ENI OEM-6 RF Plasma Generator - Line voltage selection?

[torinwalker]

Gentlemen,

Recently acquired a used ENI OEM-6 13.56MHz RF Plasma Generator. I found the service manual at Arizona university, but it doesn't detail the line voltage selection. I'm wondering if any of you are familiar enough with this unit to know how to configure?

Inside at the rear left over the power supply, there is a Molex terminal block with four 10 or 12awg taps from the power transformer, and on the other side, a wee little 22awg wire connected to one of the terminals (originally 208V). I've set it to 240V, but my instinct tells me this wire is way to thin to carry the current for the entire (600W) generator and that there must be something else required to set it up properly. ... but I don't have a manual to tell me otherwise.

So, does anyone have the manual for this unit? I don't need a copy, unless you're offering, but perhaps you could you tell me if this is the only location where the power selection is made.

I've tried reading manuals for similar ENI products (wideband amps, for example) but they're all too different to be of any help.

[torinwalker]

This is turning out to be an adventure.

Line in -> line filter -> single-phase contactor -> transformer -> pair of rectifiers -> capacitor bank -> RF section.

That wire BTW was 18awg, not 22awg.

Broke it down section by section and verified line filter ok, contactor energizes ok, transformer windings not shorted nor open and winding resistance at each tap measuring proportionally to voltages. Removed capacitors and verified all good, then narrowed it down to the regulators. Desoldered regulators and verified LV side of transformer also good. Tested the rectifiers: One of two rectifiers that had two diodes shorted to ground, and the other rectifier had one diode on the verge of failure (read different, lower forward voltage than all the rest.) That's why the fuses were blowing. Replaced them both with new ones from Amazon and the unit powered up.

Now the problem is on the RF side of the house.

RF power light comes on when RF switch is activated, but won't show output on the meter. When I get to 5% (0.05 on the ten-turn vernier POT), the "Max Power" light comes on. Despite keeping it below that threshold (26W or about 0.04 on the poteniometer) the RF section still won't produce a signal - not getting any waveform on the oscilloscope, nor does it move the RF power meter into a dummy load.

Now tracing the RF module's controller board to figure out why no signal is being generated. The yellow LED off of Q1 isn't being lit, so have to assume something wrong with an interlock, or otherwise the unit's power-overload circuitry is blocking output to the driver-amplifier stage. No 3mV signal from the SMC output connector on the control board, so waiting on schematics so I can trace the control board.

Anyone on EEVblog ever work for ENI? Would be nice to talk shop with someone who has worked with these OEM units. The president of E&I (new name for the old company) says OEM's didn't get carried over in the new product lineup, so no help there.


Torin...

[coppercone2]

so the power rails have the correct voltage?

You can measure quiescent current to see if there is a shorted subcircuit that is current limited.

I had a similar problem with a limiter on a voltage/current calibrator. One polarity would work, but the other polarity would trip OVL at a volt or so.

I found corrosion in my unit, wicked up a wire... but no batteries in there. not sure what the hell was wicked on it.

But I started to find some other stuff, that was quite evil. A ring lug that was broken and attached to a transistor. Like the crimp wire junction was OK, but the crimp literarly split in half, and it was pressed under plastic. So if you did a continuity test between the end of the cable harness, and the exposed part of the ring lug, not under the transistor housing, it was OK. But if you gave it a tiny yank, you would see that the crimp split under where the screw was (the smaller then to-3 package). The transistor plastic cover held the ring terminal in place, but the ring terminal was not making contact with the transistor anymore. !

 On a ring lug for the main output transistors. Some how this was part of the reason for a early OVP fault. Because it had a cable harness that went to the transistors on the back attached to a heatsink outside of the chassis with a cover to protect against touch.

Now thats DC vs RF, but similar behavior. But I threw my unit out because the wafer switches were like deformed into the PCB and I could not desolder them, plus I had enough dealing with corrosion damage that year.

