5973 Heater Error, "Muxed ADC error"(6144)

[benhutcherson]

I have a 6890-5973 system that I brought back to life a few years ago, and have only used intermittently.

I cleaned the source a few weeks ago, and wasn't happy with the sensitivity(plus apparently I'd had an airleak somewhere along the way as all the stainless was oxidized brown...) so spent some time with a Dremel/jeweler's rouge and micromesh following the SIS cleaning instructions. I'll also mention that the source heater block fell out(I stupidly hadn't realized it was removable) while I was cleaning, and I reinstalled and snugged up the set screw.

For reference, this is a first generation HP-branded system. When I first brought it back to life, it was still on HPIB. I had Geoff Wilson with Great Lakes Scientific come in and do a LAN conversion(he installs a SmartCard III and does some sheet metal work on the EMOD to allow access to the port, then fits a JetDirect card to the GC) and it is running on G1701EA. If it has any relevance, this is a diffusion pump instrument.

After cleaning last week, I did a pump down as normal. I was monitoring the pressures while it heated up, and would sporadically get 2048 "Temperature control fault". It finally settled down and I thought it was fine so left it over the weekend.

I come in this morning to try and tune it, and find that I was now getting a "no heater voltage" error, which as per the troubleshooting guide is a blown fuse somewhere(guessing buried down in the EMOD/mainboard? I don't see anything obvious on the side board).

I did a quick vent, power down, and popped the door open just to double check my heater and temperature sensor connections. I reseated all of them just to be sure.

Now I'm getting 2048 "Temperature Control Fault" again along with a new error message "Muxed ADC error"(6144). No, that's not a typo-Chemstation does say "Muxed"

I have gone through multiple power cycles hoping that would clear it.

Does anyone have any insight or possible troubleshooting avenues? I don't have a voltmeter here but am planning on bringing one from home tomorrow to check the resistance on the source and quad heaters. Aside from this, I don't know where to go.

[benhutcherson]

I called and talked to Geoff this afternoon on the way home from work.

He suggested first checking the fuses on the mainboard and also checking resistance on the heaters and temperature sensors(should be around ~100Ω at RT).

He then went on to say that it could throw the Mux ADC error if one of the temp sensors wasn't tracking with what the system was telling it to do-i.e. if it was heating and the sensor wasn't sensing a rise in temperature, the system COULD interpret that as the ADC being bad(if I understood him correctly).

Of course if all of the above checks out, he said it's likely a mainboard, but we'll see.

[James_Ball]

We had the Mux ADC error on a 6890 that had main board problems controlling the inlet temperatures. Could be something on the main board of the 5973 I would guess. Also there are some fuses on the power board if I remember correctly.

[benhutcherson]

Checking the mainboard fuses is on my to-do list.

I did get a chance to check the heater resistance this morning. The source heater is around 20Ω and the quad heater around 10Ω. Geoff said off-hand that they should be about 100Ω, but I can't seem to find this spec published anywhere.

Does anyone know what it should be?

[benhutcherson]

Never mind-looks like I'm pretty much in spec(if a tiny bit high)

https://www.agilent.com/cs/library/trou ... Points.pdf

[benhutcherson]

And pulled it open to find both fuses on the mainboard blown. I didn't need a VOM for that either-they were visibly blown.

I have more ordered and on the way-my big concern is what happened to cause them to blow. I keep thinking that MAYBE I shorted the source heater pins the last time I put it together(they are bent a bit) but I can't make enough sense of what should be going on to know if that would be reason for both the fuses to blow.

[benhutcherson]

I did some diagnostics on my own today, and then some over the phone with Geoff.

Long and short of it is it seems as though the instrument has lost the ability to toggle the source heater off. After I replaced the fuses, I powered it up and noticed that during pumpdown, the source temperature was rising even while my foreline pressure was still ~500mtorr, or in other words too high even for the diff pump to get turned on(which doesn't trigger AFAIK until foreline pressure is below 300mtorr).

