Products > Test Equipment
Keysight 34465A reliability
Smith:
--- Quote from: alm on April 22, 2022, 06:41:11 pm ---Glad you caught it before another transformer died!
I'd expect a primary side fuse that blows if the instrument is using 10x more current than expected. Is there none, or is it slower than the thermal fuse at this current level?
--- End quote ---
There is a primary fuse, not exactly sure what is is rated at. I guess it just overheated until the thermal fuse went out. Probably for multiple months, until it died entirely.
About the solder flux residue. I don't have a big problem with it unless it is at a high speed path, of a low level measurement path. This tends to give problems in the long run, particularly with higher levels of moisture in the air.
I see lots of flux residues in higher end measurement devices, especially with user selected options from the factory, big input/output connectors, and bodges. Actually, it f you cant see it, its not potentially dangerous for you or the device, is it really a problem?
Kleinstein:
For the flux residue it depends on the type of flux. Some flux is corrosive and must be removed. Other flux is OK even in higher humidity conditions and works as a reasonable protection and may be preferred over a "clean" surface. With some parts fited (e.g. switches, cables, relays) is may be very hard to get a good clean. A poor attempt on cleaning, so that the flux is no longer visible can do more harm than good.
The main reason for the primary fuse is to prevent a fire in case the transformer fails, not to protect the transformer from overload. It would be nice to have also some protection for the transformer, but this is tricky with quite some tolerances in the fuse tripping points and possible inrush current spikes.
tooki:
--- Quote from: AVGresponding on April 23, 2022, 04:12:57 pm ---Yes, I understand; it's more practical to create a mod-board than to re-spin the main one, usually.
--- End quote ---
Do you understand, though?? This isn't a mod board as such. A mod board is commonly understood to mean a daughtercard made to implement a bodge to correct an error on the main PCB, rather than making a new main PCB.
As I explained above, early versions of the board had this part of the circuit on the main PCB. Then on this later version, the main board was respun to move that part of the circuit onto a daughtercard.
This isn't a cost-saving measure, as it's more expensive in every way: the added engineering cost, a respun main PCB, a new daughtercard, and the extra labor to solder the daughtercard onto the main PCB.
tooki:
--- Quote from: AVGresponding on April 23, 2022, 02:56:53 pm ---I know, but that still doesn't make it ok
--- End quote ---
As wraper said, cleaning in situ could get flux residue into places it shouldn't be. And with the two boards soldered together, cleaning becomes much more difficult.
So you'd be adding a cleaning step with no advantage, but plenty of risk.
I guess you don't open many devices. If you did, you'd have noticed the flux residue found in all sorts of equipment, from consumer electronics to IT to test gear to appliances.
Kleinstein:
The part in the red rectangle looks a lot like part of the overvoltae protection. A good guess on the parts are 2 back to back depletion mode MOSFETs and that 2 units in series. This can be used as sereis element in the input protection, though is may fail over time from high energy ESD or similar events with very high voltage (e.g. > 2000 V). A separate board could ease repairs and maybe give the option to offer different versions with even better protection or meeting other regulatory limits (e.g. military not comftable with FETs used for protection). So having this somewhat vulnerable part on a seprate daughterboard is a very reasonable thing.
The KS meters did have some problems with the maximum votlage specs and this extra board could be reaction to this, though the rumors were more pointing to the relay voltage rating as the cause.
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