avatar: MT
MT
5 posts
Replied to MT's post on October 22nd, 2012

Hi, I'm hoping the wise folks here can lead me in some direction to correct the following problem. I have an older Beckman DU-640 that has an increasing frequency of the Light Path Failed message appearing when I start it up. I have checked the sample chamber and have done a wavelength calibration to no avail.  Are there any diagnostics that I can run to eliminate or narrow down the problem? Thanks.

avatar: gr
gr
37 posts
Replied to MT's post on October 23rd, 2012

Most basic thing first;

Replaced vis lamp?

Aligned Vis lamp?

 

avatar: MT
MT
5 posts
Replied to gr's post on October 23rd, 2012

Thanks, gr. I aligned (peaked) the Vis lamp and it was off by about 46%T. Upon re-starting everything passed. Hopefully that has solved the issue. If Light Path Fail re-appears I'll update this post. Thanks again!

avatar: MT
MT
5 posts
Replied to MT's post on August 14th, 2013

Well, it has been working for nearly a year, but the Light Path Error is back on every start up. I have checked the Vis alignment (spot on) and have replaced the Vis lamp. Any suggestions on what to check further?

avatar: dpkleessr
dpkleessr
259 posts
Replied to MT's post on August 14th, 2013

Several issues can cause a light path failure at start up.  Just because the lamp is aligned does not mean that it has sufficient ENERGY to pass the start up sequence.  The detector for the DU640 requires 1V DC minimum at start up in order to continue on.  You cannot determine how much energy is actually being detected by using the %T value to peak the lamp.  This process only tells you that the lamp is peaked, not the actual energy value.  The only way to determine the actual energy is to use a DVM on the test point near the left front corner of the main board right in front of the connector that goes to the detector assembly.  If it is less than 1.0 Vdc then it could still be the lamp.  Are you using a Beckman lamp because not all visible lamps are created equal.  We tried for years to come up with an off the shelf replacement lamp but none are made to Beckman's specifications, especially in regards to the coating on the outside of the lamp.  The other big issue is when was the last time that your optics were cleaned?  Everything from the beam combiner,which can be rotated, all the way to the detector needs periodic cleaning and please, if you REALLY don't know what you're doing as to cleaning the optics, especially the grating assembly, then call someone in that actually does know how to clean them properly.  There's a lot of misinformation out there on how to clean the optics so be careful where and who you get the information from.  If you scratch the grating assembly as this item does not have a coating on it, then you are looking at a VERY expensive replacement part not to mention the fun, or lack thereof, of actually aligning the grating assembly.  Something else best left to a factory trained service engineer.  Hope this helps but I believe you really are in need of service on your DU.

Don

avatar: dpkleessr
dpkleessr
259 posts
Replied to dpkleessr's post on August 14th, 2013

One other item that I forgot to mention in my previous post, following the instructions in the operator's manual on visible lamp replacement is not really complete.  There is an up/down alignment as well as a left to right alignment.  The up/down alignment can only be done by actually taking the Visible lamp holder out of the DU if it needs adjustment.  Do you have a target assembly for the lamp alignment?  Every Beckman trained engineer has one and it is essential to a real lamp alignment for both lamps.  Anything else is guesswork at best.

Don

avatar: MT
MT
5 posts
Replied to dpkleessr's post on August 14th, 2013

Thanks, I will be moving this to a new building in a few months so may have a tech visit then. In the meantime; I replaced the Vis lamp with one from Sonntek (L835), but also found an original unused Beckman lamp, neither removed the error.  And as far as I know I do not have a target assembly.

I run this almost exclusively in the UV range (280-400nm); will this light path issue interfere within this range? I have run some know samples and the scans are nearly identical to previous ones from before the error message.

avatar: dpkleessr
dpkleessr
259 posts
Replied to MT's post on August 14th, 2013

As you may have discovered, even if you get a light path failure, the DU can still be used by just closing down the error display screen.  Actually, you are running your samples in both the UV and Vis range.  The switch over point is at 325nm at which point you are getting light from both lamps illuminating your samples until around 350nm where it switches over exclusively to the Visible lamp.  The fact that your scans are nearly identical probablly indicates that you're not being adversely impacted by the visible lamp issue.  Are you using a microcell holder for your samples?  If you are then you can get a better idea as to how well your lamp is actually aligned without having a real alignment tool.  With both lamps on, select 0nm as the wavelength in the fixed wavelength mode.  That will give you a very intense white light.  The light beam should be adjusteded such that the light is hitting in the center of the cell holder window left to right and should also be flooding the slit on the cell holder.  The beam may appear to be a little diffuse when you look at it but you need to remember that the focal point for the lamps is within the center of the cell.  Goingforward, do yourself a favor and only use Beckman visible lamps.  No one else makes a bulb that is completly compatible with your DU.  Beckman did extensive testing with Osram to get visible lamps that are meant for the DU.  They are relatively inexpensive but will give you the best performance.

