开云体育

A few weeks ago, I reported a problem with my 3456A where it would fail at startup with "--------" on the readout and fail Test 3. I reseated one of the microprocessors and the problem seemed to go away. Since Service Note 3456A-13A states to discard the chip sockets for all three microprocessors and solder them to the board, I figured the problem was in those red chip sockets and decided instead to replace them with good quality machined sockets as I believe others have done as well.

Unfortunately, after replacing all three sockets, the problem persisted so I started down the troubleshooting steps in the manual and one of the very first things it says to check is +5V on U13 (one of the microprocessors). I was surprised to find that to be at 4.7V or, possibly, a few hundredths under that. Since I had replaced all the electrolytics in the power supply, an off voltage like that was something I did not expect at all. Checking that rail at the power supply board, though, showed it to be around 5.1V.

Knowing that Service Note 3456A-14A addresses an issue with faulty grounds (via some riveted ground lugs), I decided to ensure the In Guard board was properly grounded so I jumpered one of the GND test points on that board to one of the GND pins on the power supply board and the meter immediately started working. If I remove the jumper, the meter stops in its tracks and restarting it produces that same "--------" and failed Test 3.

I can detect about 0.5 ohms from the pin that connects to the power supply and the pin that connects GND to the In Guard board and apparently that's just enough resistance to drop the voltage low enough to cause the processor to stop so better grounding is in order.

While I'll probably go with the Service Note's recommendation and replace the rivets with #2-56 screws, nuts, and lock washers, I'm wondering why it might not be a better plan to simply route ground wiring from pin to pin as needed. I see where that was done from the factory from one or two other pins and it would seem that a separate, soldered wire might be better off since tiny screws might tend to need cinching up from time to time to ensure they're still tight.

Has anyone here performed the rivet replacement? I suppose I'll stick with that since it's recommended (and will include a drop of DeoxIT under each lug as well) but was just curious as to whether a separate wire would be a better plan.

Thanks,
Barry - N4BUQ