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I found C149 and CR34 both shorted. With those parts out, the DXM70 board DC rails are no longer shorted. Haven't yet installed replacements. For use exclusively on nominal 120 VAC mains, does anyone think the boards need or benefit from 450 volt rated capacitors?

The offending capacitor from my board doesn't appear to have bulged or leaked. Smoking gun was toasted FR-4 around the diode attachment holes. Sometimes that happens on working designs that have poor cooling or insufficient component derating. That's a little snip from a full-board pdf file off a flatbed scanner, here in case anyone wants to carry on with reverse engineering. I experimented with Visio as a tool for reverse engineering. Took the flatbed scan and overlaid circles and rectangles, keyed by color, on various layers. Looks promising, and I already learned some practical details of half-bridge drivers etc.

The supply uses a PFC/boost converter system which increases the voltage to a few hundred volts, so the 450V cap is required.

Here are 2 good references:

Spellman power supply reference
http://www.spellmanhv.com/-/media/Files ... manual.pdf

How to terminate cables for low corona/leakage
http://www.spellmanhv.com/Technical-Res ... age-Cables

Those are great references, Andrew. Thanks for the pointers.

Speaking of group buys, how about some repair kits with the nickel-and-dime components that many of us found dead? If you have to order an individual item by mail, you can buy ten for about the same total money (after shipping charge).

As Peter said a while back, "The supply is conservatively laid out and the RTV is a good indication of vibration testing for harsh industrial environments. Honestly it would be a pleasure to work on if I had a schematic. So it’s just finding the hours to do a methodical investigation/repair with a budget of $100 for parts."

I don't think Cliff would mind if we continue to share notes about the bill of materials, and sourcing of replacement parts. Here's a piece of a schematic learned by inspection, as others here have done. So far un-reviewed. Who wants to draw the power path from AC input through PFC circuit (Q10 and Q6), so we can see if it matches my scribbles? Can't see the label on my RV2 without removing the part, which measures about 24 ohms at room temperature. Can't see the label (or even the ref des) of rectangular pink capacitor next to the main bridge rectifier.

Almost forgot to mention, I made a DC resistance model of the whole interface coming up from the DXM70N's basement level. If the fancy inverter and control board were totally dead, or missing, why not use the potted "basement unit" to make a dumb HV supply, substantially derated of course?

I replaced the blown IRFBG30 mosfet on my power supply board, but it still does not function. I checked all of the capacitors, and C149 has a slight bulge but has no continuity. Otherwise none of the components on the board appear damaged. Removing the fan revealed that there is only about 2V on the bus, which I assume should be 24V. Any ideas what could be causing this problem? Some kind of bad voltage regulator? All six red warning lights on the front panel light up and blink repeatedly, so some power is going somewhere.
The other supply functions properly and I was able to turn the voltage up to 28kV. Still working on making a CA11 connector.

Hey guys,
A few have emailed me on this one...

...I feel your pain on this...attached are a few sheets of the power section schematic. Below is copied from what I have been telling a few of you that have emailed me directly:

Re: C149: There is a history on this parts failure mode: It had to do with some applications, when keeping the DXM in standby, at elevated temps. I don't recall the details off the top of my head...but it had something to do with the PFC hiccupping at light loads, causing high ripple on the cap. Under elevated temps, and after years of operation, it would fail. I think you can replace it with a similar rated part, and in your application it will probably be fine.

I do see that many fusor guys have these DXM's off of eBay....a flurry of posts in the past week. This specific model X# has a particularly sorted past... to date we have shipped over 1,000 of these units to one customer for their food inspection system. We have wrestled with reliability issues early in the program due to our customer using these in a inadequately cooled cabinet. Ambient temperatures far exceeded the ratings of the supply. My guess is the customer has replaced many of the units in the field, and you guys are seeing these used, replaced units. Failures tending to be around the power semi's and in the HV section. (Some ceramic HV caps do not like high temps).

