| Products > Test Equipment |
| HP 3465A DMM repair |
| << < (3/9) > >> |
| Vince:
BD, this thread is lacking in the annotated schematic department... this thread needs more illustration please ! >:D |
| MrYakimovYA:
--- Quote from: Vince on May 25, 2022, 12:28:41 pm ---BD, this thread is lacking in the annotated schematic department... this thread needs more illustration please ! >:D --- End quote --- There are plenty of circuits diagrams, theory, figures, descriptions ( :P): http://hparchive.com/Manuals/HP-3465A-Manual-SNprefix-1546.pdf |
| bd139:
If only it was that easy. The revision of the DMM I have is not covered by that manual and the component placement and front end are slightly different. The only copy is the Keysight one and that's awful quality scan: |
| mawyatt:
--- Quote from: Caliaxy on May 25, 2022, 02:28:33 am --- --- Quote from: mawyatt on May 25, 2022, 01:07:17 am ---Would think you should get lower leakage and higher breakdown from the B-C junction rather than the B-E junction of the 2N3904. --- End quote --- According to this plot in the Art of Electronics, the leakage current of the B-E junction of 2N3904 is <100fA (up to ~80mV). Not bad at all... It's also smaller than the leakage current of the B-C junction at the same forward voltage. The breakdown voltage is indeed 10x higher for B-C, per the data sheet (60V vs. 6V). (leakage forward current vs. applied voltage) --- End quote --- Interesting, would not expect the B-E junction to be lower, even in forward direction!! However, suspect the protection diode in the meter is used in reverse direction and the B-C junction should have lower leakage in reverse as well as higher breakdown. How is the protection diode used in the meter? This will determine which PN junctions in the 2N3904 are best for the intended meter use. Best, |
| bd139:
Purely coincidence but I just posted the front end and clamp in my previous post :) CR9 is the faulty diode. |
| Navigation |
| Message Index |
| Next page |
| Previous page |