It continued heating during pumpdown, which of course is an additional anomoly-as I'm sure those of you who run Agilent GC-MSs know(and I don't think this is atypical) the source and quad heaters aren't normally triggered on until hi-vac ready status is reached(diff pump hot or turbo at 80% or whatever they've set the threshold at). In my case the temperature continued on up to 300º, which should have triggered thermal shut-down but didn't. Manually setting the temperature setpoints to 0, which should trigger off, still saw temperature rising.

BTW, I verified that this temperature was "real" and not just a sensor error in a few ways. The first was that unplugging the gray cable, which is filament and heater power, saw temperature slowly go down. Second was that temperature tracked when I swapped the source and quad sensor connections. Third was that the source was physically quite hot-over 150ºC by the time I opened the vac chamber per an IR thermometer and hot to touch-even after venting.

Geoff had me run through a bunch of additional diagnostics and check voltage and continuity.

At this point the only reasonable conclusion we can make is that I'm going to need a mainboard as obviously I can't operate the instrument with no ability to control the source temperature-that is unless anyone else has any other insight on it.

Of note also, one would assume that since there are two fuses associated with the heaters(F1 and F2 on the mainboard) and two heater circuits(source and quad) that one fuse would be control each circuit. Geoff had assumed that was the case also but had never had a reason to verify. I can't quite make sense of what's going on, but I could not shut off the source heater unless I pulled both fuses. F1 would shut off the quad heater and both pulled would shut off both heaters, but pulling only one of the two fuses would leave the source heater live. F1 also seems to be what triggers the Muxed ADC error that started all of this. Of note too is that at one point I'd inadvertently installed one of the blown fuses in F2, and didn't actually realize it until I looked closer at the fuse and realized it was blown. Geoff said that even though the 5973 came out while he was still with HP, the never made board schematics available for it as they did the 5971 and 72, so he couldn't definitively say what was going on with that.

So, that's where I am-currently waiting on a quote from Geoff for a board and then I can go and beg for money. I'm also inclined to replace the source heater cartridge in all of this-it's not exactly expensive and my fear is that there's some lingering issue in it(maybe an intermittent short) that may have caused all of this.

[James_Ball]

Maybe give Yiming a call at Astrascientific, he does board diagnostics and repairs for us from time to time.

Astra Scientific <service@astrasci.com>

[benhutcherson]

Maybe give Yiming a call at Astrascientific, he does board diagnostics and repairs for us from time to time.

Astra Scientific <service@astrasci.com>

Thanks! Worth a try. I ran across their board repair service on Ebay for I think $1450 for this board.

I'll see what Geoff comes back with on the replacement cost and where that falls.

If nothing else, too, Agilent at least lists the board as in stock for $4500...

Hopefully this wouldn't be a crazy diagnosis/fix, though, given that the instrument is otherwise fully functional with this mainboard.

[benhutcherson]

Wanted to follow up a big since I left this one hanging.

First of all, for those of you who have worked with/been customers of Geoff and don't know this, be advised that Great Lakes Scientific will cease to exist at the end of this year. Geoff is merging with Resolution Labs out of Indiana(roughly West Lafayette/Purdue area). He told me he is eying retirement in a few years, but will be remaining with Resolution for the next 3 years as a full time employee and says he will probably still continue working some after that.

I'm happy for Geoff that he has a path toward retirement, and Resolution seems like a great company. They have a few more people than just Geoff and his daughter running the show, but are not huge by any means.

Geoff didn't have a board for me, but Resolution did and I'm currently working on getting it from them. Even though I know I'm capable of installing, the people writing the check for me on this now want me to have someone from Resolution come install it, so I'll be going that route.

In the mean time, I seem to have gotten quite an education about how the 5973 heaters operate-it seems as though they both vary the voltage and the frequency in their operation. I'm anxious-before this is fixed-to stick a scope on it and see what exactly is going on. At this point why not-the more I know about these things, the better in my book!