Don

avatar: DonL
DonL
6 posts
Replied to dpkleessr's post on September 16th, 2013

We have a du650 and upon setting the RediRead to 0nm, the vis light beam falls short of hitting the exit slit. The only diagnostic test that fails is the light path. How do we get the grate to aim the vis beam at 0nm to hit the exit slit?

avatar: dpkleessr
dpkleessr
259 posts
Replied to DonL's post on September 16th, 2013

My first response is that YOU don't. The replacing or alignment of the grating is truly something that is best left to a service engineer that actually knows the correct procedure. Otherwise you just end up with more problems than you really want to deal with. The physicsl replacement of the grating is minor. The alignment is not and anyone that says it is is only lying to you. This was the most hated job on the DU600/800 Spectrophotometers for any BCI engineer. Sorry that I can't help you but this is more of a show and tell technique than a type and tell.

avatar: DonL
DonL
6 posts
Replied to dpkleessr's post on September 16th, 2013

Then PLEASE help connect us with a serviceman for the Cleveland, OH area. I have rebuilt this du-650 from the ground up and am faced with this last issue. The mirrors or gratings were never moved or replaced, just cleaned. Also, why do the 3 Wellnut screws run so long? Are they just used in shipping and should be totally loosened before operation? If I tighten them down any, they will dig into the tabletop below. I have new Wellnuts in place. Thank you for your help!!!

avatar: dpkleessr
dpkleessr
259 posts
Replied to MT's post on September 16th, 2013

Sorry Don, I don't work for Beckman Coulter anymore. You need to contact them directly with either the System ID # if the spec still has one attached or the model and serial number. The 3 screws that hold the optical bench in place should not be tightened down to the point where they bottom out on the lab bench. That would eliminate their anti-vibration function for the optical bench. You may have never moved the optics but if you have completely rebuild the spec then you may have accidentally changed the position of the wavelength drive system as that is what needs to be adjusted to get the white light back on the exit slit. I guess that I should have asked what the position of the white light is relative to the exit slit? Is it off to the side or is it above or below the slit? Get back to me and we'll go from there.

Don K

avatar: DonL
DonL
6 posts
Replied to dpkleessr's post on September 16th, 2013

You have no idea how grateful we are that you are responding to us, as I am sure others are enjoying your answers as well as they are spot on full of information in bringing Beckman du's back to life. As part of my rebuild I replaced all of the foam rubber which had turned to muck. I used the exact same thicknesses and cell structure (open and closed) for the various types of foam strips replaced. We properly cleaned the mirrors/grates using procedures as described by lens manufacturers. In relation to the exit slit, when setting the RediRead to 0nm for the calibrate procedure, the vis light circle is slightly off to the left of the slit (zero order error code). And yes, we did move the wavelength drive system through its range during re-construction. The drive seems to find its way home (almost) during warm-up diagnostics as all tests pass except light path. Is there a setting in the service mode to fine tune the stopping point for the vis light path to hit the exit slit dead on? Thank you again Don. We are a new company on a very limited budget, hence the Beckman Uv-vis instrument rebuild need. 

avatar: dpkleessr
dpkleessr
259 posts
Replied to DonL's post on September 17th, 2013

You're welcome and I'm glad to share some of my 32+ years of experience with those that appreciate it.

I bet you really enjoyed replacing those foam pieces. The heat build up from the lamps is what causes the turn to a sticky mush situation. The field engineers begged for years to get a kit of all of the foam pieces but it never happened.

Sorry to say that there is nothing built into the firmware to move the position of the light at 0nm. With you telling me that the light is slightly off to the left it appears that you've had a small amount of wavelength drive cable slippage. This can be from any corrosion on the "D" shaped pulley, look for any grayish powder on the pulley and/ or blue cables, or if you pushed the wavelength drive pulleys too hard while checking things out. It's the ability to get the cable slipped back into position that gets everything working properly again because even small movements of the pulleys and cables results in large movement of the beam. Again, as a show and tell it's not too bad applying the tricks we learned over the years but without seeing the condition of the pulleys and cables it's not something that I would ever try over the phone. The blue cables and pulley do have a finite lifetime so they may both need to be replaced especially if the spec was previously used in an acidic environment. This would be indicated by a black trail running over the aluminum chasis.

