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That's right, Harvey! Thanks!

On Mon, Feb 5, 2024 at 2:37?AM Harvey White <madyn@...> wrote:

I don't think he wants IDC connectors, as perhaps handy as they may be.
I think he wants to solder bare wires to the board, and is looking for a
method to strip the whole cable (whatever width) for about 1/8 of an
inch or so to enable soldering.

Harvey


On 2/4/2024 8:12 PM, SCMenasian wrote:

If your cable is the type I think it is, you don't need a special tool if you have the correct connectors.
3M made (makes?) the flat cable and connectors. The cable I used has 0.050" wire spacing and you cut it off to the desired length. It is, then, inserted into the connector which, when pressed shut, makes all the connections simultaneously. They made tools to do this but you really don't need the tool. An ordinary vise can be used to squeeze the connector and make the connections. many manufacturers make the cable and connectors. Look up, in digikey:
Product Index
Connectors, Interconnects
Rectangular Connectors
Board In, Direct Wire to Board

I'm planning to at least create a high-voltage probe to measure HV voltages and maybe even try to fix them when I learn more about safely working with HV.

As observed, FRAMs may work but when they don't, the reason is usually
attributed to the fact that the CE pin needs to be toggled for each write in
many popular FRAMs whereas in the Tek scope it is held steady. However there
IS at least one FRAM which does not need CE to be toggled and that is
PM28V020. From the datasheet:

"The FM28V020 is designed to be a drop-in replacement for standard
asynchronous SRAMs. The device does not require CE to toggle for each new
address. CE may remain LOW indefinitely while VDD is applied."

Not sure if it is the only potential issue. FWIW I tried it in my 2465A and it
works.

Best - Ram

I don't think he wants IDC connectors, as perhaps handy as they may be.
I think he wants to solder bare wires to the board, and is looking for a
method to strip the whole cable (whatever width) for about 1/8 of an
inch or so to enable soldering.

Harvey


On 2/4/2024 8:12 PM, SCMenasian wrote:

If your cable is the type I think it is, you don't need a special tool if you have the correct connectors.
3M made (makes?) the flat cable and connectors. The cable I used has 0.050" wire spacing and you cut it off to the desired length. It is, then, inserted into the connector which, when pressed shut, makes all the connections simultaneously. They made tools to do this but you really don't need the tool. An ordinary vise can be used to squeeze the connector and make the connections. many manufacturers make the cable and connectors. Look up, in digikey:
Product Index
Connectors, Interconnects
Rectangular Connectors
Board In, Direct Wire to Board

I did a lot of side-by-side comparisons and found something that I cannot
explain. The base of Q32115 is fed from +17V through R32117, a 120k. If I
check across that resistor in circuit, it checks at 114 ohms. Thinking it
could have drifted low, I lifted one leg and it checks at 118 ohms. Not spot
on but at least in tolerance. The base resistor for Q3285, R4377, another 120k
ohm, checks low in-circuit the same way as R32117. I haven't lifted a leg on
that one to see if it may be low but I plan to do that.

I don't know if that could have anything to do with the instability going on in
the -50V circuit but it seems rather wrong and I can't explain why.

Thanks,
Barry - N4BUQ

I FOUND IT.

C32119 was the culprit. I had a 0.01uF ceramic handy and when I placed it
across C32119, the scope came to life. I then clipped a 0.0033uF in parallel
with it and it still worked perfectly. I desoldered the existing cap and
placed the 0.0033uF in the holes (I didn't solder it in place as I'd like to
get a 0.0022uF to stick with the book) and that also worked.

Now that I had it out of the circuit, I tested the old cap and, oddly, it tested
very close to 0.0022uF. That made me really wonder what was going on so I
stuck it back in the holes and it didn't work - at least not right away. I
wiggled it a bit and could get the scope to work but I think it would still go
haywire when I pressed the BEAM FINDER. I don't know but it could have
something to do with the way the leads were bent because before I tested it, I
straightened the leads so it would fit better in the ZIF socket. Still, I
think it's flaky.

I want to thank everyone who has given me help and suggestions. I probably
should apologize to the list for droning on about this because several weeks
ago, Prof. Lee had suggested I do exactly what I did tonight and, if I had, it
would have saved a lot of "bandwidth". Ed's email earlier today further pushed
me to look at those caps again and I'm glad he did. Thanks also to Harvey,
Mark, Renée, Dave, G?ran, Renaud. John, and Andreas (and, out of 133 messages,
probably others that I'm missing) for the responses and suggestions.

Barry - N4BUQ

Hi Ed,

Thank you SO MUCH for that analysis.

C32119 was one of the first suspects and I need to go ahead and look at either
replacing it or adding some capacitance in parallel with it. I really hadn't
considered C32134 very much at all but perhaps I don't need to cross it off too
quickly. I've replaced C32141 and C3289 to no avail and, truthfully, I didn't
much expect it would. C32119 and C3278 might have much more effect than either
of C32141 or C3289. I believe C32119 and C32134 are both the boxed values in
both regulator boards.

