HP/Agilent 5890 Warning: Oven Shut off

[juliandev]

Hi everyone,
A long time running HP 5890 Series II (120V Version) GC with ECD detector recently started reporting: “Warning: Oven shut off “ on the interface front display.
None of the heated zones (oven, detector, custom built detector enclosure) gets heated up, nor does the GC oven fan operate. At the same time, we can’t power up 2 auxiliaries (a 120 V vacuum pump, and a 120 V solenoid valve), which are connected to aux 1 & 2 (purge valve 1 & purge valve 2) via the J14 Connector on the main board.

Other parts of the instrument seem to work fine:
Self Test on start up is successful.
Temperature readings from all the heated zones are provided.
Checking the 5V, 15V and 24V test points on the Main board was successful.

According to HP’s service manual, we checked the power supply’s PCB- as well as the main board for blown fuses – couldn’t find any
We checked the resistance of the GC oven heating coil – it’s good.
We found a replacement power supply PCB and swapped it in – same errors.
We found a replacement transformer and swapped it in – same errors.

We suspect that all 120V (i.e. the power for the oven fan) don’t get properly fed, in contrast to the lower voltage ones.
We were wondering for probable causes.
Any advice or hint on how to further constrain the error would be much appreciated.

Best Regards
Julian

[Bigbear]

There is a triac just after the main power input to the GC, I had one blow and had the same symptoms as you. Get in touch with Alpha Omega Tech. they should be ale to help you.

[uzman]

Did you check the door switch ? If the door switch is not closed properly or if the switch is faulty , it may cause this error.

[juliandev]

There is a triac just after the main power input to the GC, I had one blow and had the same symptoms as you. Get in touch with Alpha Omega Tech. they should be ale to help you.

thanks for your advice, it's good to know that this is fixable.
Just to be sure, are you talking about the one single triac sitting in the lower back of the instrument, where also the mains line enters, close to the AC PCB board and connected to it via P5-P7 ?
Or are you talking about the whole row of triacs which are sitting on the main board of the instrument?

I checked the single triac in the back quite rudimentary (shorting it with a screwdriver and measure resistances between MT1 & MT2), and this test suggest it's fine. Get readings of 50 Ohms between MT1 & G as well as between MT1 & G/MT2 short.

What did you end up replacing?
Thanks for your time and help
Julian

[juliandev]

Did you check the door switch ? If the door switch is not closed properly or if the switch is faulty , it may cause this error.

It came to my mind and I had a look at it. However I couldn't think of a sophisticated way to check its functionality. Do you have a idea?
Optical impression is good and it gives a reassuring click sound when i close the door shut.

The problem occured during a time, when the oven door wasn't opened or shut.

Thanks for your time and help!
julian

[uzman]

If I remember correctly , there is also a upper temperature safety sensor inside the oven.
This sensor is connected series to the triac control .

[juliandev]

Thanks for the helpful answers.
The thermocouples seem to work since the temperature readings fluctuate around room temperature. Hence, I doubt that the maximum value is reached and power is shut off.

We exchanged the 600V 35A Triac in the back of the instrument (close to Power Board and Mains line).

Same issues

[osp001]

On page 1-7 of the service manual, it is suggested that another cause of WARN: OVEN SHUT OFF is a stuck oven flap.

If that's not it, perhaps reinvestigate the oven door switch. Get on in there with the VOM, or just bypass it entirely with some gator clips and see if the error goes away.

[juliandev]

Hi,
we checked the oven flaps, and they open and close in the same way as other versions of the 5890 do in our lab.

I'm still confused about how to check the oven door mechanism.


I can measure both continuity as well as resistance between A & B even when the door is not shut.
Am I missing the obvious here?

consequently bypassing it with an alligator didn't do a difference

Thanks for the steady support
Julian

[aidnai]

Maybe I'm totally off base here. I am not aware that there is an oven door sensor per se. My 5890 doesn't care if the door is open or shut, except when it figures out it can't maintain the desired temperature.

Is your GC holding the set temperature? [edit] re-read your first post, seems like it is not. I believe the 5890 will give that error "oven shut off" when it gives up trying to control the oven temperature. The fact that none of the heated zones are working stumps me.