Now, as to the mirrors and grating cleaning. What you read may not be applicable to your spectrophotometer's mirrors and especially the grating. The grating, unlike the rest of the mirrors, does not have a coating so you must be EXTREMELY careful with cleaning it. Whatever cleaning solution you use, I used windex in a 90/10 dilution with 95% ethanol, you should use real cotton balls and not the synthetic ones available as they can scratch even the mirrors. The grating is only cleaned using straight top to bottom strokes. Anything else can really mess it up. Always rinse the mirrors and grating with your best deionized water and blow dry with canned air. Also make sure that your canned air does NOT have any anti-huffing agent in it because we found it permanently messes up your mirrors. Before you start cleaning any of the optics, pack paper towels around the bottom of the mirrors and grating bearing to catch any excess liquid. Also don't forget about the glass filters in the filted wheel assembly as they get fogged up too. They should be carefully removed from the filter wheel, cleaned like the mirrors and dried before replacing them in the filter wheel assembly. Otherwise, you get dirty cleaning fluids running out from underneath the little copper keeps that hold them in place.

Unfortunately, none of what I just shared with you will help you fix your main issue which I believe is definitely wavelength cable/ pulley related. Only experienced eyes-on can tell for sure what needs to be done. Unfortunately, Beckman's service rates are pretty excessive. They were $350/hr portal to portal when I retired almost a year ago so I can only imagine what they are now. They also went a lot of crazy with jacking up the cost of replacement parts so be prepared for some sticker shock if anything has to be replaced. Good luck and feel free to get back to me if you have any other questions.

Don

avatar: DonL
DonL
6 posts
Replied to dpkleessr's post on September 17th, 2013

Hello Don, Thank you for your informative reply. The D pulley as well as the cable look great. No traces of corrosion or powders on the pulley or cable. I see the D pulley cable runs over to a drive pulley with an abrasive finish on the shaft to avoid slippage. I think that run time with an ensuing slow build-up of slop has moved it slightly out of position. If you could just give me a just hint on how to slip the D pulley in relation to the drive pulley just a tiny tad, then I will hopefully be able to get the 0nm vis light spot focused on the exit slit rather than to the left of it. I do have a second parts unit to test a suggested procedure out on it first. I see the drive pully is connected to another pulley above it that has extended tabs on it for position sensing. Thank you again for all this great information. 

avatar: gr
gr
37 posts
Replied to DonL's post on September 17th, 2013

I had similar problems with my DU-650, and found that  two things were going on;

one of the filters in the filter wheel had become "frosted", and the tape /glue holding the exit slit had allowed it to sag out of position. Here are my note on fixing;
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Beckman DU-650 spectrophotometer notes rev 1-00.doc

Scanning Tips and Hints:

1)   Beckman DU-650, sn 4321024, software ver M, vis lamp is Osram 64425,12V,20W

2)   During scanning, baseline, or any reading, this machine is affected by vibration, pressing the case, touching the instrument, touching the table it sits on, and often nearby footsteps. Do not use mouse on top of machine.

3)   Scan blank just before measurement scan (prevents drift error)(vibration affects scanning blanks also!)

4)   For fixed  wavelength or RediRead use 0.5 sec average time.

5)   Scans at 1200nm/min = 1 nm res.  600nm/sec= 0.5nm res

6)   Lamp warmup time; vis 0.5 hr, UV; ???

To align lamps;

1)   Use RediRead to set at 200nm

2)   Align UV by loosening 4 screws and sliding the casting holding both lamps left-right for peak reading. If you have the optical cover off, center the violet circle on the entrance slit. Tighten 4 screws.

3)   Use RediRead  to set at 500nm

4)   Align white lamp-loosen 2 lamp screws and adjust lamp front-back for max reading. If you have the optical cover off, center the bright slash of light on the entrance slit.

Slit Alignment;

1)   With the optical cover off, use RediRead to set to 0nm. This will show a bright stripe of light on the exit slit, which should be centered on the slit. If not centered (or at least fully covering the slit), loosen the tape holding the slit and move it so that the slit is centered and parallel to the stripe of light.

2)   Change RediRead to 500nm. Verify that the slit is positioned vertically so the color band is fully getting through it.

Service Mode; the password for entering is the sum of the current time (example; 12:33 is a password of  9) .

The existing Cal info can be viewed in service mode in the DRP/ Cal Info menu.