Your “X3547” l unit has some differences from the standard interface:

High Voltage Interlock: Pin 11 on J2 is the H.V. interlock in both local and remote mode. The hardware based dry contact closure must be closed in order to enable the high voltage via J2-15 in local mode or USB, Ethernet or RS232 mode. This can be done by connecting pins 11 and 12 on J2. The interlock must be closed prior to the unit being enabled. If the interlock is open and closed while the unit is enabled, the enable will need to be re-asserted to generate high voltage.

High Voltage Enable: Pin 15 of J2 is the H.V. enable for the local mode only. The hardware based dry contact closure must be closed to enable the high voltage. This can be done by connecting pins 12 and 15 of J2. This I/O is disregarded in remote mode.

Good Luck. Be safe.

Cliff, thanks again for the continued help you provide to the fusor.net community, I'm sure those pages will help a number of people debug their supplies. By the way, what is the -15v LVPS variable and what should it's normal value be(is this just the -15v DC bus voltage)? The manual also specifies that there are some test commands that you can send the supply, could you provide us with the syntax for these?

6.7 SPELLMAN TEST COMMANDS
 Program Hardware Version (Hardware setup)
 Program Model number(Hardware setup)
 Set USB Mode (Program USB)
 Set USB Page Address (Program USB)
 Send USB Page Data (Program USB)
 Toggle Passthrough Mode (Diagnostics)
 Store A/D Calibration Value (Hardware setup)
 Request Miscellaneous Analog Readbacks
Contact Spellman High Voltage for details and the syntax of these
commands.

Liam,
The IRFBG30 mosfet is part of a flyback converter that generates the 24V(first page of the schematic Cliff posted) that then is regulated down to all the lower voltages the supply requires. If you apply 24V to the fan connector this should power up all the digital circuitry/Ethernet interface for testing. If there is 2V on the fan connector when the supply plugged in I would suspect a problem in this flyback converter.
The converter draws power off of C149, what voltage do you have across this capacitor when the supply is plugged in?
Is the transformer primary ok(pins 3-4 on T2)?
Diode CR34 feeds voltage to C149, is the diode ok?

I applied 24V to the fan connector and the digital circuitry came on with a green system power light. This narrows the problem down to the converter. C149 has about 120V across it, diode CR34 is good, and the transformer T2 appears intact. Both secondary coils do have continuity between them, but I would assume this is because of other components. My suspicion would be that the UC3845 chip or the CL70 NTC thermistor is bad.

Check R206, if it is open the mosfet won't be sinking any current to ground.
Also check for an open in the traces between C149 positive and pin 4 of T2, the trace between pin3 of T2 and the mosfet, and the trace from the mosfet to R206.
Check voltage on pin7 of UC3845, it should be bootstrapped by the R192,R200,R197 resistor chain even if the boost converter is not working.

Does a relay click when you plug it in?

The relay does click when I plug it in. I will update this post tomorrow when I check the other components you listed.

To answer Andrews questions:

-15V: Uses a charge pump converter. See attached. Has a pretty high output impedance. Usually "-15V" can be in the -12.5- -14V range...ish.
See attached info on the other test commands.

Hip, hip, hooray for Cliff. Very generous of you to share those official schematic pages. And the story about those pesky C149's. Good to know that my employer isn't the only one who sometimes traces reliability issues to product abuse by customers.

The charge pump IC for -15V reminds me of a new-ish class of components possibly handy in fusor labs. They're called photovoltaic MOSFET drivers, e.g. APV1121S or VOM1271. You put in about 10 mA and get an isolated DC source of more than 8 volts (with s/c current in the low microamp range). We have a design with 4 in series for 30 volt power to some "high voltage" CMOS analog switches. Might be handy for biasing certain radiation detectors whose average current is negligible.

Does anyone have a pin identification diagram for the CA11 connector? Does anyone know the derivation of the letter codes for the pins?

The C,S,G etc are named in DXM manual somewhere, maybe even on short brochure which gives pinouts of all connectors.
Left two terminals are internally connected, and right two terminals are connected.
If you aren't using the filament supply, any single pin could be used for HV. No practical difference which side you choose.

