avatar: Adam
2 posts
Replied to Adam's post on September 6th, 2012

HPLC 1090.  Everytime I turn on the pump on instrument, within 1 second the LoPr is switched and the pump sees an error.  What can I attribute this to and how can I fix this problem?

I also got here by googling where to find an HPLC 1090 user manual and I would still like to know if there is a place to download it.  My company will surely pay for one, we just can't find ours.

avatar: frarazzo
1 posts
Replied to Adam's post on September 10th, 2012

Verify if the inlet valve the left below the High pressure pump is not clogged.

Try to disconnect from the inlet and switch on again. If the problem is solved, investigate on the filter inside the housing, then exchange the valve.

Otherwise the trouble is the hipress. pmp

avatar: Panter
13 posts
Replied to frarazzo's post on October 17th, 2012

Hello guys,

Apparently, I have also encountered much of the same problem. 

The instrument in question here is HP1090 series II, ternary system with DAD  and FLD.  The only difference here would be that LoPr flag is raised just a fraction of a second after any of the injection pumps are activated. Booster pump works fine. What I've done so far was:

-checked inlet filters, checked and changed both valves on the booster pump, and I believe I've put them in, the right way. Still LoPr.

-Disconnected the inlet tube to the pump. Still LoPr.

-Checked the LPCompliance sensor connector, it is fed with correct +-12Vdc and a proper ground. Output without pressure applied lies between -10 to -20mVdc with a bit of noise, but, as I've read, that should be ok. 

-I do believe ihat injection pumps are good since there is a low chance of them failing exactly at the same moment. And those were proper, previously.

Now, here comes the question:

Is there a way to override this LPC check/flag so I could run injection pumps and check them?

So far, since I've not found anything mechanical, I believe there must be something wrong with a circuit that deals with this signal so it raises a no-go flag.

I do have Agilent's ,manuals but those do not contain any, even slight hint of, electronic schematic. So, I'll have to lose quite a lot of time in order to trace which circuit rises that flag.

Does anybody have anything in mind?

Thanks guys, in advance.

avatar: Panter
13 posts
Replied to Panter's post on October 22nd, 2012

After all it was the LPC sensor. 

The prestress excentre gave way a bit (but enough), probably due to pump vibrations and the fact that it did stay there for quite some number of years.

I've had to remove it, put it on a test bench and check it's readings against applied pressure, calibrate a bit and put it back.

Works like a charm.

The only thing for this calibration to work, the +-12Vdc PSU needs to be symmetrical.

I hope this will help someone.

avatar: Adam
2 posts
Replied to Adam's post on November 5th, 2012



Thanks very much for your descriptive answer to my problem.  It actually helped a lot.  I got very busy and didn't have time to mess with this problem, but I just looked back into it today and I found everything that you have spoke about and I understand it. 


I have removed the LPC and I am getting ready to bench test it as you spoke of.  Do you have any advice or details on how to accomplish this bench test?  Thanks very much in advance. 



avatar: Panter
13 posts
Replied to Adam's post on November 5th, 2012

Hi again,

Well, I've used a +-12Vdc PSU that I've made myself. You will not have to do that, it seems perfectly alright to do it within the instrument.

I've been lucky that two trimpots actually were quite properly set, so, I've had two less fiddlings to worry about.

Here's what you'll need.

-Three plugs, (call them stoppers or whatever), you can take them from some old columns, use them and return afterwards. disconnect all three injection pumps and plug the holes.

-You'll have to make an adapter and use the compressed air line (only if it does not come from a compressor, but from a cylinder, otherwise you'll get your LPC contaminated and you do not want that. THIS IS IMPORTANT!) Otherwise use some clean gas (NOT FLAMMABLE NOR OXIDIZING) Since your air cylinder already has a pressure regulator, see if it is capable to reach about 8bar. That is about, top pressure you should ever reach.

-A good DMM, and a set of clips, or tiny probes and someone to hold them. Also you'll need a phillips head straight, and a flat (say 4.8mm) bent screwdriver. The latter one needs to produce some masive torque. Also, you'll need a  small flat head trimmer. Dentist's mirror would be fine too. And, oh yes, take your wife's/girlfriend's nail lacquer, and try to get away with it.

-Somewhere in the service manual, in the SDS section (i think) there is a graph of the LPC response. (P/V)

-Pins on the flat connector are as follows: 1.-purple-(+12V), 2.-gray-(-12V), 3.-white-(0V), 4.-black-output. Of course, you'll measure all but you need voltage over the last two.

-When LPC is in a normal position, two trimpots should have their screws at the left, back side. There are two holes at the left side, although removing the cover seems like a good idea.

-From the graph you should see that the LPC is prestressed to start from -1V at 0bar. There was the problem with mine, If under no pressure it gave some few mV. Actually I've only moved the big screw at the left (I think) and it went ok. DO IT CAREFULLY, VERY SMALL MOVES PRODUCE QUITE A RESPONSE. And you do not want to overdo it. After just doing that, it gave me proper readings in accordance with the graph, which meant that I did not need to touch trimpots, which I cosider quite a luck.

-And , of course, I've polished my nails afterwards.

So, best of luck to you too.


And, yes, do flush and prime the system properly prior to letting it run. Bubbles can be annoying there and create quite some havoc.


It seems I've forgot. Could be, that bent screwdriver was even 6mm. You'll have to look it up yourself.