I wasn't considering the extra load on the -50V supply when the BEAM FINDER is
pressed but, if so, then that would make more sense. I was thinking that the
small changes on the -15V supply when that was pressed was possibly the
triggering event but maybe not.

I plan to swap back in the original board and try some of the things you've
suggested as that's a fairly easy thing to do now. I'll report back what I
find.

Thank you again,
Barry - N4BUQ

I looked up the manual, and I think the -50V regulator is marginally stable.
Your observations about relation to the approx 200 mV drop on the current sense
resistor, and the clue that the beam-finder trips it too, indicate that when
the DC load is low enough, the overall open-loop voltage gain rises enough to
go unstable. When the beam-finder is activated, the deflection amplifiers have
marked change in gain, which also reflects in the -50V load current (likely
goes down). Once oscillation starts, the DC bias levels throughout the
regulator loop may change enough form a bi-stable system, which could explain
having to shut it down to reset it.

I'd suggest doing some experiments to swamp the HF gain, mostly in the output
Darlington pair Q32143 and Q32139. Note that in the +50V supply, there are only
two voltage gain stages, while in the -50V one, there are three - the last
being the Darlington operating in common-emitter mode, versus the one in the
+50V being an emitter follower only. The various scaling for the regulation
voltages and stages should make their overall gains roughly the same, but the
extra stage might make it more sensitive to part variations in the minus
supply.

There are some spots where compensation is done, namely involving C32119,
C32134, and C32141. Note that C32119 and C32134 are "boxed" (at least in the
manual version I found), indicating that the values or parts were changed at
some points, or may be selected. Note that in the -15V regulator, C3278 is also
boxed. It has the same topology as the -50V one, so similar issues due to that
"extra" gain stage. The positive regulators all use the same type, with NPN
emitter follower output, and no boxing of the compensation caps. To have the
same (symmetric) topology, negative supplies would normally want PNPs for the
output, but in many designs, the NPN circuits are used for various reasons like
making all the same part etc. This is very common in Tek, HP, and other designs
- HP has some very strange arrangements including stacking raw supplies on top
of ground-referenced pass transistors, for instance.

Anyway, it's not a bad thing, but it makes it a little more complicated to
compensate and handle part variations. Again, the boxed parts in the minus
regulators here indicate that changes have been needed. So, you may want to box
certain ones yourself to custom-fix the unit. First though, you'd want to
verify the (in)stability situation, by grossly swamping things out to see what
happens. You could try upping the value of those caps mentioned - not by
extreme amounts, but say maybe two up to ten times, by tacking in extra caps in
parallel (not replacing). I'd start with C32141, since it's the one most
associated with the extra gain. You could try a brute force approach putting a
Miller C (C-B) right on Q32139, but it could be tricky since the base impedance
is very low, so the C could need to be pretty big. Swamping it here would come
close to simulating a slower transistor in this spot, without actually changing
the part. Next I would look at C32119, and lastly C32134. With all this sort of
stuff you have to be careful to not go too far, or it could aggravate the
oscillation instead. The main thing is to see if simple small changes can get
you enough phase margin. I would think so.

I think with some experiments you can figure out a workable fix. Good luck.

Ed

On Fri, Feb 2, 2024 at 11:07 AM, Tom Lee wrote:

The "tail end" is the snap interval. In equation form, trr = ts + tsnap.

Okay, now that I've read Tom's replies, as well as the Wikipedia article and part of Boff's paper, I THINK I'm up to speed. One final question:

Is Tsnap equal to the width (duration) of the resulting pulse? (I assume it is, but that's never been stated explicitly.)

thanks

If your cable is the type I think it is, you don't need a special tool if you have the correct connectors.
3M made (makes?) the flat cable and connectors. The cable I used has 0.050" wire spacing and you cut it off to the desired length. It is, then, inserted into the connector which, when pressed shut, makes all the connections simultaneously. They made tools to do this but you really don't need the tool. An ordinary vise can be used to squeeze the connector and make the connections. many manufacturers make the cable and connectors. Look up, in digikey:
Product Index
Connectors, Interconnects
Rectangular Connectors
Board In, Direct Wire to Board

The connector is already decided, it is the PCIE x1 connector. All I
need to figure out is how to solder a ribbon to a pcb with minimal
effort and cost and rejects, and how to house the whole thing (pcb +
ribbon) in a cartridge-style enclosure.

On Sat, Feb 3, 2024 at 8:04?PM Jared Cabot via groups.io
<jaredcabot@...> wrote:

I would be looking at IDC connectors, like what was used on old PATA hard

disk drives, or FFC/FPC cables and connectors.

The former is bulkier but can carry more current and endure more flexing.
The second is more delicate but is much lower profile.

The FFC cable could feasibly be soldered directly to the PCB if you want to

forgo using connectors.

Also, thr male side of the IDC connection could be edge mounted at a stretch

to make things lower profile than a 90deg connector, depending what your fab
house is willing to fiddle with.

Jared