Digital Optical serial mouse, model Q500;

Requires special mouse pad with H and V lines (should come with mouse). Available on Ebay and Amazon.
-------------------------------------------------------------------------------------------------

Problems:

One filter on the wheel (dark blue), had a frosted surface which would not come off with alcohol or lens cleaner. Oil was temporarily put on the filter to clear it for testing. On cleaning, the ground surface was no longer evident and this did not change with acetone, alcohol, or lens cleaner. The filter was scanned and found to be Hoya B390 (390nm center, 125nm bandwidth). It is nominally 2.5mm thick and is available from Edmund.

The calibrate wavelength function was not working. Because of this auto gain cal was not running so scans ran off scale. Running SETSCANGAIN fixed the gain problem. The wavelength was off by about 7nm.

All mirrors (except grating) were cleaned, lamps and slits aligned, a 2 hour warmup done and wavelength cal was then successful.

DRP/calib info reports the UV gain settings to be 255, and most of the visual range to be in the 36-72  range. It is likely that the UV lamp is quite weak.

The main circuit board has plug in daughter-boards which use a “bumper” to prevent the card from having cantilever problems. The rubber user for these had dissolved into a liquid which flowed several inches across the copper traces, sockets, and IC’s. As much as possible was removed using alcohol. New bumpers were installed.

avatar: dpkleessr
dpkleessr
259 posts
Replied to MT's post on September 26th, 2013

Sorry that I haven't gotten back to you but I've been off line for awhile. This is the kind of procedure that I might be able to talk you through but I don't think that I can really help via emailing. It's a little too cumbersome so if you want to talk real time then send me a good phone number so that I can call you when you're in front of either spec and we'll see what we can do to get you back on line. My personal email is walkingscrewdriver@yahoo.com.

avatar: LarryS
LarryS
1 posts
Replied to dpkleessr's post on January 23rd, 2014

Hi, I'm bringing up a new-to-us DU650. I got the optical path aligned (thanks for all the pointers in this thread!) When I check the UV gain settings on the service screen, they are all at 255. A previous post mentioned that this indicates a weak UV bulb. Is this indeed a sign that the bulb is near end-of-life and should be changed?

avatar: DonL
DonL
6 posts
Replied to dpkleessr's post on January 26th, 2014

Beckman DU: "Light Path Failed" fix as a follow-up to my September 17, 2013 post question> The alignment of the Beckman DU grate is actually relatively easy, with the right tool being used! Personally, I used a Vaco "C" washer spreader tool to relieve just enough tension off the string that is so tightly wound around the D pulley located immediately under, and connected to, the grate. Set the Vaco tool to spread (not squeeze) the tool's two individual head prongs apart while the two handles are being hand-squeezed. Stick the two relaxed prongs into the tension spring, one right at the begining and at the other at the end of the spring. Then just spread the tension spring open a very, very slight bit and gently rotate the D pulley a fraction at a time. Move the tool along in the rotation direction to keep even "hold open" tension on the spring.  Reset the machine and see if your new alignment is "spot on" or not. (The beam may move a bit until the new string positioning sets in). If not, repeat until the beam zero's in on the slit. It's really that easy; however, do not try to forcibly rotate the D pulley without relieving the string tension as the abrasive coating on the D pulley can mess up the string's gripping surface, just like sandpaper on clear plastic would! My alignment method is probably not by the Beckman book, but it works. Got two Beckmans up and running this way. Solution by Don Ladanyi

avatar: DonL
DonL
6 posts
Replied to DonL's post on January 26th, 2014

Solved my own question. When replacing the rubber Wellnuts, tighten them down ONLY for shipping. In use, loosen the long screws just enough to be even with the bottom of the Wellnuts.

avatar: dpkleessr
dpkleessr
259 posts
Replied to DonL's post on January 26th, 2014

Nice job and you exibited a good grasp of the issues with adjusting the drive pulley and cables.  I wish that I had known that such a tool existed while I was still working because it would have saved a lot of grief with this problem.  I salute your ingenuity but not your choice to gloat over your success.  Not exactly a professional response to resolving a service problem.

avatar: dpkleessr
dpkleessr
259 posts
Replied to DonL's post on January 27th, 2014

You should also know that there can be another issue with the rubber isolation mounts and associated hardware.  If you get a noisy baseline, Remove the three screws that hold the optical bench in place and using some fine emery cloth, polish the copper springs and the surfaces of the optical bench that come in contact with the copper springs to remove any oxidation.  This MAY resolve a noisy baseline problem but if it only reduces the noise, then I recommend attaching a ground wire from one of the two screws on the back of the detector assembly and attach it to a good ground.  When the DU800 series was released, which has the exact same optical bench, it came with this ground wire already installed.

One final point on the isolation mounts, do not allow them to be too loose as this can also contribute to electonic noise in the optics.

Don