[aidnai]

The mainboard does some of the power switching for the detector/injector/aux zones. I don't remember it doing anything for the oven though. But there are a couple chips on the mainboard that if they go bad, there goes all of your zones. Does your mainboard have pretty much only DIP/through-hole components? Or a mix of through-hole and surface mount? If you have one of the old boards and are up for an adventure -- read this old post.

viewtopic.php?t=2091

Doing more research myself (I had this very thing happen, the injector zone fan broke and blew up the chip on the mainboard), I found that the agilent part number corresponds to a UDN2981A available from Allegro. See the datasheet here http://www.futurlec.com/Others/UDN2981A.shtml. Buy it at mouser or digikey, I think it's only a few bucks. You have to know how to solder (and desolder) though.

For posterity, my info came from here http://matthieu.benoit.free.fr/cross/co ... p-part.htm -- search for the HP part number and it cross references to the part number I listed above.

When mine blew up I was able to see the damaged chip by inspecting very closely. These are located at the top right of the mainboard near the auxiliary pin headers and connectors.

Big caveat -- I don't remember this disabling my oven so it may not be the same issue.

[AZBiodiesel]

Have you actually removed the oven shroud and visually inspected the wires/connections? If they are arcing out or not connected properly it may be causing the oven to not reach temp. I know you say you checked the resistance through the wire but how did you do that? I would disconnect the heating wires from the board and take the shroud out of the oven and visually inspect for charred areas. I have had oven shutoff on two 6890's and two 5890s it has always been the heating coil connections arcing out and breaking at the contact points or the wires themselves arcing further back in the insulation.

[juliandev]

@aidnai
that is valuable information.
I found the chip you referred to on the main board. It looks fine. Same for the other similar looking ones. However, you never know for sure until you see the board from both sides. Most of the components are through hole soldered.

It remains a big mystery to me, how oven fan oven heater and auxiliaries fail at the same time. According to my understanding of the circuit wiring diagrams, these are not related. As you said, oven fan shouldn't be (main board) controlled. It should start up, as soon as power is applied, since the fan operates on 120V and is not fed through the main transformer (correct me if I'm wrong).

In the old post you linked, people reported of fried chips on the mainboard, because of shortening/failing of other components, i.e. the fan. I suspect, that a short in a heated trap (aux port), coincided with the initial oven shut offs for our 5890. Maybe this led to damage on the main board. Still it wouldn't explain, why the fan is not running?!

Thanks again
Julian

[juliandev]

Have you actually removed the oven shroud and visually inspected the wires/connections? If they are arcing out or not connected properly it may be causing the oven to not reach temp. I know you say you checked the resistance through the wire but how did you do that? I would disconnect the heating wires from the board and take the shroud out of the oven and visually inspect for charred areas. I have had oven shutoff on two 6890's and two 5890s it has always been the heating coil connections arcing out and breaking at the contact points or the wires themselves arcing further back in the insulation.

Thanks for sharing this.
So far, I disconnected the heating coil from the AC power board and measured the resistance. In HPs service manual a reference value of ca. 9.6 Ohms is listed, and that is what I get. I haven't dissembled the oven shroud yet. We will look into that.
Then again, it's strange how a burned heating coil affects the other heated zones, unless this short backfired to the main board and damaged it.

[juliandev]

*** little update
We powered both oven fan as well as oven heater from a separate 120 V line and both components work just fine.

The only parts between the mains line in and the oven fan are one 5A Fuse, contactor K1 connected to a triac (all located on the AC Board). We swapped in an exchange AC board as well as an exchange triac, and still the oven fan won't operate. However, following back the circuit paths from contactor K1, it seems that this component is getting inputs from the Main Board through P26

P26.2 is Oven Control (to pulse transformer and oven triac gate)
P26.3 is K1 Oven Contactor Control.



So unlike the service manual states, oven fan is controlled, by K1, which is controlled by P26.3 (to mainboard). So, I conclude (considering that the fan and heaters functionality have been positively tested), that our problems are on the main board side of the instrument