[torinwalker]

I have traced the problem further back to a voltage regulator board that takes 44VDC unreg from the power supply side and converts it to 25VDC through an "ENI-1B" power transistor (still trying to discover the spec on this custom transistor), then on to the driver preamplifier board. According to one service manual (not the correct one, which is still on its way), I should be getting 25VDC from this regulator board. Instead, I am getting 0.5VDC which is probably why the controller board isn't bothering to create a signal. Won't know what the LED is for until I get the schematic, but I believe it lights when Q1 is driven, which would indicate RF power. No LED, no RF power... but I didn't need the LED to know that.

I am narrowing in on a potential replacement transistor. My best candidate so far is an MJ15004, but waiting on a variety of unlikely sources to confirm.

I'm tempted to apply 25VDC from my power supply to see what happens, but there is another brown wire that I don't know what it does, so again... waiting for the proper schematic which should arrive by Friday next week.

The regulator board is in an awkward spot - it's in the middle of the RF section, and divided between two parts - the circuit holding all the supporting electronics (various resistors, diodes, caps, and biasing transistors) and an aluminum mount through which the ENI-1B is mounted. Because the transistor leads pass through the aluminum mount and solder to the board, and given that the board is mounted to the aluminum mount, it makes for a helluva time examing the regulator board. I'm trying to verify components in situ, and so far most things check out except for one resistor that seems to be lower than its printed value.

Ideally, if I could see everything properly and not be staring down a thin gap between the solder-side of the board and the aluminum mount, I would simple recreate a schematic. Instead, I'll just wait for the real schematic to arrive.

Meanwhile, my biggest problem now seems to be identifying this "Motorola ENI-1B" custom transistor. The four owners who left ENI after MKS bought them to start up "E&I", aren't forthcoming with information. So now I'm on ON-Semi's support forum hoping someone might recognize the transistor based on a photograph of the die (the only information other than the label that I can provide.)

It looks very similar to an MJ15004 power transistor, but I'm not confident enough to just replace the existing transistor. Not yet, anyway.

To answer your question, yes power rail (+44-48VDC from the unregulated DC supply - the only rail provided supplied) is, more or less, it's within the range. I'm in Canada, so our grid runs at 247VAC which translates the specified 44-48VDC up to 45.4 ~ 49.4VDC, so it's at the high end of the +/-5% range but reasonably within spec (under load I would expect this to drop closer to the service manual spec.)

One more little item, but one of the two LM317T's that supposed to provide +15DC and -15VDC on the control board is actually producing +14ish and -12.8ish, so the latter might need a new LM317T as well, but one step at a time.

Once I get the schematic, I'll be in a better position to undertstand what's going on and to know what to measure for, and I will look for that quiescent current you're talking about.

[coppercone2]

the 12.8 sounds a little suspicious. are you sure thats not a minor short? check currents to see if they are reasonable IMO

[torinwalker]

Good catch. I figured I'd just replace the LM317T, but you're right. I'll trace around and see if I can follow it to some other component that may have shorted.

Incidentally, I traced the entire circuit and recreated the schematic, then ran it through a simulator using the closest power transistor I could find to replace the ENI-1B, an MJ15003. Sure enough, the circuit simulates 25V out when the RF switch is closed (R14 = 0 ohms), and... get this: about a 1/2 volt when the switch is open (R14 = 100G ohms). Plus, when I measured the transistor I was getting 0.46V between base and emitter, and about 0.445 ( a little low, but still nearly a diode drop) between base and collector. So, I think it's behaving normally and the fault probably lies elsewhere.

Gotta keep hunting.

