify most of the circuit symbols including ground. I think ground is just something that's never really clicked in my brain. Talked to the advisor about it last night; I've been informed there's two, analog and digital, but that in general when I'm troubleshooting, I can probably just use the green line directly connected to the case. Somewhere that ground is connected to power ground (white line in power).
I've attached a couple pictures. In the first you can see I've got a (working) Keysight and a Fluke meter. I'm mostly using the Fluke but occasionally checking results with Keysight. In this one you can also see my lo on the fluke connected via an alligator clip to case ground. I've got a red probe for the positive terminal and have been using that to check voltages. In the other picture, I've circled the U201. As I've understood from this and other sources, that's a common failure. To measure the U201, I would just use my positive probe to check each pin directly?
Ah I'm not sure about the hot air soldering gun. I've got both large and micro soldering stations and I can probably borrow one from another lab in the department. (Most everyone is DIY here, someone's got to have one.) Or I might have one stored in my Dad's old tools. Can check this weekend.
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