In Other News...
Looking like the resistance measurement issues with my 3478A are in fact F/R jack switch-related. Cleaning seemed to help; went from fluctuating between .6 ohms and .3 ohms shorted (using banana patch cords, not clips; these measure 0.9 ohm and 0.045 ohm on my Fluke 189 and DE-5000 respectively) down to fluctuating 0.22xx - 0.19xx ohms. After reviewing the schizzmatics, I discovered I could bypass 1/2 of the switch by swapping a couple leads at J107; that dropped shorted resistance to 0.116x - 0.1170 ohms.
Part of me is saying, as I know I'm likely going to really want the rear jacks about twice in my lifetime, that I should just bypass the switch completely and solder the front ports into service; it'll be more accurate and reliable anyways... meanwhile, the purist in me keeps trying to strangle that part. We'll see who wins after dinner.
mnem
"There's no rest for the wicked, but the virtuous have no pillows."
That switch was my first and only suspect for the cause and also the only part of the meter that is likely to be dormant for long periods. As such it would allow crud to be building up undected until someone activated the switch and allowed crud to migrate courtesy of the contact wiper which has some under its wiper. I'd give it another of contact cleaner and give it some beans while operating the switch remove that crud, also I'd try some pure alcohol on it, nothing to lose. [emoji38]
I've tried spraying contact cleaner in it three times; gently lifting up the top cover so I can spray inside. Last time I undid the metal stakes and removed the spring & ratchet so I could lift that end to spray inside. I'm considering to remove and immerse in alcohol while working back/forth as a last ditch effort before attempting to disassemble; it's almost as much work as disassembling though.
mnem
I'm eagerly awaiting the arrival of my latest acquisition, another Tek TDS210, not that I need another but it comes with a differential probe, something I have been looking for at a sensible price.
Wow, isn't that probe worth more than the scope? Nice score.
Well ordinarily yes but this one was incomplete, but I sorted that and it only has a bandwidth of 25MHz. Apart from that it is almost brand new and comes with its own pouch and manual.
Fine then... you're only half a Jammy Git today... a Jammy Gih...?
Tant-Slayer? Without a doubt. I hate the little bastards.
"Necromancer of Test Equipment"? There you go with them big words again. I had to look that up. Wizard or Warlock practicing the occult such as raising the dead. OK, I'll buy that. I've brought numerous pieces of test equipment back from the gates of hell and made them useful again. I've also killed my share. Just yesterday through my own carelessness and stupidity I had a fatality. And I'm not gonna say right now what it was and don't ask because I am super pissed at myself. It's gonna go in the DOA (Dead On Arrival) closet to perhaps work on and possibly revive at a later day. But I don't hold out much hope that my future necromancy will work. We'll see.
Agitator-at-large? Absolutely. Never pass up the opportunity to create chaos and watch the hilarity that results.
You see, that's where the Necromancy part comes in... as with Alchemy; for everything you gain, something must be sacrificed...
The transistor testers seem to misbehave on RF transistors. I’ve got one that won’t read an MPSH10 and that’s not that fast. Was oscillating in the fixture.
Current is about right for that circuit. Might be weak transistor. Only way to really find out is replace it. This is quite common in high Ic circuits I’ve seen.
Mmokay... So I guess my question is... did I remember this right from back in the radio cave with grand-dad, or am I completely blowing smoke out my arse? Either is quite possible today...
I'm not the greatest with RF, but with active notch filters like this one, it's my understanding that overall gain is supposed to be relatively small, somewhere between unity and a few dB. But what's important is how much the device lowers the noise floor so that you can receive weak signals being sent at the correct frequency (and only at the correct frequency) with clarity. The lower the noise floor, the less noise gets amplified in the next stage.
I'm sure bd or med can explain it better than I; I'm a bit of a hack as far as RF goes.
mnem
*Kindof buzzing on 4 hours sleep and 3 cups of coffee*