[coppercone2]

well thats a powerful technique to deal with unknown parts

[coppercone2]

and I have seen many drifted base transistors. in pretty much everything, including RF amp.

with carbon composition I basically expect that the gate resistor for the power transistor will be drifted, I usually replace them all with metal oxide. IDK if the frequency for this thing is too high for metal oxide. Ceramic composition is 10% and expensive. Might be worth taking a gamble at that for a nice ENI unit though, those things are kinda epic

Like the composition resistors <20 ohm near the power transistors seem to be off by even 30%. not sure if that is where you found that resistor, but I feel if its near some power transistor thats expected

and yes those heat sink under PCB things are screamers I usually replace things there for good measure if I have any doubt because its painful to trouble shoot that. like holy shit that is annoying. anthrax power supplies always do that, but at least they have sockets! big ass heat sink covering the entire PCB bottom so you are peering through a slit for hours like some creepy pervert. by the time that is open and i start to imagine the possibilities I start replacing things indescrimately.

also be really careful closing that because what happens is some god damn standoff that is press fit in there will fall out and you forget about it and then you try to tighten a heat sink and you get a unexpected ground short some where on a slightly bowed PCB.

[torinwalker]

It's DC. It's converting 44VDC from the unregulated transformer/rectifier/capacitor bank to regulated 25VDC so it can drive the preamp board. The preamp has three RF transistors, the middle stage is driven by this regulator board, and the final stage is driven directly by the power supply's 44VDC.

I received my schematics, finally, then had to take off for a conference in Vegas. But I'm back now and can concentrate on the generator again.

The schematic I drew was practically identical to the schematic in the manual, except their caps next to Q1 and Q2 were drawn connecting straight to ground. I've redrawn mine to be the same. I even guessed the zeners correctly in spite of not being able to see one of the part numbers. I used MJ15003 in the model, figuring that's about as close of a guess to the ENI-1B as I could figure. In the schematic, they've replaced ENI-1B with a TIP35C (TO247, 25A and 125W). So, this gives me further confidence that my simulation should be correct - ~0.45V when the RF power switch (simulated by R14) is off, and 25V when it is on. I think I need to run over everything again to make sure I'm measuring correctly. At least now I know that the 44V goes out to the front panel and back in to the base of Q1, so this should turn on Q2->Q3->Q4 @ 25V. If it doesn't, then I'm back to diagnosing this regulator board.

The case of both Q4 (the power transistor) and Q1 were showing only a few dozen ohms to ground. Figuring there was a short, I desoldered Q1 and tested it. It tests just fine. Good thing, because they're $30 each to replace.
After removing Q1, I tested Q4 (in circuit) which proves to be an NPN, not a PNP as I had always suspected. Q4 appears to be working; base to emitter is .46V, but base to collector is only 0.44V which is a little lower than the 0.45 ~ 0.9V suggested by some blog I read, but I figure close enough to a diode drop (probably perterbed by other components in parallel, since I couldn't remove Q4 to isolate it - or maybe it's this drift you're talking about?) Anyway, I found an ENI-1B transistor on eBay in England (18 pounds + shipping), which I'll keep in mind in case this one turns out to be faulty after all.

Before I left for the conference, I soldered Q1 back in place, remounted one of the amplifier board covering Q4's heat sink (which I never was able to remove), and will power it back on again and start looking at that voltage regulator that should be -15 but is actually -12.8. I'll start looking for that potential ground short on the controller board. I'll also test for base resistor drift in the regulator.

[torinwalker]

UPDATE:

I got it working. Unfortunately, I can't say what it is that finally caused it to work.

It seems that in the process of taking the entire unit apart, disconnecting the multi-pin connectors, desoldering one of the transistors from the regulator board (to test the transistor), then resoldering it back in and reassembling the entire unit... it suddenly started working.

Potential suspects:

• Removing and reseating the screws holding in the power transistor may have changed how the regulator board was grounded.
• Desoldering/testing/resoldering Q3 may have done something, but I seriously doubt it.
• Taking out the RF section to test the thermostat on the underside, which required detaching/re-attaching (re-plugging) wire connectors may have caused them to regain contact?
• Shaking the entire thing upside down to remove a piece of copper desoldering braid I thought had been flung into the chassis accidentally...
• Disconnecting and reconnecting the front panel wire connectors multiple times...

Whatever the hell I did, the unit now powers on and shows output power climbing on the meter as I crank up the RF power out potentiometer.

