Products > Test Equipment
8116A Code 42
MarkL:
Yes, that would be the right calculation. Clearly the current through R531 dominates. The power dissipation could also be different at different DC voltages, but we're just trying to get a ballpark here. 140mW is ok.
When adding currents, yes, the sign is critical since that indicates direction. If the currents were a little closer in this case, and one was of the opposite sign, it could make a significance difference in the emitter current.
Ok, so maybe something is wrong with the trigger output driver. I don't want to get too far tangent of the initial problem with the main output, but maybe this is worth spending a little time on. You could start investigating with a terminator on the trigger out directly (with nothing else) and probe R265 with a 10x probe. Make sure you use a spring ground clip to minimize ground lead inductance effects. See if you get a similar waveform. I am not sure where ground is on your waveform captures but the signal should be (approx) 0V to 2.5V with minimal overshoot.
For Q503 current, you could calculate it via R531 and R532, and for Q504 via R530 and R532. Some of the current is being siphoned off by the bases on Q505 and Q506, but it is probably not significant compared to the total current.
Mick B:
Hay Mark, I just realized it's been a while since I got back to you. I needed a way to calibrate the HP 5005A after changing the cabling to the TIMING POD, it calls for a 2ns or faster signal with the ability to add +/- offset, I had nothing that would do this. So, I acquired an HP 8007B pulse generator, it appears to function but has some issues I have been spending my time studying the manual for this as well as the HP 5005A.The HP 8007B manual from Keysight is barely readable. I have A HP one coming. I'm pressed for time; I only have until Sept. 8th. to either return or come up with an offer for a partial refund on the HP 8007B. It does what it supposed to do, Delay, Double Pulse, Amplitude, and Pulse width but not on every setting, I think it's transistor (switching) or Slide controls and not HP CHIPS. and it only goes down to 3ns. I think it just needs some Loven.
Then I will get back to the HP8116A and take up where you left off. I only have room on my bench for 1 of those large HP units at a time. Thanks for your patience and understanding. Just to clarify, I'm going back to the HP 8116A before working on the other 2 units. I just need to get the understanding & money out of the way.
MarkL:
I have limited bench space as well, so I'm familiar with the problem of one big thing at a time.
No rush on my part. Enjoy working on the other gear!
Mick B:
Hello Mark, it’s been awhile. I have read and reread the 8007B pulse gen. manual, and then read and reread it again. Perhaps you might be able to go through that with me when the HP 8116A is finished?
Back to the HP 8116A, I took up where we left off and here are the results.
I used the spring ground clip on TEST POINT 2 and resistor R265 coupled AC & DC. Otherwise, the ground is at the front of the power supply as before (PS ground). Please note the NAMES of the pictures and COUPLING.
These are photos of TEST POINT 2 leading up to R265, I’m not sure what to make of them AC/DC coupled? If anything, and the ridicules overshoot and preshoot. I checked readings starting at TEST POINT 2 and resistors R270, R271, and R265. I checked the AC coupling to see the voltage without all the offsets. It’s a lot of tweaking of the offset knob to get the wave on the screen large enough for readings
The overshoot starts out low at TEST POINT 2, right out of the VCO IC 201 then the overshoot and preshoot just go up from there. There is quite a bit of offset. This is as far as I got. I was thinking the voltage + and – 15V and + and 5V was to bias the amp and provide an output or at least 0V to 2.5V I think + polarity. But it is far from that as you can see. I think I should try and do a readjustment up to and including OFFSET adjustments, if nothing changes, I will open the one we just fixed and measure the voltage on that one (its trigger output is +2.6V @ 1.6% overshoot)
Wate!
IF THE VOLTAGE AT TEST POINT 2 IS NEG. HOW CAN IT TURN ON Q260 doesn’t it need +.7V to turn it on? I am confusing myself so much here seems wrong. Can you please enlighten me?
MarkL:
I'm a little confused where you placed the ground spring. I think you're saying TP2? But it doesn't reach anywhere near R265.
Or do you mean the ground spring was on a ground close by and you measured R265 and TP2 separately?
Ground is on one side of R265. So the ground spring would go on that side of R265 and the probe on the other side of R265. This would probe the trigger out signal. You can look for the trigger signal on one side or the other of R265 to determine which side is ground. Or look on the bottom. I don't have my unit disassembled at the moment to be able to tell you which side.
Place a 50R terminator on the trigger output on the front panel and then look at the signal across R265. We need the extremely short ground because the trigger out signal has a fast rise and fall time, and we're trying to figure out if the overshoot is actually coming from the trigger output circuit. The signal should be a square wave approximately 0V to +2.5V.
On the scope traces, "1_ TEST POINT 2 Spring gnd AC coupled.jpg" and "1_ TEST POINT 2 Spring gnd DC coupled.jpg"... That's an odd result for the waveform across R265. It shouldn't be negative. Was the ground spring on the grounded side of R265?
To be sure we're talking about the right thing, below is a photo of a ground spring. Sorry if this is obvious, but your post has left me a little confused. I should also mention that because this is an exposed ground, you need to be extra careful poking around with it hanging off the probe. Some probes come with small plastic sleeves that fit over the spring to reduce the exposed metal. (Mine don't, and I have accidentally melted/welded more than one spring.)
An alternative is to use a differential probe, which is much safer. But you would need a fast one to capture this overshoot event of 10-20ns (like 500MHz or more), and of course that functionality doesn't come cheap.
I would like to figure out the trigger output overshoot and then move back to the main output. I know it's a side issue, but I'm not totally convinced the overshoot is really there (e.g., could be introduced by probing, cabling, termination, etc.). This all was trying to get to bottom of it.
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