Done. Everything agrees with your readings including the distorted sine wave at the output of U740. On to that tunnel diode.
Good.
With the 2.5 division 1kHz sinewave and trigger level roughly centered, u740.9 looks like this... Ignore the intensity variation, but note the 1 division gaps in the vertical dimension; they are due to the tunnel diode nonlinearity. If you don't see those, then the triggering won't be working correctly - could be the TD biassing (follow the manual procedure) or u780 outputs or another fault in that region.
BTW, if you do chuck it out the window please make sure it is in a box with my name on it, and there's a waiting UPS van
I'm getting a solid distorted waveform with no gaps. I did try changing the tunnel diode with one from a 465 but it's a different P/N and there was no change so for now I'm assuming CR751 is OK. (I reinstalled the original). So more troubleshooting.
I didn't have the gain turned up high enough. Here's the waveform at tunnel diode CR751. it appears to be working properly but still no trigger lock.
Now that I've determined with a certain level of confidence that the "front end" of the A Trigger circuit is OK up thru CR751 I now find myself pushing up against U780 again. I've been over that ground for the past 2 weeks and can't determine why the damn trigger light is stuck on. So before I totally lose it and do something brash and stupid I'm putting this 485 aside. I'm on vacation all next week (painting Lady Copper's deck) and when I return I'll determine what I'm going to do. Strong thought process right now is a total "cop out" and buy a 485 junker and just swap out the Trigger board and be done with it. This 485 didn't cost me a lot of cash so it may be worth in the end and I'll have a parts mule. But for now I'm just plain pissed off and want nothing else to do with it.
Wow! Now, that's a nice cover.
Looks like it belongs on med's bench. Would fit in nicely.
Now that I've determined with a certain level of confidence that the "front end" of the A Trigger circuit is OK up thru CR751 I now find myself pushing up against U780 again.
The front end
does look fine, but there are TDs and other stuff between cr751 and u780. Have you set or changed the bias trimpots for those TDs?
One problem at this stage is that there are feedback loops from u780 to the TDs, e.g. via q768 q778 and similar.
Here's a couple more images. Timebase 2ms/div, 100Hz (N.B.!) sinewave input. Note DC coupled, with 0V at the bottom of the screen. The picture at 1V/div is the "out TD" TP, the one with 2V/div is the "arm TD" TP. The amplitudes are constant, but the relative timings of the various steps depend on the input frequency, the timebase, and the holdoff (set in the normal fully ccw position).
Note that the various voltage levels are a function of whether q768 and q778 are conducting or not. I'd look closely at all the voltages around there (inc q802 etc).
Just found a strip merchant. eBay user goodmeasures is buying old HealthKit stuff up and selling the guts
Taking the HP 1740A off to its own thread here: https://www.eevblog.com/forum/testgear/hp-1740a-power-supply-burn-up/
A certain D. Jones did a video about a 1740 where the rectifier was faulty.
Nope, that was 2 videos that Dave did, I did a link to them a while ago because he also used about 5 meters with the min/max feature on them because he was power rails go down at odd times. Can never have too many meters
Anyone interested in the older brother to the K20-5280A?
There is one on the favourite wallet draining site at the moment in the US.
5280A
eBay auction: #254336971401David
What did med say? Bunch of comedians here ....
Huh...
https://hackaday.com/2019/08/22/electric-dump-truck-produces-more-energy-than-it-uses/
mnem
*back to house-packing hell*
Very interesting truck but it does operate under very limited set of circumstances, where else do you regularly come across a situation where something climbs to the top of a hill empty but always descends heavily laden where gravity alone provides more enough force to propel the vehicle all the way to its destination, so the power generated is then stored and as a result of the huge payload and the resultant recovered energy as a product of the speed and gravity effect has the unique ability to produce more energy then it uses?