Fantastic. And I'm glad I didn't have to replace that ENI-1B power transistor, because I still can't find a suitable replacement.

Finally, thank you, coppercone2, for tagging along on my journey and offering sensible advice. Our discussions are greatly appreciated.

I'm not out of the woods yet. I hooked up my power meter and dummy load and saw it produce about 100W before the overhead LED kicked in. Just need to sanity-check that the output matches the power meter, verify SWR, and maybe calibrate per the service manual.

Torin...

[coppercone2]

pfft it could be a cracked solder joint that only shows up when the board is installed and no pressure is on it. i have seen that with a socket that was sensitive to position of equipment (sideways worked). waste of time to try to figure out what it was until it comes back. or the open circuit near a transformer on HP that when you probe it disappears!

For the transistor screws, I always take em all out and do ultrasonic on them and then grease or replace if corroded. But I did notice that if you put cold gun blue on screws, they still conduct pretty good (do this for exterior chassis screws). But I also dip em in molten deoxit so it gets a layer to prevent corrosion.

if you want to wait 6 months to 2 years, deoxit will show invisible corrosion on some parts after long term exposure too with green growth. With connectors look under magnification too.


BUt from experience, resocketing cable harnesses never did much for me for test equipment. usually it seems to be a solder joint. Different story for consumer equipment. the cables for test equipment seem to be better quality.

you could also have a cracked via or rivet that is not filled with solder totally that made a hairline fracture you sealed when you resolder the parts.

reflowing the solder on connectors might be  good idea too. because usually you have brass being soldered there, I feel like its easier to mess up a connector solder joint then it is to mess up a component solder joint, and they are rushed in the factory and might have a underpowered iron (common for them to try to make you use the same iron tip even, for small resistor and power connector, because it takes too much time to switch tips and they don wanna buy a bigger iron. With modern tool its less of a problem if you get the quick snap fit soldering iron tip but its still factory workers you are talking about, they aint getting nothing for doing the job better, only faster.

with 6 months experience I experience someone using a 0.7mm cone tip to solder ground plane



and if its not gold plated its suspect. I should mean to say I never had much luck from resocketing gold plated connectors. old tin is a different story.

I been meaning to try to figure out if a dilute HCl bath (a few percent) for carefully dipping tin crimps into will clean them up. I got liquid tin recently and I am impressed with the performance. I feel like it might be able to restore tin plated connectors. Just need to dip super carefully so it does not get in the wire (lowering jig)

but if it works i kinda recommend against doing too much because the last ting you want to do is lift a good trace resoldering something you dont know is bad. good way to ruin a weekend

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but specifically what comes to mind is cracked trace under the transistor screw you reseated. when you reseat the screw maybe it preturb the trace and bridge it. that is a likely area for copper to crack (possibly nearby). might be worth while to look at the area within a 2x2 inch radius under magnification to look for cracks

[torinwalker]

All good points regarding reflowing solder to fix cracks in the traces. I never thought to look... but then again, it was super-cramped in there between the back of the PCB where the traces are and the transistor heat-sink, which is spaced less than a 1/2 inch from the board.

So, I will keep this in mind when and if the generator fails again. Now that it's up and running, I need to run some more tests to make sure it's putting out power relative to the meter setting, and the VSWR reflected power shows zero even though my external power meter is showing reflection - I think a calibration will be necessary. It looks like someone was playing with several of the pots on the control board, though none related to VSWR... just another puzzle to solve, I guess. I'll post more later once I get into the calibration.

After that, next step is to build a little plasma sputtering gun (Ben Krasnow from Applied Science youtube channel demonstrated one he built himself, so I'll remake one like that) and get this new-to-me Maxtek thickness monitor running just as soon as I receive the matching oscillator. The TM is another eBay crap-shoot - a unit listed as "parts or not working", but whose description gave me the impression that it will probably work if the oscillator is connected. Let's hope my instincts are correct and this thickness monitor isn't DOA as well.


Torin...