I couldn't find the pin identifications in the DXM manual nor in the documents on the Claymount web page. I know they're all connected in the DXM in regard to the HV, but some people are planning to power a filament with these supplies. Does anyone know the historical derivation of what the letters stand for?

Just learned that S and L are for Small and Large filaments, and C is the "HV output" according to http://vjv.linx.netdna-cdn.com/wp-conte ... VG223k.pdf .
Same here from Spellman, in brochure for a line of bigger power supplies: Now when there are 4 terminals, what's the fourth one called?If the letter is G then I bet it's for Grid, aka focusing cup or Wehnelt electrode. Okonite, a cable mfg, says:
Cable Core: Each Low Noise cable core contains two insulated filament conductor. In 65, 75, and 100kV cable filament conductors are #15 AWG (19x) [1.65mm2] tinned copper insulated with heat sealed color coded polyester tape. ...
Four conductor cables include one #20 AWG (7x) [0.52mm2] copperweld conductor per ASTM B-45 insulated with heat sealed polyester and shielded with metalized red polyester.

[edit] OK, my money is down on the table.
Small filament
Large filament
Common to both filaments
Grid -- for beam focus, could be 100 or 200 V more negative than the filaments.

From an early post by Andrew S:

The CA11 pin list from the DXM data sheet is reproduced below along with the wiring diagram from the DXM manual. They recommend a Claymount L3 cable as listed, but it seems strange to state that the "bare shield wire" would be connected to the high voltage. I think they must be referring to the bare inner wire which is one of the three conductors and not to the outer braided shield. I checked an old full size federal connector (3 pin) cable I have, and the braided outer shield is indeed connected to the chassis ground part of the plug as one would expect, with one of the three pins connected to the bare wire inner conductor. It must be part of the X-ray cable jargon to refer to the bare inner conductor as the "bare shield wire."
I still have found no diagram that identifies the positions of the C, S, L, and G pins on the CA11 connector; i.e. the relation between the 1,2,3,4 on the drawing below and C,S,L,G.

I just looked again at Andrew's connector photo and noticed that he has the pins marked (the old eyes aren't what they used to be). So relating this to my drawing of the "CA11 socket":
1 = L
2 = G
3 = S
4 = C

Looks good, but I'd number the pins differently. Here's my take on it: A convention has persisted since vacuum tubes, including IC's in TO-cans, DIPs, etc., even modern packages smaller than vacuum tube pin diameters.
Pin numbering runs clockwise when viewing a socket from the wiring side, or a removable part from the pins side.
Counterclockwise when looking at a socket from the user side.

Ran Andrew's DXM test on my unit. The xray on light comes on momentarily followed by the over voltage light. Any ideas?

The over voltage light should come on at the end of the test when voltage set is set to 0V and the output voltage is still decaying(due to it's RC time constant, and no load resistor). This is normal operation if the over voltage light only comes on at the end. Before that the output voltage should be tracking the set voltage on the graph.

Does it make a graph?

A single blank graph with no plot briefly appears. Then two blank graphs appear together. The graphs all disappear and an error message is displayed. "Vectors must be the same length. Error in => Spellman_DXM_control.m at line 137"

I ran the functioning power supply with my fusor today and had some problems. I could turn the voltage up to 27kV, but plasma would not establish at any voltage around 15mtorr. Turning the voltage above 27kV got plasma to establish for a fraction of a second, but the over current light came on immediately and switched off the power. I use a 10-turn potentiometer to control the voltage and have the current set point at the max, but the over current light comes on regardless of how finely I turn the knob. Does anyone have any suggestions? I use a 6-way 2.75 conflat chamber, so Paschen's Law gives different values for my smaller chamber than the standard 6" chamber, but I've heard that other people with smaller chambers have had few problems in establishing plasma.

What value is your series limiting resistor in the HV feed???

It's a 60k resistor, and operating it with vs. without the resistor seems to have very little effect.